How to Check Gas Piping, Controls, Regulators & LP Gas Tank Defects
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How to find & report defects found in LP or natural gas controls, regulators, or storage tanks
How to find & report defects found in gas piping inspections
Advice for changing from LP gas to Natural gas in a building
Advice for converting between Natural gas and LP gas in a building
Home inspection and Heating System inspection report language examples
Questions & answers about inspecting, testing, diagnosing, and repairing gas piping, gas regulators, and gas storage tank defects used with LP or natural gas burning appliances

Here we provide descriptions and photographs of unsafe gas piping, regulators, or controls on heating systems, indications of unsafe or improperly operating gas appliances, gas meters, and other gas installation defects. We also discuss the procedure for converting from LP gas or "bottled gas" to natural gas or "piped in gas" at a building.

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Unsafe heating appliance conditions caused by backdrafting are discussed at BACKDRAFTING HEATING EQUIPMENT. This document also provides free sample draft home inspection report language for reporting defects in oil and gas piping at residential properties.

General safety warning: improper installation and even improper inspection and testing methods involving natural or "LP" gas can involve dangerous conditions and risk fire or explosion. If you smell gas you should leave the building immediately and should do so without doing anything that could create a spark such as operating a light switch or telephone.

From a safe location, call your gas company's emergency line and/or your fire department. The text provided here is a working draft and may be incomplete or inaccurate. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution. Also see How to Report Defects in Oil Piping. NOTICE: while example report language is provided here, reproduction of this or any of our web pages or their contents at other websites or in printed documents for sale is prohibited.

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Immediate LP Gas & Natural Gas Safety Hazards

Immediate LP or natural gas safety hazards: if there is evidence of an LP or natural gas leak at a building, gas odors, for example, you should:

Do not do anything that is likely to cause a gas explosion, such as lighting a match, operating an electrical switch, or even using a telephone in the building
Leave the building immediately and keep a safe distance away - 100 feet or more.
Notify other building occupants of the safety concern
Contact the local gas company and/or fire department

Heating equipment which the inspector (or building occupant or manager) judges to be an immediate life safety hazard should be shut down and appropriate emergency services called. See Gas Leak Detection for leak detection procedures and alternatives.

What to Do if You Smell Gas

*** Immediate LP Gas or Natural Gas Safety Concerns:

Gas Odors: A gas leak can be indicated by gas odor such as in the utility area near appliances or elsewhere in the building.

Here is a list of examples of other immediate LP gas or natural gas leak safety hazards that might be detected using a TIF8800™ Combustible Gas detector or using a soap solution and bubble testing:

A gas leak in gas piping - check particularly at piping joints or in areas where there is apparent damage, corrosion, possible pin holing in the piping.
A gas leak at the gas meter equipment. Check at meter seams and at piping connections.
A gas leak at the gas control valve.
- A gas leak may be found at the appliance pilot and temperature control knobs at control top.
- A gas leak may be found at the center seam along the RH side of the control. (often on gas fired water heaters we can detect a very small trace leak of LP gas or natural gas at the side seams of the control; beware: volatiles in pipe dope or in valve label glue might also cause the TIF8800 to indicate that a leaking gas is present).
A gas leak may be found the gas line shutoff valve.
A gas leak may be found the appliance pilot line at the control.

You should have your plumber test/replace any suspect gas controls promptly. Replacement of a control itself should not involve significant expense. This repair should not be deferred. You should be sure that building occupants know if this or other unsafe conditions are present.

How to Identify the LP Gas or Natural Gas Fuel Source

Natural gas is supplied by the utility company through piping, usually buried in the street in front of or behind the building, and entering the building through a gas meter which is located outside or at older installations, possibly inside the building.

Our photo (left) shows a gas meter installed indoors in a building utility basemen.

LP Gas or "bottled gas" or liquid propane gas is supplied (usually) by a local LP gas distributor who fills an LP gas tank located on and serving the building.

The LP gas tank may be above ground (usually at a building exterior wall) or it may be buried at the property. Our photo (left) shows a rather large outdoor aboveground LP gas tank.

Natural gas and LP gas appliance compatibility

These two fuels are similar in that both are used to provide energy to home heating systems and other appliances but they have some different properties of operating gas pressure, weight, method of distribution, and chemistry. Most gas appliances are delivered already set up to use either natural gas or LP gas but not both.

Most gas appliances can be converted from one fuel to the other - what is involved may be simply changing gas metering orifices in the equipment (for example at the burners on a stove) or it may also be necessary to change or adjust a gas regulator located inside the appliance.

Watch out: Do not hook up an LP gas-ready appliance to a natural gas supply nor can you connect a natural-gas ready appliance to an LP gas supply without reviewing and acting on the manufacturer's instructions for converting the appliance from one fuel to the other. It is virtually always the case that some equipment adjustments and changes are necessary to switch between natural gas and propane gas.

As JR, an industry manager familiar with gas pressures pointed out, these two fuel gases operate at different pressures. In residential appliances

Natural Gas system pressure: Natural gas operates at a nominal pressure of 7” WC (about 0.253 psi)
LPG or Liquid Propage Gas system pressure: LP gas or propane operates at a nominal pressure of 11” WC (about 0.397 psi)
Actual NG or LPG gas pressures vary: [Note: the exact pressure you see in the building at an appliance may vary from these numbers depending on the gas distribution piping system size, diameter, number of appliances served, number of appliances operating, regulator adjustment, and other factors. See Gas Regulators for Appliances and Gas Regulators for LP Tanks. See LP or Natural Gas Pressures for a table showing the range of variation in LP gas pressure in the tank at various temperatures. - Ed.]

