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In addition to reviewing the gas exposure limits in this document, see Toxic Gas Exposure Standards - Summary for Indoor gases and also Indoor Gas Sampling Plan for Residential Buildings which lists many other toxic indoor gases which are among almost 300 toxic gases we can test for, depending on the building complaint, building conditions, and individual health concerns. Portions of this material are quoted from comments by Jack Peterson at a public CompuServe safety forum in 1989. At Volatile Organic Compounds VOCs we discuss several chemicals and gases found indoors and offer advice for reducing indoor exposure.

© Copyright 2009 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Potential Health Hazards of Exposure to Certain Gases

Hazard evaluation consists of comparing measurements of exposure (or dose) with exposures (doses) known to be safe or known to be hazardous. For the most part, because of biological variation, "no effect" levels are much easier to estimate than are "first effect" or other levels indicative of injury.

Of the several industrial hygiene standards-setting groups in this country, the most important and/or most quoted are the National Institute for Occupational Safety and Health (NIOSH), the Occupational Safety and Health Administration (OSHA), and the American Conference of Governmental Industrial Hygienists (ACGIH).

Only those standards promulgated by OSHA (called Permissible Exposure Limits or PELs) have the force of law; the others are advisory except that OSHA has claimed the power to force compliance with NIOSH "Recommended Standards" if it chooses to do so. The main advantage of ACGIH Threshold Limit Values (TLVs) is that they are reviewed and updated annually; neither NIOSH nor OSHA updates its standards with any regular frequency.

Health Hazards of some Gases, Jack E. Peterson, P.E., CIH, Ph.D., May, 1987

Ammonia Gas Exposure Hazards

Ammonia is very soluble in water and, in water, hydrolyzes to ammonium hydroxide, a strong base. These properties insure that ammonia gas is an upper respiratory tract and eye irritant. It dissolves in the water of mucous membranes (or tears), hydrolyzes and irritates rapidly mainly because of the high pH that results.

Because of this biological property of prompt irritation, most people cannot tolerate a concentration of ammonia in air sufficiently high to be harmful. Its warning properties assure a negligible hazard from ammonia inhalation if escape is possible. As with formaldehyde and other good upper respiratory tract irritants, people can become "hardened" to the irritation of ammonia and after several exposures can tolerate much higher concentrations than can an unexposed individual.

Under some circumstances, a hardened person can accept an exposure that will result in inflammation of the throat, bronchi, and possibly eyes. An exposure to 300 to 500 ppm for 30 to 60 minutes would cause such an effect and might be hazardous to health.

The current 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.

Arsine Gas Exposure Hazards

Arsine is arsenic hydride, the combination of arsenic metal and hydrogen gas. Arsine is a water-soluble gas. It is given off whenever freshly-generated hydrogen contacts metallic arsenic especially in an acid environment. As a lead-acid storage battery approaches full charge (in formation or boosting or simply charging), some hydrogen evolves. When arsenic is present in the grids of that battery, some arsine is formed and escapes through the vent caps. If the battery is seriously overcharged, much hydrogen (and arsine if a lead-arsenic alloy is used in the plates) may be given off; an ignition source can then cause the gases to explode.

The main acute effects of arsine on people are lung irritation and hemolysis (destruction of red blood cells). Both effects are usually delayed and do not appear until several hours after the exposure that typically occurs during the acid washing of a tank that has contained an arsenical slag.

Of the two, hemolysis is usually the more serious and is first indicated by pink or red urine that becomes darker with successive voidings. Debris from damaged red cells "clogs up" the kidneys, leading to extremely severe pain and, eventually, to a stoppage of urine flow. Because red cells have been destroyed, severe anemia results so that oxygenation of tissue is impaired. In addition, there may be severe lung irritation (impeding proper oxygenation of blood); death may result from asphyxiation a few days after the exposure.

These 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. Whether or not arsine has any chronic effects (such as the causation of cancer) is not known because there has been no study of people or animals chronically exposed to this material.

There are, therefore, no data available indicating that arsine is a carcinogen. Of the three "standards setting" groups, NIOSH is the only one that recommends extremely strict control (2.0 ug/cu. m as determined by 15-min samples) of arsine exposures.

All of the information upon which NIOSH based its Recommended Standard was (and is) available to anyone, including ACGIH and OSHA, of course. If half of the arsine inhaled is excreted in the urine (as seems to be the case for particulate arsenic compounds), then, inhalation of 200 ug/cu. m should result in a urinary concentration on the order of 666 ug/L. Under these circumstances, then, urinary arsenic concentrations might well be useful as indices of arsine exposure/absorption. However, there is very little data in the literature concerning urine concentrations resulting from measured arsine exposures.

Bromine Gas Exposure Hazards

Bromine is the only halogen that is a liquid at room temperature. Its color is a dark rust red as a liquid and as a gas. As opposed to the "upper respiratory tract" irritants and "lower respiratory tract" irritants, bromine is a "whole respiratory tract" irritant.

That is, its main effects are exerted on the deep lung and may be delayed for some time after the exposure, but it does have far better warning properties than do the lower respiratory tract irritants such as nitrogen dioxide, phosgene, and ozone. 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. Prolonged overexposure to bromine can cause dizziness, headache, and cough followed by abdominal pain and, later, lung edema and pneumonia if the exposure is severe enough. None of these signs/symptoms is at all likely, however, if irritation (eye or respiratory tract) is used as a warning to leave the area of exposure.

