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Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment. Effects of Nitrogen Dioxide Gas Exposure in Buildings
NO2 Nitrogen Dioxide Toxic gas exposure limits & standards in buildings

What are the effects on humans of exposure to Nitrogen Dioxide - NO2?

This article seres gives basic information about exposure to and potential health hazards from a number of common toxic gases that may be found indoors or in or around buildings.

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Nitrogen Oxides Gas Exposure Effects & Hazards

The only oxides of nitrogen of concern in most industrial and commercial enterprises are nitric oxide (NO) and nitrogen dioxide (NO2).

The main source of both gases is combustion and only under special conditions are appreciable concentrations of nitric oxide formed. Nitric oxide oxidizes in air to nitrogen dioxide which is the more toxic of the two gases.

Nitric oxide, when inhaled, combines with hemoglobin to form nitrosohemoglobin, a carboxyhemoglobin-like material that rather rapidly is oxidized to methemoglobin.

That is, its main effect is to inhibit transportation of oxygen by the blood. Its TLV and PEL are both 25 ppm.

Nitrogen dioxide is a deep lung irritant. That is, this gas is not very soluble in water and thus is capable of penetrating deeply into the lung where it undergoes hydrolysis to other materials (acids) that are the actual irritants.

Because hydrolysis is a necessary condition for irritation and because hydrolysis takes an appreciable amount of time (several hours in many cases), nitrogen dioxide is known as a delayed-action lung irritant.

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 notable at 5 ppm and causes eye and nose irritation at 10 to 20 ppm. Currently (1987), the TLV 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.

WHO guidelines on NOx cited below and including results of animal testing discuss other hazards including including changes in lung metabolism, structure, function, inflammation and host defence against infectious pulmonary disease.

There are seven oxides of nitrogen that may be found in the ambient air. Nitrous oxide (N2O) is a greenhouse gas with significant anthropogenic sources contributing to its worldwide abundance (~ 0.3 ppm). However, nitric oxide (NO) and nitrogen dioxide (NO2) are the two principal nitrogen oxides associated with combustion sources.

Ambient concentrations of these two gases vary widely according to local sources and sinks, but can exceed a total concentration (NO + NO2) of 500 μg/m3 in dense urban areas. Nitrous acid (HONO) is a common pollutant in ambient and indoor environments, produced by the reaction of nitrogen dioxide with water.

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 Road traffic is the principal outdoor source of nitrogen dioxide. The most important indoor sources include tobacco smoke and gas-, wood-, oil-, kerosene- and coal-burning appliances such as stoves, ovens, space and water heaters and fireplaces, particularly unflued or poorly maintained appliances.

Outdoor nitrogen dioxide from natural and anthropogenic sources also influences indoor levels.

Occupational exposures can be elevated in indoor spaces, including accidents with silage and in ice arenas with diesel- or propane-fuelled ice resurfacing machines (3) and underground parking garages (4).

In ambient conditions, both outdoors and indoors, nitrogen dioxide exists in its gaseous form, and inhalation is therefore the major route of exposure at room temperature.

Exceptionally, direct contact with the eyes and associated membranes may lead to eye irritation, although this is more likely to occur in industrial settings after accidental contact with relatively high gaseous nitrogen dioxide concentrations (1). (WHO Jarvis ret. 2019)

Oxides of Nitrogen Gas Properties, Exposure Pathology, Symptoms, Treatment, Prognosis

The following information about exposure to ammonia gas hazards is based on information from U.S. Army Field Manual 8-285 Chapter 10, Noxious Chemicals:

Physical Properties of Nitrogen Oxide Gas

The term “oxides of nitrogen” applies to a mixture consisting of nitric oxide, nitrogen dioxide, and nitrogen tetroxide. Nitric oxide is colorless. The other oxides are red-brown gases.

Occurrence of Nitrogen Oxide Gas in Military Operations or Civilian Exposure

(1) The danger of nitrous fume poisoning is or cordite) are burned or detonated in poorly ventilation areas. This may occur in gun pits, armored vehicles, ship magazines, and turrets. This may also occur in mining and tunneling operations.

(2) In addition, nitrous fumes are emitted from fuming nitric acids (white and red) and are generated by the combustion of certain plastics.

Watch out: improper use of ozone generators to try to kill mold or odors may oxidize certain common plastics found in buildings, leading to the hazards discussed here. [OPINION-DF].

See OZONE HAZARDS

and OZONE MOLD / ODOR TREATMENT WARNINGS.

Pathology of Human Exposure to Nitrogen Oxide Gases

Inhalation of nitric oxide causes the formation of methemoglobin and does not appear to lead to any tissue lesions.

Inhalation of nitrogen dioxide results in the formation of nitrite that leads to a fall in blood pressure and to the production of methemoglobin. Inhalation of high concentrations of nitrogen dioxide (above 0.5 mg per liter) causes rapid death without the formation of pulmonary edema.

Somewhat lower concentrations of nitrogen oxide gas exposure result in death with the production of yellow, frothy fluid in the nasal passages, mouth, and trachea and marked pulmonary edema. The findings in other tissues are negligible.

Symptoms of Exposure to Nitrogen Oxide Gases

The symptoms following inhalation of nitrous fumes are due chiefly to nitrogen dioxide. The symptoms presented depend upon the concentration of the gas.

Exposures to higher concentrations cause severe local irritation with choking and burning in the chest, violent coughing, yellow staining of the mucous membranes, expectoration of yellow-colored sputum, headache, and vomiting.

Often, these early symptoms may be mild or entirely absent. After 2 to 24 hours, symptoms start with coughing, nausea, vomiting, frothy sputum, dyspnea, cyanosis, convulsions, and signs of lung edema. This train of symptoms may result in death.

At nitrogen gas exposures to very high concentrations for short periods of time, the onset of symptoms is very sudden and marked. Convulsions, unconsciousness, and respiratory arrest occur within a short time and death may follow rapidly.

Diagnosis of Nitrogen Oxide Gas Exposure

The diagnosis is made from the history, symptoms described, and sometimes the pungent odor of the gas or the yellow discoloration of the exposed mucous membranes.

Treatment for Exposure to Nitrogen Oxide Gas

Treatment of casualties with symptoms of pulmonary irritation is the same as for CG poisoning (chap 5).

Prognosis for People Exposed to Nitrogen Oxide Gases

The few cases with symptoms referable to the CNS either die quickly or, on removal to fresh air, recover spontaneously. Fatal cases usually die within 48 hours. Bronchopneumonia and varying degrees of pulmonary fibrosis and emphysema often follow recovery from the acute stage.

NOX Reference: Toxicity of Oxides of Nitrogen

WHO & Other Guidelines for Indoor Air Quality: Selected Pollutants found at NCBI:

 

Reader Question: on-site detection of NOx Nitrogen Dioxide Hazards Indoors

2019/04/15 John said:

COMBUSTION GASES & PARTICLE HAZARDS is a Good read BUT!

We talk a lot about CO and not about NOx. So you have CO spilling into room, would you not also have Nox splilling with it?

Therefore, could you not have more NOx ppm spilling than CO? Also, unless you have some $10K analyzer, say the more economical/popular field combustion analyzers like a Testo 310, 320, 327 or Bacharach units, NOx i not considered, it's filtered out.

So you can be getting sick and not know it cause it's not something that is tested for.

Reply: never rely on test instruments alone when checking for hazardous gases in buildings

Thanks for the comment, John.

Depending on the heating equipment and fuel you might get NOx (Nitrogen Dioxide) spilling into an interior space whether or not CO (carbon monoxide) hazards are present;

For other readers: the likely sources of NOx exposure in residential buildings include

It appears that the concern for NOx exposure is also in workplaces where NOX is in use in industrial processes.

Exposure limits for Nitrogen Oxide

NIOSH NOx EXPOSURE LIMIT: The recommended airborne exposure limit is 1 ppm, which should not be exceeded at any time.

ACGIH NOx EXPOSURE LIMIT: The recommended airborne exposure limit is 3 ppm averaged over an 8-hour workshift and 5 ppm as a STEL (short term exposure limit).

In the U.S. the New Jersey DOH has published this NOx exposure advice - for Nitrogen Dioxide
nj.gov/health/eoh/rtkweb/documents/fs/1376.pdf

And this WHO information source is helpful:

The salient question I raise about your question is: in a residential property where it is commonly recommended to have Carbon Dioxide detectors and smoke detectors installed, what's the added safety that would derive from adding NOx detection as well?

The answer is ... (thanks to Mark Cramer, Tampa) ... It depends - on whether the sources of indoor pollutants - (excluding roadway NOX) that are likely to be present - fuel burning appliances, are likely to produce hazardous levels of NOx *without* producing detectable levels of CO2 or Smoke.

That's a different question from yours.

Finally, I'd agree that IF there appears to be an IAQ complaint or if an expert is investigating building-related illnesses it would make sense to include both visual inspection and possibly testing for various harmful gases.

Watch out: depending on test instruments alone for the detection of dangerous indoor flue gas hazards is in my experience and view a bad and possibly fatal mistake.

Small changes in the building such as opening or closing a window or door, wind direction, or even exactly when a measurement is made or a test instrument is used can completely change the results.

Your $10K analyzer for NOx may find no hazard at the time of measurement.

One can for example use a Draeger gas detection tube for NOx at a cost of less than $10. per test.

RAE Systems Colorimetic Tubes (10 per box) - Nitrogen Oxides (NOx) cost less than $5. U.S.D. per test.

See details at COLORIMETRIC GAS DETECTION TUBES

Watch out: at HEAT EXCHANGER LEAK TEST we explain that small changes in the operating conditions of a gas fired appliance can make big changes in the detectability of flue gas leaks into building air .

Concluding that there are no hazards in a building based on such a test alone, without expert interview of occupant complaints, occupant observations, building history, building construction, materials, mechanicals, and without an expert and thorough inspection of the building and its mechanicals is unreliable.

Question: Odors in my home: I'm being stalked. Am I being poisoned?

(Oct 20, 2015) Kay Quinn said:
I have been stalked for 4 months. In the last 3 weeks an odor has appeared in the house that causes headaches and vomiting. Can this detect if I am being poisoned?

Reply:

Kay:

You first need to take this concern to your doctor. If she agrees that indoor environment conditions could be causing your symptoms you need an onsite expert to inspect and if appropriate test your home for possible causes. If your doctor believes it's appropriate, then an industrial hygienist familiar with residential hazards of a similar environmental inspector might be found

at CONSULTANTS & EXPERTS DIRECTORIES

To address your concern about being stalked, you should call your local police department for help and advice.

Question: I need help troubleshooting smells, poisons and toxics that may be in the walls of my home after a leak.

(Oct 23, 2016) Jill said:

My family & I have been sick for 2 months. My 10yr old daughter has suffered far more than the rest of us. No one could diagnosis her. Her eyes hurt,her body hurt,she had bubbles throughout her body & vibrations.

Throat pain,choking sensation, & the feeling of someone sitting on her. She was getting rashes & finally a doctor tested her for pneumonia. It came back positive. The day of her last dose her symptoms came back with a vengeance. Her eyes were way more painful, had floaters,flashes of lights/stars,on & on.

Doctors said anxiety. I began to get sick during all of this & thought anxiety for myself. My heart raced. Had chest pain & it worsened with activity. I began to think mold. My husband said maybe carbon monoxide. So I had the gas company out because we have since moving in,smelled poo.

Gas company found nothing. My husband has a meter that was picking up combustible gases so I called public utilities out. His meter didn't & told me I was paranoid. So my husband called a plumber friend. He said to run water through the vents for sewer gas. 1st one nothing. 2nd one drenched me. C

alled fire department & they said get out. Landlord is a weird guy. He came out though & knew exactly where to cut to fix the pipe. It was severed in half. We've been living in this house for 2 months & I homeschool so we rarely leave. The next day we returned to the house but immediately began feeling the same pain & symptoms.

We could still smell it too but th e meter wasn't picking it up. Oh-I found an neuro-ophthalmologist right before we had the discovery & she said my daughter has a traumatic brain injury. She said it can be caused by methane/carbon monoxide/gases poisoning. My lungs burn. Xray was clear but I hurt so much.

Questions: can the poisons stay in the walls/items even after the pipe was repaired? CDC seems to think so. And, seeing I am & my daughter is still experiencing symptoms after leaving, does it mean it's chronic? We are going to a neurologist but I know my lungs hurt so bad. She had bubbles that make me think that she had venous air embolism. I feel so blessed none of us died.

The sewer pipe was completely cut in half. My other 2 children also have symptoms similar to ours but are a little less severe. None of our symptoms are getting better even after a few days away. Like I said as soon as we reentered,it hit us so hard we had to leave.
Thanks for any help.

Reply:

Jill,

No one can safely diagnose a serious indoor environmental hazard simply by reviewing text. You need an on-site expert.

However I can say that in my opinion gases are not likely to remain long-term in a building once the gas Source has been found and corrected.

I should add a, however, that if there was a sewage leak or if there was another source of mold or indoor pathogens or contaminants such as particles or chemicals, those could remain in the building even after the original source has been removed. For example a sewage backup could leave hazardous bacteria and other pathogens and even hazardous heavy metals in the building.

The fact remains If You observe a strong odor as soon as you enter a building then almost certainly there's a source that has not been found and corrected.


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