If you are planning to convert from one gas fuel to another, such as from LP gas (bottled gas or liquid petroleum gas) to piped in natural gas, see our advice and safety warnings at Gas Conversion LP Natural Gas.

What Chemicals are Used to Produce the Characteristic Odors in Natural or LP Gas?

Mercaptan gas odorant components, concentration strength, human exposure levels

Mercaptan is, according to our industry commentator J.R., a widely-recognized odorant, but only one of a number of similar-smelling products that are added to natural gas or bottled gas to assist in recognizing that a dangerous gas leak is present since natural gas alone, CH₄ (Methane) is odorless.

The product added to natural gas to provide it with a characteristic odor is a mixture of tertiary butyl mercaptan, dimethyl sulfide and n-hexane.

Commonly in the trades the gas odorant product is just called "mercaptan".

Mercaptan is added to natural gas at a rate of 0.08cc’s/1.0 m3 of natural gas.

Therefore very little mercaptan (or other gas odorant chemicals) in the gas stream.

Gas odorants are produced by Odor-Tech, a subsidiary of Arkema, by Chevron Phillips Chemical, and others. Odor Tech also produces Mercaptan Assassin ESD - an odorant-blend kit used to clean up mercaptan spills.

Critical Hazard Limits for Natural Gas or LP Gas

According to J.R., one of our industry correspondents, odorants need to be detectible in the natural gas at 1/5 the lower explosive limit (LEL), or more properly, the lower flammable limit or LFL.

So this is the amount of natural gas required in the test.

A person is exposed to very little natural gas in the air by the time they smell it.

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GAS PIPING, VALVES, CONTROLS
  Gas BTUH & Cubic Feet
  Gas Conversion LP Natural Gas
  Gas Flame & Noise Defects
  Gas Igniter Defects, Repairs
  Gas Leak Detection
  Gas Lighting Pipes & Fixtures
  Gas Meters
  Gas Piping Defects
  Gas Regulators for Appliances
  Gas Regulators for LP Tanks
  Gas Regulators, Two Stage
  Gas Shutoff Valves
  LP Gas Tanks
  LP & Natural Gas Safety Hazards
  LP & Natural Gas Pressures
  METHANE GAS SOURCES
  Natural Gas Combustion Products
  Types of Fuel Gas Source

U.S. Energy Information Administration - eia.doe.gov/
U.S. Environmental Protection Agency - epa.gov/solar/energy-and-you/affect/natural-gas.html
At Natural Gas.Org www.naturalgas.org/environment/naturalgas.asp#emission you’ll find a table of combustion products
At geocities.com/rainforest/6847/report1.html is an interesting and detailed though not “neutral” report on the components and contaminants in the combustion of natural gas. You’ll see a long long list of emissions products, but look again – most of the contaminant levels listed are in the picograms.
apvgn.pt/documentacao/iangv_rep_part1.pdf lists the components in natural gas exhaust from vehicles
The Need Project, Manassas, VA: need.org/needpdf/infobook_activities/SecInfo/NGasS.pdf
Kroschwitz, Jacqueline I., and Mary Howe-Grant (eds.). "Gas, Natural." In Encyclopedia of Chemical Technology. 4th ed., vol. 12. New York: John Wiley and Sons, Inc., 1993.
Tussing, Arlon R., & Bob Tippee. The Natural Gas Industry: Evolution, Structure, and Economics. 2nd ed. Tulsa, OK: PennWell Publishing, 1995.
Thanks to reader E Leal for suggesting the addition of details about how to convert gas burning appliances from propane to natural gas or from natural gas to propane. 8/4/09
Thanks to reader JR for discussing LP and natural gas operating pressures and leak detection safety, October 2010.
Odor-Tech, 7591 Esler Field Road, Pineville, LA 71360, Tel: 318-767-0821 4is a subsidiary of Arkema, and has offices throughout the world. Email: arkema.phil-oc-customer-service@arkemagroup.com.
Odor-Tech products include
Spotleak® blends for natural gas odorization
Ethyl Mercaptan for propane and butane odorization
Tetrahydrothiophene
Mercaptan Assassin
Chevron Phillips Chemical, 10001 Six Pines Drive, The Woodlands, TX 77380, Tel: 832-813-4100, 800-231-1212 (Toll free, within the US) a has offices throughout the world and producesolefins, polyolefins, aromatics, and styrenics as well as other specialty chemicals and plastics.

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.

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Immediate LP Gas & Natural Gas Safety Hazards

What to Do if You Smell Gas

*** Immediate LP Gas or Natural Gas Safety Concerns:

How to Identify the LP Gas or Natural Gas Fuel Source

Natural gas and LP gas appliance compatibility

What Chemicals are Used to Produce the Characteristic Odors in Natural or LP Gas?

Mercaptan gas odorant components, concentration strength, human exposure levels

Critical Hazard Limits for Natural Gas or LP Gas

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair