Toxic gas exposure toxicity levels & exposure limits for indoor environments:

this document outlines gas toxicity levels for a range of indoor gases which may be produced by heating systems, septic or sewer systems, building product outgassing, mold and MVOCs, heating systems, sewer lines, fire damage, or contamination from nearby industrial, beauty parlor, dry cleaning, or other activities which often produce noxious or toxic odors and gases.

Indoor Gas Exposure Limits, Gas Testing Limitations & Definitions

Definition of "Gas Exposure" - General Information about Exposure, Standards, Definitions

"Exposure" as used here is the contact that a person (or animal) has to a substance whether or not protection is provided by respirators or other protective equipment. Exposure to a liquid or gas can occur through various means such as breathing (inhalation), eating or drinking (ingestion), skin contact, or skin absorption of the chemical into the body.

Human exposure to certain potentially harmful chemicals found in liquids, gases, or solids is regulated in most countries but regulations (as well as test procedures) may vary significantly depending on whether the exposure is being regulated for industrial exposure of workers (in the workplace where higher levels of exposure may be anticipated) or exposures of consumers or individuals (out of the workplace, such as by consumer goods).

Watch out: exposure levels and test methods to determine the level of exposure of individuals in the workplace may not translate readily to potential exposure levels in other environments such as the home.

It is our OPINION that these two environments (home and workplace) are very different. For example, exposure to certain chemicals or particulates may be much higher in the workplace than in the home.

And exposure to potential contaminants in the home may be complicated by the presence of multiple chemicals or particles, varying indoor conditions (air movement, temperature, etc) that mean that using an industrial standard or measurement method in the home would be quite inappropriate.

Gas Exposure Standards (workplace-based)

The purpose of general indoor gas exposure inspection and testing is to perform a general screen for the presence of specific problematic substances in response to specific concerns raised regarding the target property

. Individual complaints about indoor air quality or smells can occur at extremely-low levels of certain gases or particles, in fact at levels considerably below typical allowable industrial permitted exposure levels (PEL's). Therefore we may select tests which screen for levels of gases considerably below permitted limits for industrial workplace exposure.

Important Gas Testing Safety Warning:

because even small changes at a building can make an enormous difference in the presence or absence of a dangerous gas, consumers and investigators must keep in mind that any gas detection test represents conditions only at the instant that the test was performed.

Simply turning on a fan, closing a door, or turning on or off a piece of heating equipment can change from safe to very dangerous conditions in a building. For this reason, gas testing alone, without a careful building visual inspection and history-taking, is unreliable as a safety indicator, particularly when the test does not detect the presence of a gas being sought.

Important Gas Toxicity & Exposure Limit Note:

 in most cases the toxic gas exposure limits available are for workplace settings. Conditions in the home, including assumptions about the health, age, and level of physical activity of occupants in a non-industrial setting are likely to mean that industrial exposure standards, while useful, are not a completely satisfactory safety guideline for other settings.

Definitions of Workplace & Other Exposure Limits

Question: what does "TLV" stand-for?

2020/02/29 Peter Ravenscroft said:
G'day,

Ta for the info. Much appreciated, as I am reonably sure from the satellite maps, that the Wuhan Chongqing etc problem is SO2 air-poisoning from their Al and steel plants burning hi-S petcoker anodes, virus a normal coronavirus and trivial

On dangers of SO2, you failed to explain what "TLV" stands for.

This Q&A were posted originally

at SULPHUR DIOXIDE GAS TOXICITY

Reply: Definition of TLV, STEL and PEL: Workplace Exposure Limits

Thanks for the comment, and for the helpful question Peter

Definition of TLV

"TLV" stands for "Threshold Limit Value" - a long term limit on daily exposure for workers, defined as the maximum daily exposure of a substance to which a worker can be exposed over a working lifetime without adverse health effects.

In the U.S. and some other countries organizations like OSHA ( Occupational Safety and Health Administration) set a TLV for workers.

From OSHA: The OSHA definition of work environment is primarily composed of: (1) The employer's premises, and (2) other locations where employees are engaged in work-related activities or are present as a condition of their employment. The employer's premises encompass the total establishment. - there are some exceptions and additional details available from OSHA: retrieved 2020/02/29 original source: www.osha.gov/laws-regs/standardinterpretations/1992-03-31-1

Definition of STEL

Short Term Exposure Limit - the acceptable average exposure over a short period of time, usually 15 minutes as long as the time-weighted average is not exceeded.

Both STEL and TLV are workplace exposure limits.

Definition of PEL

Permissible Exposure Limit: the maximum amount or concentration of a chemical that a worker may be exposed to under OSHA regulations.

Also see GAS EXPOSURE EFFECTS, TOXIC

Types of Gas Exposure Tests, Instruments

Gas Tests:

Gas exposure or gas leak test equipment is checked for proper operation and calibration before and after the investigation; gas detection tests are conducted under operating conditions meeting the manufacturer's requirements; these tests are applicable only to the place, time, and date of measurement; the tests are not technically exhaustive.

Several gas detection instruments & methods are used, depending on whether we are screening for presence/absence of combustible gases, checking general indoor air quality, or testing and making quantitative measurements of specific gases in an environment. Some instruments are particularly helpful in tracking odors or leaks to their source.

Draeger Sampling Pump:

We use the Draeger accuro™ Pump and Draeger-Tubes for gaseous substance sampling for both detecting the presence/absence of specific gases and for quantitative measurements of gas levels.

The Sensidyne™ Gastec piston pump and Gastec™ tubes for test for presence/absence of and level of certain gaseous substances.

Both of these toxic gas testing pumps are factory calibrated at 100 cc, and are leak-tested before and after each investigation. The adsorption tubes used for substance screening/identification are factory-calibrated. Other tests for specific substances: over 200 tests for over 500 different gases are available by using specific detector tubes.

I can provide these when there is risk of a specific substance in a building. Unless there is a reason given for a narrow specific gas test in a building such tests are not economical and are simply "shooting in the dark."

The TIF 8850 combustible gas detector

is a broad-spectrum gas screening instrument which is also useful to track and pinpoint the source of odors or leaks.

A partial list of gases detected by the TIF 8850 and its detection limits includes: [Note: these are instrument detection limits, NOT gas exposure limits which we in fact do provide just below

at GAS EXPOSURE LIMITS.

• Acetone gas exposure limit - 50ppm,
• Acetylene gas exposure limit - 50ppm,
• Alcohols gas exposure limit -
• Ammonia gas exposure limit - (R717) 20ppm,
• Benzene gas exposure limit - ,
• Iso-Butane (R600a) gas exposure limit - 500ppm,
• Chlorine gas exposure limit - 1ppm,
• Ethane (R170) gas exposure limit - 500ppm,
• Ethylene gas exposure limit - 500ppm,
• Formaldehyde gas exposure limit -
• Gasoline gas exposure limit - 1ppm,
• Hydrogen gas exposure limit - 500ppm,
• Hydrogen Sulfide gas exposure limit - 5ppm,
• Lacquer Thinners gas exposure limit - ,
• Methane (Natural Gas) gas exposure limit - 500ppm -
  
• Methyl Chloride gas exposure limit - 5ppm,
• Methanol gas exposure limit - 50ppm
• Methyl Ether gas exposure limit - 500ppm,
• N-Butane gas exposure limit - ,
• Naphtha gas exposure limit - ,
• Propane ("bottled gas" R290) gas exposure limit - 500ppm,
• Toluene gas exposure limit - ,
• Vinyl chloride gas exposure limit - 5ppm. MDL are generally 1-500 ppm.

The TIF 8800 device is essentially the same as the TIF8850 and uses a TIF 8801 sensing tip.

We provide detailed suggestions for using theTIF8800 combustible gas detector

at USING the TIF 8800 Gas Detector

We discuss alternative gas measurement tools

at GAS MEASUREMENT TOOLS

General exposure limits reference list for specific gases tested indoors

Some general notes for specific gases, their toxicity, exposure hazards, and exposure limits follow in an alphabetized list.

Also see GAS EXPOSURE HAZARD LEVELS: for Toxic Gas Exposure to Ammonia, Arsine, Arsenic, Bromine, Carbon Dioxide, Carbon Monoxide, Hydride, Ozone - allowable exposure levels and hazard levels. And see the NIOSH Pocket Guide to Chemical Hazards (this document is available online). Other comments in this section are from "Health Hazards of some Gases" Jack E. Peterson, P.E., CIH, Ph.D., May, 1987.

Ammonia Gas Characteristics, Toxicity, Simple Ammonia Gas Exposure Measurements

Ammonia "The current gas exposure limit TLV for ammonia is 25 ppm with a short-term exposure limit of 35 ppm. Both were designed to be low enough to cause no irritation in unhardened people. The OSHA PEL for ammonia is 50 ppm, as is the NIOSH Recommended Standard."[14], [15]

Ammonia exposure limits: NIOSH REL: gas exposure limit TWA 25 ppm (18 mg/m3) ST 35 ppm (27 mg/m3); OSHA PEL: TWA 50 ppm (35 mg/m3)

We provide more details about ammonia gas exposure hazards

at AMMONIA GAS EXPOSURE

Arsine Gas Characteristics, Toxicity, Gas Exposure Limits

Arsine : gas exposure limit "The effects of arsine are completely avoided if 8-hr exposures are kept at or below 200 ug/cu. m, (0.05 ppm), the TLV and PEL." (Op. cit.).[16]

Arsine gas exposure limits: NIOSH REL: Ca C 0.002 mg/m3 [15-minute];OSHA PEL: TWA 0.05 ppm (0.2 mg/m3)

We provide more details about arsine gas exposure hazards

at ARSINE GAS EXPOSURE

Benzene Gas Characteristics, Toxicity, Gas Exposure Limits

Benzene: 0.5/a: gas exposure limit for this test we select a sampling tube which is not Benzene specific (Draeger Benzene 0.5/a) in order to also screen for other aromatic hydrocarbons including toluene, xylene (more likely to be in carpet out gassing than benzene) and ethel benzene.

Benzene gas exposure limits: NIOSH REL: Ca TWA 0.1 ppm ST 1 ppm; OSHA PEL: [1910.1028] TWA 1 ppm ST 5 ppm. [17]

Bromine Gas Characteristics, Toxicity, Gas Exposure Limits

Bromine: "Bromine causes eye irritation and lacrimation (tearing) in concentrations below 1 ppm but above the TLV (and PEL) of 0.1 ppm. Concentrations irritating to the eyes should not be tolerated for more than 15 minutes." (Op. cit.) [18].

Bromine gas exposure limits: NIOSH REL: TWA 0.1 ppm (0.7 mg/m3) ST 0.3 ppm (2 mg/m3); OSHA PEL™: TWA 0.1 ppm (0.7 mg/m3)

We provide more details about exposure to bromine gas at

BROMINE GAS EXPOSURE

Carbon Monoxide Gas Characteristics, Toxicity, Gas Exposure Limits

Carbon monoxide gas: in general, no carbon monoxide (CO) should be found indoors in living or working spaces when performing an instantaneous check.

But CO monitors may be expected to sound an alarm when a time-weighted exposure level reaches 500 ppm, as that threshold is intended to protect lives while avoiding sounding false alarms that may occur, for example, when there is a brief, low-level CO release when a gas-fired appliance is first ignited.

NIOSH recommends a conservative PEL of 35 ppm, referring to an exposure of 8 hours/day, 40 hours/week, for a working lifetime " a workplace exposure limit. [19].

Carbon monoxide exposure limits: NIOSH REL: TWA 35 ppm (40 mg/m3) C 200 ppm (229 mg/m3); OSHA PEL™: TWA 50 ppm (55 mg/m3). Readers should also review our more detailed review of CO hazards

We provide extensive information about CO exposure at 

• CARBON MONOXIDE - CO
  • CARBON MONOXIDE HEATING SYSTEM CHECK
  • CARBON MONOXIDE INSPECTION
  • CO ALARM CAUSES
  • CO DETECTION OPTIONS
  • CO EXPOSURE LIMITS
  • HEAT EXCHANGER LEAK ALLOWED
  • HEAT EXCHANGER LEAK TEST STANDARDS
  • HEAT EXCHANGER CORROSION
  • HEAT EXCHANGER LEAK TEST
  • CARBON MONOXIDE INSPECTION
  • CO DETECTION OPTIONS
  • MEDICAL EFFECTS of CO
  • POISONING SYMPTOMS - CO

Carbon Dioxide Gas Characteristics, Toxicity, Gas Exposure Limits

Carbon Dioxide gas exposure limit "The highest TLV (and PEL) assigned to any material is assigned to carbon dioxide, namely 5000 ppm (NIOSH has recommended a Standard of 1.0% or 10 000 ppm for a 10-hr work shift with a ceiling of 3.0% or 30 000 ppm for any 10-min period).  Furthermore, these concentrations are far more an expression of good practice than a line between "safe" and "dangerous." [20]

Actually, the concentration of carbon dioxide must be over about 2% (20 000 ppm) before most people are aware of its presence unless the odor of an associated material (auto exhaust or fermenting yeast, for instance) is present at lower concentrations.

Above 2%, carbon dioxide may cause a feeling of heaviness in the chest and/or more frequent and deeper respirations.  If exposure continues at that level for several hours, minimal "acidosis" (an acid condition of the blood) may occur but more frequently is absent." (Op. cit.)

Details about carbon dioxide gas toxicity or CO2 exposure hazards are provided in a separate article

at Toxicity of Carbon Dioxide Gas Exposure, CO2 Poisoning Symptoms, Carbon Dioxide Exposure Limits, and Links to Toxic Gas Testing Procedures

More information about gas hazards, gas toxicity, or other environmental hazards is available from public and professional agencies and associations such as the American Industrial Hygiene Association (AIHA) www.aiha.org, OSHA www.osha.gov, and the Mine Safety & Health Administration www.msha.gov. Also see Industrial Hygiene News.

Carbon dioxide gas exposure limits: NIOSH REL: TWA 5000 ppm (9000 mg/m3) ST 30,000 ppm (54,000 mg/m3) OSHA PEL: TWA 5000 ppm (9000 mg/m3)

We provide extensive information about Carbon Dioxide gas exposure

at CARBON DIOXIDE - CO₂

and still more details about exposure to carbon dioxide gas exposure limits

at CARBON DIOXIDE GAS

Formaldehyde Gas Exposure Limits

Formaldehyde is an organic chemical with formula HCHO, CAS No. 50-00-0 that is very widely used in industry as well as in a plethora of consumer products from cosmetics and clothing to furnishings and construction materials as well as in disinfectants and preservatives.

Formaldehyde is an intermediate chemical used in the production of resins (e.g. glues in fiberboard and OSB, and in wrinkle-resistant clothing), industrial chemicals, preservatives (including in some cosmetics and skin creams), and in shampoos and glues.

Formaldehyde: (Formalin) gas exposure limits - As an additional example using Formaldehyde, in a screen I may test for very low levels in a building (.05 ppm), but the range of human response (also widely variable individually) may be summed as follows:

> 3.0 ppm = respiratory impairment and damage

> 1.0 ppm = possible nasopharyngeal cancer

> 0.5 ppm = irritation to eyes & mucous membranes

> .01 ppm = mild irritation or allergic sensitization in some people. [21].

Formaldehyde MSDS sheets: This FORMALDEHYDE MSDS [PDF] from Mallinckrodt Chemicals notes that typical composition of formaldehyde in industrial use is comprised of 37% formaldehyde, 10-15% methyl alcohol, and the remainder water.

Synonyms for formaldehyde exposure are Formaldehyde 37%, Formalin, Morbicid Acid, Methylene Oxide, Methyl aldehyde, all bearing the CAS No.: 50-00-0 and expressed by the chemical formula HCHO and CH3OH in water.

Formaldehyde exposure limits: U.S. Federal and State Level

• NIOSH REL: Ca TWA 0.016 ppm C 0.1 ppm [15-minute];
• OSHA PEL: TWA 0.75 ppm ST 2 ppm.
• OSHA Standard Number 1910.1048: FORMALDEHYDE EXPOSURE LIMITS [PDF]
• U.S. State Labor Department example of Formaldehyde Regulations:
  
  FORMALDEHYDE BASIC RULES [PDF], Washington State Department of Labor and Industries, retrieved 12/13/2010, original source: http://www.lni.wa.gov/wisha/rules/formaldehyde/html/296-856-200.htm

Details about formaldehyde gas exposure limits are found

at FORMALDEHYDE GAS EXPOSURE LIMITS - DETAILS

Details about formaldehyde hazards in buildings are found

at FORMALDEHYDE HAZARDS 

Also see FORMALDEHYDE GAS TEST KITS, METERS

Formic Acid Gas Characteristics, Toxicity, Gas Exposure Limits

Formic acid: this gas screen addresses acid gases which can be expected to be produced by fire, heat, or oxidation (such as from ozone treatment) in commercial and residential properties. Formic acid is readily metabolized and eliminated by the body. Nonetheless, some chronic effects have been documented. Excessive inhalation is a respiratory tract irritant.

Repeated exposure to formic acid gases (at higher levels) can result in an allergic reaction. It is a suspected mutagen, may cause long-term liver and kidney damage.  More about formic acid and its exposure effects can be read at http://encyclopedia.lockergnome.com/s/b/Formic_acid and at Cornell University's MSDS files: http://msds.ehs.cornell.edu/msds/siri/files/ckb/ckbjy.html - [22].

Formic acid exposure limits: NIOSH REL: TWA 5 ppm (9 mg/m3); OSHA PEL: TWA 5 ppm (9 mg/m3)

Formic acid gas exposure limits: NIOSH REL: TWA 5 ppm (9 mg/m3); OSHA PEL: TWA 5 ppm (9 mg/m3)

Hydrogen Sulfide Gas (H₂S) Exposure Exposure Limits

Hydrogen sulfide (H₂S) may be found or produced in buildings from a variety of sources and may be noticed as a sulfur, or rotten egg smell or even as a flatulence odor. Details about hydrogen sulfide sources in buildings are

at HYDROGEN SULFIDE GAS. Sewer gases also probably contain hydrogen sulfide gas (H₂S). Also

see SEWER GAS ODORS.

Hydrogen Sulfide (H₂S) Exposure Limits

In the U.S. OSHA's exposure limit for hydrogen sulfide gas (synonyms include sulfretted hydrogen, hydrosulfuric acid and hepatic gas) are expressed as PELs (permissible exposure limits) and are set as follows:

• OSHA Permissible Exposure Limit (PEL) for Hydrogen Sulfide (H₂S) Gas: 
  • General Industry: 29 CFR 1910.1000 Z-2 Table -- Exposures shall not exceed 20 ppm (ceiling) with the following exception: if no other measurable exposure occurs during the 8-hour work shift, exposures may exceed 20 ppm, but not more than 50 ppm (peak), for a single time period up to 10 minutes.
  • Construction Industry: 29 CFR 1926.55 Appendix A -- 10 ppm, 15 mg/m3 TWA
  • Maritime: 29 CFR 1915.1000 Table Z-Shipyards -- 10 ppm, 15 mg/m3 TWA
• American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) for Hydrogen Sulfide (H₂S) Gas: 1 ppm, 1.4 mg/m3 TWA; 5 ppm, 7.0 mg/m3 STEL
  
  National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL) for Hydrogen Sulfide (H₂S) Gas: 10 ppm, 15 mg/m3 Ceiling (10 Minutes)
• NIOSH Immediately Dangerous To Life or Health Concentration (IDLH for Hydrogen Sulfide (H₂S) Gas): 100 ppm

Details about hydrogen sulfide sources in buildings are in these articles

• HYDROGEN SULFIDE GAS
• SEWER GAS ODORS
• SULPHUR & SEWER GAS SMELL SOURCES

References for Hydrogen Sulfide gas exposure

• "HydrogenSulfide", United States Department of Labor, OSHA, reference, retrieved 2/2/2014, original source https://www.osha.gov/dts/chemicalsampling/data/CH_246800.html

Methane Gas Exposure Limits

Methane Gas Hazards are primarily of explosion or asphyxiation

We commented at SEPTIC SYSTEM SAFETY that methane gas which maybe encountered in septic system is both explosive and an asphyxiant. A

And we give those details

at METHANE & SEWER GAS HAZARDS

and METHANE GAS SOURCES

thoughtful reader, George Fielder, previously a salesperson for GfG Instrumentation, pointed out that these are the hazards. (We had inaccurately stated that methane gas was "toxic".)

In its pure form, methane gas is odorless and colorless. However where it occurs in or at buildings, methane may be mixed with other products that do provide an odor, such as in septic or sewer gases. The point is that one should not assume that there is no explosion or methane gas risk simply because no gas odor is noticed in a building.

Methane Gas Exposure Limits

The ACGIH TLV (Threshold Limit Value) described for Methane Gas is: Simple Asphyxiant. It is not classifiable as to its carcinogenicity.

Reference: OSHA describes methane, and its synonyms methyl hydride, marsh gas, and fire damp, at http://www.osha.gov/dts/chemical sampling/data/CH_250700.html where OSHA assigns IMIS Code Number 1640 to Methane gas.

Measurement Instruments for Levels of Methane Gas

Mr. Fielder added that additionally, toxic and combustible gases like methane and H2S that would be found in a septic tank can be readily measured by a portable, handheld gas monitor that can be rented from almost any safety equipment supply company or trench equipment rental company like United Rentals

. They are easy to use and understand direct reading instruments that if nothing else might satisfy the curiosity of the do-it-yourselfer who likes to stick his nose in it.

True the user will need to know and understand the measurement scale and exposure levels for the particular gases being measured but this also can be easily explained when renting said instrument and reviewing an MSDS sheet.

Most portable handheld monitors on the market today are less complex than a volt-ohm meter and can readily be understood with a brief explanation.

Consult Your Local Safety Equipment Distributor about Measuring Methane Gas or Entering Confined Spaces where Methane Gas is a Risk

Readers who have the need to measure methane gas levels or who have questions about the hazards of entering confined spaces such as septic tanks should contact their local safety equipment distributor for further advice. In addition, local fire & emergency service officials as well as gas distribution companies as well as some home inspectors or environmental testing firms may have expertise and gas testing or measurement equipment on hand.

More information about methane and other gas hazards, toxicity, or other environmental hazards is available from public and professional agencies and associations such as the American Industrial Hygiene Association (AIHA) www.aiha.org, OSHA www.osha.gov, and the Mine Safety & Health Administration www.msha.gov. Also see Industrial Hygiene News.

Watch out: Stay out of Septic Tanks

We emphasize that in ordinary procedures used in the care, repair, or maintenance of septic systems, the safety warnings we've listed above should be followed with care, and in general, quantitative measurements of the level of methane or other gases are not needed during a septic system repair.

More about Methane Gas Hazards

Readers who own, service, or live on a property which includes a private septic system should review

• OUTHOUSE / LATRINE FIRE & EXPLOSION
• METHANE & SEWER GAS HAZARDS
• METHANE GAS SOURCES
• SEPTIC & CESSPOOL SAFETY

Natural Gas Exposure Hazards & Limits

Question: gas leak burning in new Thermador natural gas stove

2020/02/22 Susan said:

Hello, I recently had exposure to strong natural gas while "burning off manufacturer chemicals" from a thermador 48" gas range.

Evidently it was a floor model that had been moved a lot and the gas pipe in the bottom of the small oven had been inadvertently disconnected from the main gas line coming into the oven which was causing a leaking blow torch in the bottom of my oven when turned on when I was told to burn off manufacture chemicals and that the smell was normal during the process.

It ran for 3 hours and the smell was very strong even though I had my vent hood on full force. I stayed in the room while doing this exercise because I was concerned something was wrong with the newly installed oven.

When I insisted there was something wrong the company sent a technician who found this pipe disconnected. He said we were lucky it did not explode. I am now experience heart arrythmias and am wondering if the gas exposure may have contributed to them.

Reply: potential hazards from natural gas exposure vs natural gas combustion products

Susan

Thank you for posting an important note. It underscores the dangers of relying on a perhaps-less-than-fully-trained manufacturer's rep on the phone - someone who didn't consider that a dangerous gas leak could be present.

The article above on this page discusses gas exposure limits for various gases.

Natural gas exposure hazards

are discussed by several researchers such as

• Brown, David, Beth Weinberger, Celia Lewis, and Heather Bonaparte. "Understanding exposure from natural gas drilling puts current air standards to the test." Reviews on Environmental Health 29, no. 4 (2014): 277-292.
  
  Abstract excerpt:
  Case study descriptions of acute onset of respiratory, neurologic, dermal, vascular, abdominal, and gastrointestinal sequelae near natural gas facilities contrast with a subset of emissions research, which suggests that there is limited risk posed by unconventional natural gas development (UNGD).
  
  An inspection of the pathophysiological effects of acute toxic actions reveals that current environmental monitoring protocols are incompatible with the goal of protecting the health of those living and working near UNGD activities.
  
  The intensity, frequency, and duration of exposures to toxic materials in air and water determine the health risks to individuals within a population.
• Boogaard, Peter J., Augus-Tinus AJ Houtsma, H. Louis Journée, and Nico J. Sittert. "Effects of exposure to elemental mercury on the nervous system and the kidneys of workers producing natural gas." Archives of Environmental Health: An International Journal 51, no. 2 (1996): 108-115.
  
  Abstract: Early signs of alterations in renal and neurological functions were studied in three groups of workers who were exposed to different levels of mercury that were below the current biological exposure index of 35 μg/g creatinine. There were no differences among the three study groups with respect to either motor nerve conduction velocity or tremor frequency spectra of physiological tremors.
  
  Also, no significant correlations were found between the results of the neurological tests and any of the present or historical biological monitoring data. In contrast, N-acetyl-β-D-glucosaminidase was increased significantly in the group with the higher exposure, compared with either the lower-exposure or control groups.
  
  N-acetyl-β-D-glucosaminidase was correlated strongly with mercury concentration in urine and was correlated weakly with historical biological monitoring data; however, there was no correlation with duration of exposure.
  
  These results suggest that after exposure to mercury at levels below the biological exposure index, a transient increase in N-acetyl-β-D-glucosaminidase can be observed, but is not an early indicator of developing renal dysfunction.
• Saadat, Mostafa, and Aminolla Bahaoddini. "Hematological changes due to chronic exposure to natural gas leakage in polluted areas of Masjid-i-Sulaiman (Khozestan province, Iran)." Ecotoxicology and Environmental Safety 58, no. 2 (2004): 273-276.
  Abstract:
  
  An overwhelming number of studies have given consistent findings that environmental or occupational exposure to oil products results in a significant decrease in circulating erythrocytes, hemoglobin, platelets, total white blood cells, and absolute numbers of lymphocytes and neutrophils. Some parts of Masjid-i-Sulaiman (located in the southwest of Iran) are contaminated by subsurface leakage of natural gas, which contains a high level of hydrogen sulfide.
  
  The amount of all reactive sulfur compounds in air of contaminated areas of MIS was estimated as equal to 0.023±0.002 ppm of SO2. In the present report the hematological findings of 99 persons from polluted areas of MIS were compared with those of 396 individuals from the general population of MIS matched by age (±3 years) and sex.
  
  The CBC test and the WBC differential were analyzed in one central laboratory according to standard hematological methods, by Coulter S (Biomedical). The multiple linear regression method was applied in order to detect differences among exposed and unexposed groups for hematological markers.
  
  The absolute mean number of red blood cells, percentages of hematocrit, level of hemoglobin, and absolute number of platelets were significantly higher among the exposed subjects compared with the control group. However, the absolute mean numbers of white blood cells, lymphocytes, and neutrophils were significantly decreased in the exposed group compared with the control.

Really? Keep in mind that studies of worker exposure will be assessing people probably at much greater risk than you - you had a one-time 3 hour limited exposure to an unknown level of natural gas (probably zero) and exposure to the combustion products of natural gas (carbon dioxide and water vapor) and exposure to unknown off-gassing of oils, coatings, etc. on the new Thermador gas range.

But of course we have not a shred of an idea of the actual exposure level nor exact duration of your exposure to the combustion products of propane nor whether or not the gas leak was burning completely or offgassing a mix of water vapor and CO2 and unburned components. ( In complete combustion the products of methane gas combustion from LPG or natural gas would be carbon dioxide and water vapor. )

Ask your doctor to comment on the probability that your current medical complaints are related to that event.

Thank you for the question - do keep me posted on what your doctor says and we'll add that information here in the article above under "Natural Gas Exposure" as that will assist other readers.

Also see

• METHANE GAS HAZARDS principal risks are explosion (or fire) or asphyxiation.
• NATURAL GAS & PROPANE COMBUSTION PRODUCTS
• PROPANE GAS EXPOSURE HAZARDS

Nitric Oxide Gas Characteristics, Toxicity, Gas Exposure Limits

"Nitric oxide is colorless and may have little or no odor. Nitrogen dioxide (and/or its dimer, nitrogen tetraoxide) is rust red and has a "typical" odor quite noticeable at 5 ppm and causes eye and nose irritation at 10 to 20 ppm.

From (1987), the TLV for nitric oxide is 3.0 ppm with an STEL of 5.0 ppm; the PEL is 5.0 ppm.

NIOSH has recommended 1.0 ppm for a Standard." (Op. cit.) [23].

See NITROGEN OXIDES GAS for more detailed exposure limit data.

Ozone Gas Characteristics, Toxicity, Gas Exposure Limits

Ozone Gas: "Ozone is a highly toxic gas but even highly toxic substances can be encountered safely. The main concern with this material is that concentrations to which people are exposed do not average more than 0.1 ppm over an 8-hr day, and do not exceed that value by more than a factor of 2 or 3 during the exposure." (Op. cit.) [24].

Ozone gas exposure limits: 

NIOSH REL for Ozone: C 0.1 ppm (0.2 mg/m3)

OSHA PEL™ for Ozone: TWA 0.1 ppm (0.2 mg/m3)

Details about Ozone Gas hazards and the use of ozone generators or using ozone as a mold remedy are provided in depth in an article series whose home page is given just below.

• Our complete list of articles about ozone can be found
  
  at OZONE HAZARDS - home
• Also see
  • OZONE EXPOSURE STANDARDS
  • OZONE TESTS
  • OZONE TOXICITY
  • OZONE MOLD / ODOR TREATMENT WARNINGS

Perchloroethylene (tetrachloroethylene) Gas Characteristics, Toxicity, Gas Exposure Limits

Hazards from perchlorethylene exposure widely discussed in research literature include lymphoma, lung cancer, bladder cancer, and other illnesses.

Perchloroethylene (tetrachloroethylene): - drycleaning solvent: [OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.] OSHA's former permissible exposure limits for perchloroethylene (tetrachloroethylene) were 100 ppm as an 8-hour TWA, 200 ppm as a STEL not to be exceeded for more than five minutes in any three-hour period, and 300 ppm as a ceiling.

On the basis of the chemical's narcotic effects in humans, the Agency proposed a revised PEL of 50 ppm TWA and a 15-minute STEL of 200 ppm for perchloroethylene; these are the limits recommended by the ACGIH (ACGIH 1986/Ex. 1-3, p. 464). NIOSH (Ex. 8-47, Table N6B) did not concur with the proposed limits and recommended that exposures be maintained at the lowest feasible limit and that this chemical be classified as a potential occupational carcinogen.

OSHA has evaluated the health evidence for this substance and has determined that a further reduction in the PEL to 25 ppm as a TWA is warranted, and the Agency is establishing this limit in the final rule. Perchloroethylene is a clear, colorless, nonflammable liquid with an etheral odor.

Perchloroethylene is widely used as a solvent in the dry cleaning industry and in industrial degreasing operations. The narcotic effects associated with exposure to high levels of this chemical are well documented. A worker exposed to an estimated concentration of 1470 ppm perchloroethylene and Stoddard solvent for 3.5 hours lost consciousness (Stewart, Erley, Schaffer, and Gay 1961/Ex. 1-807).

The most comprehensive studies of the effects of prolonged exposure to perchloroethylene vapors on human volunteers were conducted by Stewart and colleagues (Stewart, Hake, LeBrun et al. 1974/Ex. 1-970; Stewart, Hake, Wu et al. 1977/Ex. 1-971); these investigators concluded that prolonged exposure to 200 ppm results in early signs of CNS depression, while no response was elicited in men or women exposed repeatedly to 100 ppm for seven hours/day, except that performance on the Flanagan coordination test was significantly decreased in some exposed subjects (Stewart, Hake, Wu et al. 1977/Ex. 1-971, p. 28).
-- Excerpt from PERCHLOROETHYLENE (TETRACHLOROETHYLENE) - OSHA -- DJ Friedman. http://www.cdc.gov/niosh/pel88/127-18.html

Also see TETRACHLOROETHYLENE TRICHLOROETHYLENE - OSHA. http://www.osha.gov/dts/sltc/methods/mdt/mdt1001/1001.html+

U.S. EPA on Perchloroethylene

OPINION: unfortunately by 2020/02/22 the US EPA had spread out ints information on Perchloroethylene such that it becomes difficult to actually find definitive statements, exposure limits, or hazard statements. Here are some findings:

Perchloroethylene (also known as ethene, 1,1,2,2-tetrachloro, tetrachloroethylene and PCE) is a volatile organic compound (VOC) that is used as a solvent in a wide range of industrial, commercial and consumer applications. The primary use for perchloroethylene is to produce fluorinated compounds, such as hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs), as a solvent in dry cleaning, and vapor degreasing solvents.

Other uses include in a variety of commercial and/or consumer products such as automotive care products, cleaning and furniture care products, lubricants and greases, adhesives and sealants, paints and coatings. Source, Risk Evaluation for Perchloroethylene, Tetrachloroethylene (Perchloroethylene) - U.S. EPA retrieved 2020/02/22 original source: https://www.epa.gov/assessing-and-managing-chemicals-under-tsca/risk-evaluation-perchloroethylene

In February 2012, EPA released the final health assessment for tetrachloroethylene to the Integrated Risk Information System (IRIS) database. Tetrachloroethylene is a chemical solvent that is widely used for dry cleaning of fabrics, metal degreasing, and in making some consumer products and other chemicals.

An estimated 27,000 dry cleaners currently use tetrachloroethylene in the United States. It has been detected in ambient air in and near dry cleaning facilities as well as in adjacent residences.

Discharges of tetrachloroethylene from factories and dry cleaners can also contaminate groundwater and tetrachloroethylene has been found in drinking water. It is also found in the soil of about half of the Superfund National Priority List hazardous waste sites. - source Tetrachloroethylene (Perc) (Final, 2012) - - U.S. EPA retrieved 2020/02/22 original source: https://hero.epa.gov/hero/index.cfm/project/page/project_id/49/

Propane Gase Exposure Hazards

Fuknaga (1996) pointed out that actual poisoning gases from propane are rare.

Propane gas exposure hazard research

• Fukunaga, Tatsushige, Hidetaka Yamamoto, Akio Tanegashima, Yoshio Yamamoto, and Katsuji Nishi. "Liquefied petroleum gas (LPG) poisoning: report of two cases and review of the literature." Forensic science international 82, no. 3 (1996): 193-200.

Also see

• GAS APPLIANCE OPERATION at HIGH ALTITUDE
• GAS BTUH, CUBIC FEET & ENERGY
• METHANE GAS HAZARDS where you'll read that the principal risks are explosion (or fire) or asphyxiation.
• NATURAL GAS & PROPANE COMBUSTION PRODUCTS
• NATURAL GAS EXPOSURE HAZARDS

Propylene Gas Characteristics, Toxicity, Gas Exposure Limits

Propylene: "Propylene is a simple asphyxiant (that is, it acts by dilution of oxygen) and a rather poor anesthetic. Extremely high concentrations are required to produce any effect at all.

No TLV or PEL has ever been established for this material and NIOSH has not recommended a Standard. Its lower explosive limit is 2% in air (the upper is 11.1%) and a reasonable value for a maximum permissible concentration (suggested by Gerarde in Patty's Industrial Hygiene and Toxicology, vol 2, p. 1204, Interscience, New York, 1963) is 1/5 of the LEL or 4000 ppm. (Op. cit.) [25].

More details about exposure to propylene gas are

at PROPYLENE GAS HAZARDS

Sulfur Dioxide Gas Characteristics, Toxicity, Gas Exposure Limits

Sulfur Dioxide: "For sulfur dioxide, the TLV had been 5.0 ppm for many, many years, but in 1978 ACGIH announced its intention to reduce that TLV to 2.0 ppm; that was done in 1980. The reason for this was recent information indicating that chronic (long term, repeated) exposure to sulfur dioxide concentrations near 5.0 ppm was found to have some minimal effects on working populations. [26].

Sulfur dioxide is an upper respiratory tract irritant and acute (single or short-term) exposures cause nothing but irritation of the nose and throat. Long term exposures to sulfur dioxide concentrations in excess of 2.0 ppm can be expected in some cases to cause minor lung changes." (Op. cit.)

Sulfur dioxide exposure limits:

Watch out: NIOSH Immediately Dangerous To Life or Health Concentration (IDLH): 100 ppm

NIOSH REL: TWA 2 ppm (5 mg/m3) ST 5 ppm (13 mg/m3); OSHA PEL™: TWA 5 ppm (13 mg/m3)

More details about exposure to sulfur dioxide gas can be found at Sulfur Dioxide Gas.

Summarizing Sulphur dioxide gas exposure limits from OSHA,

• General Industry: 29 CFR 1910.1000 Z-1 Table -- 5 ppm, 13 mg/m3 TWA
• Construction Industry: 29 CFR 1926.55 Appendix A -- 5 ppm, 13 mg/m3 TWA
• Maritime: 29 CFR 1915.1000 Table Z-Shipyards -- 5 ppm, 13 mg/m3 TWA
• American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV): 0.25 ppm, 0.65 mg/m3 STEL; Appendix A4 - Not Classifiable as a Human Carcinogen
• National Institute for Occupational Safety and Health (NIOSH) Recommended Exposure Limit (REL): 2 ppm, 5 mg/m3 TWA; 5 ppm, 13 mg/m3 STEL

Sulfur Oxides Toxicity and Exposure Limits References:

Sulfur dioxide & other Oxides:

Air Quality Criteria for Particulate Matter and Sulfur Oxides, [PDF] Vol. III, US EPA, Environmental Criteria and Assessment Office, Research Triangle Park NC 27711, Dec. 1982, EPA-600/8/2-029c. Web search 08/26/2010, original source: http://nepis.epa.gov [large PDF]

Toluene gas exposure limits

NIOSH REL: TWA 100 ppm (375 mg/m3) ST 150 ppm (560 mg/m3); OSHA PEL: TWA 200 ppm C 300 ppm 500 ppm (10-minute maximum peak)

Toluene gas 5/b: gases which can be expected to be produced by fire, heat, or oxidation in commercial and residential properties. Toluol is a common contaminant produced by oxidized or burning carpets. [27] .

Trichloroethylene Gas Characteristics, Toxicity, Gas Exposure Limits

Trichloroethylene: NIOSH REL: 2 ppm 60minute CEILING during usage as an anesthetic agent and 25 ppm TWA during all other exposures; NIOSH considers trichloroethylene to be a potential occupational carcinogen as defined by the OSHA carcinogen policy [29 CFR 1990].
Current OSHA PEL: 100 ppm TWA, 200 ppm CEILING,
300 ppm 5minute MAXIMUM PEAK IN ANY 2 HOURS.

"Trichloroethylene is believed to have been discovered in 1864 and was first commercially produced in Germany in the early 1900s. It has been commonly used for cleaning of metals and other parts since the introduction of the vapor degreasing process in the early 1930s and continues to be the standard by which other cleaning processes are compared. Today, its primary uses are as an intermediate in the production of hydrofluorocarbon refrigerants and as a cleaning agent.

"The health effects of trichloroethylene have been studied extensively. The most significant findings to come out of the many long-term animal studies of the chemical are that it has caused liver and lung tumors in mice.

The significance of these tumors to human health is unclear due to species differences in both trichloroethylene metabolism and reaction to the metabolites. This is supported by epidemiological studies of workers exposed to trichloroethylene that generally indicate no overall increase in cancer risk.

Although recent studies of a small population of exposed workers in Germany appear to show an increase in kidney cancer, these studies suffer from major design flaws and are inconsistent with the results of larger, better conducted studies.

The International Agency for Research on Cancer (IARC) currently considers trichloroethylene to be "probably carcinogenic to humans" (Group 2A), based on its conclusions that there is "limited" evidence of carcinogenicity in humans.

The epidemiological data base for trichloroethylene is considered by the American Conference of Governmental Industrial Hygienists (ACGIH), however, to support classification in Group A5 (Not Suspected as a Human Carcinogen) "since the substance has been demonstrated by well controlled epidemiological studies not to be associated with any increased risk of cancer in exposed humans."

The U.S. Environmental Protection Agency currently is conducting a reassessment of the carcinogenic potential of trichloroethylene.
-- quoted from White Paper on Trichloroethylene http://www.hsia.org/white_papers/tri wp.htm

See Trichloroethylene - IDLH Documentation U.S. CDC NIOSH http://www.cdc.gov/niosh/idlh/79016.html

See OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force. http://www.cdc.gov/niosh/pel88/79-01.html

See OSHA's website of PELs - Permissible Exposure Limits http://www.osha.gov/SLTC/pel/

Vinyl Chloride Gas Characteristics, Toxicity, Gas Exposure Limits

Vinyl chloride gas exposure limits - may be a hazard in some building where vinyl products are present and exposed to heat, fire, or oxidation. [27].

Vinyl chloride: NIOSH REL: Ca; OSHA PEL: [1910.1017] TWA 1 ppm C 5 ppm [15-minute]

Also see:

• VINYL CHLORIDE HEALTH INFO
• VINYL SIDING or WINDOW PLASTIC ODORS

Volatile Organic Compounds (VOC's) and Mold-related VOC's, MVOC's:

VOC's gas exposure limits - are an outgas product of many substances such as paints, solvents, and in some cases, organic growths such as mold colonies. MVOC's refers to mold-generated volatile organic compounds.

There may be aesthetic or health-related complaints where VOC's or MVOC's are present. The absence of VOC's or MVOC's does not assure that problem molds are absent from a building, as the production of MVOC's by molds varies by genera/species and specific growth and environmental conditions such as changes in moisture or RH. Unless our report specifically states otherwise, our inspection and testing excluded these substances.

See our Guide to VOCs

at VOCs VOLATILE ORGANIC COMPOUNDS

Xylene Gas Characteristics, Toxicity, Gas Exposure Limits

Xylene gas gas exposure limits -

Here is some of the Xylene information on sources, environmental persistence, and toxicity from http://www.scorecard.org/chemical-profiles/html/xylenes.html .

Quoted material from the above web page is italicized below. We have edited for brevity and inserted a few comments. See the web link if you want to see all of the data in that report. The US EPA site info on this chemical is - http://www.epa.gov/oppt/library/pubs/archive/solvents/finlchr4.htm

Emissions of mixed xylenes have been detected from petroleum refining, motor vehicles, residential wood-burning stoves and fireplaces. Mixed xylenes are used as chemical intermediates, as solvents, in aviation fuel, and in household products such as aerosol paints and lacquers (Howard, 1990).

Xylene is registered as an insecticide. Only one product containing xylene is still registered, although use of this product has been suspended since 1993. It was registered for use on fruit, vegetable and grain crops, on ornamental lawns, gardens and plants. It may be applied to dogs, and animal dwellings as well as around houses and farm buildings (DPR, 1996).

The primary stationary sources [of Xylene] that have reported emissions of m-, o-, and p-xylene in California are manufacturers of motor vehicles and equipment, manufacturers of metal cans and shipping containers, and petroleum refining (ARB, 1997b). [Unless you're near a similar facility, we agree that looking at whatever common environment has been share by the two women you cite - not just in the home]

NATURAL SOURCES of Xylene

m- and p-Xylene occur naturally in petroleum. o-Xylene is found in coal tar, petroleum, forest fires and plant volatiles (Howard, 1990).

INDOOR SOURCES AND CONCENTRATIONS of Xylene

m-, o-, and p-Xylene are widely used as solvents and are present in numerous consumer products. Consumer products with the highest median emissions of xylenes include pens/inks and coatings. Xylenes are also emitted from building materials such as carpet adhesives, vinyl cove adhesive, latex caulk, latex paint, and various moldings. Environmental tobacco smoke is also a common indoor source of xylenes (Hodgson and Wooley, 1991).

ATMOSPHERIC PERSISTENCE of Xylene

The atmospheric lifetime of m-xylene is 14 to 15 hours. The atmospheric lifetime of o-xylene is 25 to 26 hours. The atmospheric lifetime of p-xylene is 24 to 25 hours (Kao, 1994).

HEALTH EFFECTS of XyleneL

Probable routes of human exposure to xylenes are inhalation, ingestion, and dermal contact (U.S. EPA, 1994a).

Non-Cancer: Exposure to xylene vapors may cause eye, nose, throat, and respiratory tract irritation. Xylene is a central nervous system depressant. Acute exposure may cause gastrointestinal effects such as nausea, vomiting, and gastric irritation. By analogy to toluene and benzene, xylene is predicted to cause cardiac arrythmias. Exposure may injure the kidneys.

In mice, rats, and rabbits, inhalation of mixed xylene or one of o-, m-, or p-xylene has resulted in increased post-implantation loss, reduced fetal weight, and other indications of retarded development. Oral exposure at high levels in mice has produced cleft palate and reduced fetal weight (ATSDR, 1993i; IARC, 1989c; HSDB, 1995).

Cancer: No information is available on the carcinogenic effects of mixed xylenes in humans. The U.S. EPA has classified xylene (isomers and mixtures) in Group D: Not classifiable as a carcinogen (U.S. EPA, 1994a). The International Agency for Research on Cancer has classified xylene (isomers and mixtures) in Group 3: Not classifiable as to carcinogenicity (IARC, 1987a).

Notice: the author a consulting professional member of the American Industrial Hygiene Association  - AIHA but not a certified industrial hygienist. Residential building investigations are not intended to certify any building as meeting government / industrial standards for workplace environments.

Similarly, the investigation and exposure level testing techniques specified by industrial and workplace standards may often be unsuitable for residential building environment and indoor air quality investigations.

Readers should be sure that the expertise and methodology used in building and contamination investigations are properly selected for the building type, occupancy, and likely hazards, and that adequate visual and technical inspections accompany actual tests for contaminants.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-06-28 by (mod) - what caused this gas leak and how long did it take to get this bad?

Joanne

Please see

GAS LEAK DETECTION, LP / NG

I will move our conversation and your photo to that page as it may invite helpful comment from other experts.

On 2020-06-28 05:43:43.625094 by joanne saho

hello i just had my gas safety checks done,

i had a bad leak,

can anyone tell me how long it takes for a pipe to become this bad please

On 2020-02-22

Susan

Please find your question and our detailed reply now found at

NATURAL GAS EXPOSURE HAZARDS

On 2020-02-22 by Susan

Hello, I recently had exposure to strong natural gas while "burning off manufacturer chemicals" from a thermador 48" gas range. Evidently it was a floor model that had been moved a lot and the gas pipe in the bottom of the small oven had been inadvertently disconnected from the main gas line coming into the oven which was causing a leaking blow torch in the bottom of my oven when turned on when I was told to burn off manufacture chemicals and that the smell was normal during the process.

It ran for 3 hours and the smell was very strong even though I had my vent hood on full force. I stayed in the room while doing this exercise because I was concerned something was wrong with the newly installed oven. When I insisted there was something wrong the company sent a technician who found this pipe disconnected. He said we were lucky it did not explode. I am now experience heart arrythmias and am wondering if the gas exposure may have contributed to them.

On 2018-04-03

Bob

Here is what Kidde says about your CO alarm test button
Peak Level Memory & Test Buttons on Your Carbon Monoxide Alarm
July 30, 2008

Any time you push the Test/Reset button the alarm will go through a series of test numbers that are programmed into the unit to test the internal diagnostics of the unit. This will start with a 888 reading, then display numbers usually in the 200 range, then back to 888, and lastly to zero. These are not actual readings, so you do not be alarmed or take action.

The Peak Level reading is just a memory. At one point the unit was exposed to something that caused the reading. It could have been a substance that was sprayed too close to the unit, paint fumes, or actual carbon monoxide that caused the reading.

To reset the peak level, push the Peak Level button, and hold it down while you press and hold the Test/Reset button for 2 seconds, then release them at the same time.

After this, monitor the unit for a few days to determine if this is a recurring problem or if it was an old reading. If you don't get a reading, then you know it could have just been a random reading and you have no other event taking place. If a reading does come back, reset the peak level again and start watching it every one to two hours, and try to narrow down when the reading is happening and be aware of what's going on around you (heat coming on or off, cleaning, etc.) to determine the source of the reading.

Key is this sentence

This will start with a 888 reading, then display numbers usually in the 200 range, then back to 888, and lastly to zero. These are not actual readings, so you do not be alarmed or take action.

SO once you have re-set your CO alarm if you continue to get CO detected there could indeed be a safety hazard in your home and prompt action and investigation would be appropriate.

If you are seeing 217 and assuming that Kidde's statement about the digital readout
"Digital Display: Displays the level of carbon monoxide the unit is sensing."

means that you are seeing 217 ppm of CO, that's significant in that normally, except for a typical burp of un-vented gas out through a flue damper when a gas fired appliance burner first begins to burn, we see virtually no CO in indoor air unless there is a problem with a fossil-fueled appliance

On 2018-03-30 16:08:44.183971 by Bob moore

My new Kidde Gas/CO is register 217 for gas. Is this a dangerous level?

On 2017-10-30 by Keith Ballard

at what level (PPM) is natural gas dangerous?

On 2017-01-18 by Pauline hing I inhaled natural gas

I inhaled natural gas when I was sleeping and now have itchy skin and head. This is 3 months later, what are symptoms and what is. Good treatment?

On 2016-05-04 by Darin Montague toxic gases coming into my apt on the first floor from the sewer.

I have been trying to get an indoor test for the toxic gases coming into my apt on the first floor from the sewer.it has caused me great illness and the city is ignoring me.

On 2016-02-09

Tom

There is no PEL-OSHA standard for R-22 but there is a TLV from the ACGIH of 25 ppm or 35 PPM STEL, and the LD50 (lethal dose 50%) is 2000 ppm/4H (rat)

Source: MSDS for R22 provided by GASCO Gasco Affiliates, LLC
320 Scarlett Blvd.
Oldsmar, FL 34677
TELEPHONE NUMBER: (800) 910-0051 24-HOUR EMERGENCY NUMBER: 1-800-424-9300
FAX NUMBER: (866) 755-8920
E-MAIL: info@gascogas.com
PRODUCT NAME: Freon R22 (Chlorodifluoromethane)
CHEMICAL NAME: Freon in air
COMMON NAMES/ SYNONYMS: R22
TDG (Canada) CLASSIFICATION: 2.2
WHIMIS CLASSIFICATION: A

On 2016-01-11 21:12:24.629611 by Tom Jones

Is there a PPM exposure limit for refrigerant 22?

Question: is it safe to stay in my building?

Great site. I would like to do a test to see if it safe to stay here or to understand whether I should move my family to a hotel while further tests are done. It is raining and our house smells strange and our noses are burning - Rosie 9/29/12

Reply:

Rosie,

To answer your question about the safety of remaining in a building where you susepect harmful gas exposures requires the help of a professional - provided there is some reason to believe that there is a hazard or risk and thus that it is cost-appropriate to hire someone.

A professional will perform a visual inspection of the building, conduct occupant interviews, may perform some general screening and IAQ tests, and depending on what is known about the building and its mechanical system, s/he may test for specific gases as well.

Watch out: If you believe that your building is unsafe for any reason, you should let the building owner/manager know immediately in writing and orally, and if there is an apparent immediate hazard: smoke, strong odors, fire, etc. it makes sense to evacuate first and call emergency services to check the building's safety.

Watch out: depending on the cause, a harmful gas may be present at inconsistent levels in a building. Also watch out for more basic hazards - like unsafe steps and rails, or biological or explosion or other safety hazards that can be present in any building.

...

Continue reading at GAS EXPOSURE SCREENING TEST or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

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• ODORS, Smells, Gases in buildings-Diagnosis & Cure tracking down and curing the source of odors or smells in buildings.
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