Carbon Dioxide Gas Exposure Hazards

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."

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.

As the carbon dioxide concentration climbs above a few percent, the concentration of oxygen in the air inhaled begins to be affected. At 6% carbon dioxide, for instance, the concentration of oxygen in air has decreased from 20.96 to 19.9%. OSHA has indicated that the lowest oxygen concentration for shift-long exposure is 19.5%, corresponding to a carbon dioxide concentration well above 60 000 ppm (6%). Carbon dioxide concentration, not oxygen concentration, is limiting in such circumstances.

Details about Carbon Dioxide Poisoning:See Carbon Dioxide Gas Toxicity hazard levels, poisoning symptoms, & testing

Carbon Monoxide Gas Exposure Hazards

Carbon monoxide is a colorless, odorless, tasteless gas that, physiologically, is a chemical asphyxiant. When inhaled, it combines with hemoglobin more readily than does oxygen, displacing oxygen from hemoglobin and thereby interfering with oxygen transport by the blood.

A person suffering from carbon monoxide (CO) intoxication may first experience euphoria (similar to the effect of a martini or two), then headache, followed by nausea and possibly vomiting as the concentration of carboxyhemoglobin in the blood increases.

To prevent these effects, OSHA has established a PEL of 50 ppm for an 8-hr exposure, identical to the TLV. NIOSH, on the other hand, has decided to be more conservative and recommends a standard of 35 ppm. All of these concentrations refer to exposures with durations of 8 hr/day, 40 hr/week for a working lifetime and all are attempts to establish a "no effect" level.

Details about Carbon Monoxide Poisoning:See Carbon Monoxide Gas Toxicity hazard levels, poisoning symptoms, & testing

Nitrogen Oxides Gas Exposure 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.

Ozone Gas Exposure Hazards

Ozone is a kind (called an "allotrope") of oxygen . It is formed in the ionosphere by the action of ultraviolet radiation from sunlight on oxygen. Lightning strokes are another natural source of ozone and the characteristic odor of that material can often be noted during and after a thunderstorm.

When pollutants are emitted into the air either by man or nature, almost all are eventually removed by one or more of several processes including reaction under the influence of ultraviolet radiation. One series of such reactions results in the formation of ozone as a "secondary" (formed by reaction in the air) air pollutant, often in rather high concentrations (several tenths of a part per million).

As ozone can be formed by nature's sparks (lightning), it can also be formed by man's. Whenever an electrical spark or corona occurs in air, some ozone is formed. This accounts for the characteristic odor noted near an operating electric motor such as an electric shaver.

Because ozone is found in so many places, its toxicity (ability to injure a living organism by other than mechanical means) has been investigated extensively since the early 1900s. Experimentation has shown that the odor of ozone can be detected and identified by most people at a concentration of from 0.02 to 0.05 ppm (parts ozone per million parts air + ozone). As the concentration increases to a few tenths of a part per million, the first effect noted is likely to be a feeling of dryness in the back of the throat. If a concentration on the order of 0.2 or 0.3 ppm is inhaled more or less continuously for several hours to a few days some lung irritation may result.

Higher concentrations of ozone can produce several kinds of toxic effects if exposures are sufficiently prolonged. Eye irritation (despite newspaper and TV accounts seemingly indicating otherwise) occurs only at concentrations high enough to result in other, more severe, toxic effects.

Ozone is a very reactive substance. It will readily react with just about any material capable of being oxidized, and with many that are not. The material with which it reacts may be a gas or vapor, a particle floating in the air (a mold spore, for example), or a solid (or liquid) surface. For this reason, when ozone is present in most enclosed spaces its concentration declines quite rapidly with time. Of course, if ozone is being generated more rapidly than it is destroyed by reaction, its concentration can build up. This is the main reason why devices that produce relatively large amounts of ozone are safe only in relatively large enclosures and why the ozone generation rate should be reduced in small enclosures.

Ozone is well known for its ability to eliminate certain odors. How this is accomplished is controversial. At concentrations just above the odor threshold, some odors do seem to vanish. The main reason for this may be ozone's ability to desensitize the olfactory apparatus so that the odors can no longer be perceived. Some evidence indicates that this may be the case at least occasionally. Other evidence indicates that ozone may react with the odor-causing substances, eliminating them from the air (this is probably the only mechanism that operates when concentrations are below the odor threshold).

Finally, some people have insisted that even if ozone does not paralyze the olfactory sense, its odor is such that it "masks" other odors. Perhaps all three mechanisms operate, each in its own area of effectiveness. As with all other materials, ozone has a dose-effect relationship with a threshold. That is, once the threshold dose has been exceeded, toxic effects are proportional to dose.

For inhaled gases, dose is proportional to both time and concentration. If the duration of exposures cannot be controlled (as is usually the case), then the concentration must be kept low enough so that no injury will occur even from prolonged and repeated exposures.

For ozone, that "threshold" concentration is 0.1 ppm. So long as concentrations are kept at or below that level, injury is not expected even in the most sensitive workers so long as their exposure durations coincide reasonably well with or are less than the 8 hr/day, 40 hr/wk regimen. This "threshold" level is accepted by the American Conference of Government al Industrial Hygienists (and is called the Threshold Limit Value by that organization) and by the Occupational Safety and Health Administration, OSHA.

The TLV or OSHA's Permissible Exposure Level (PEL) is not a fine line between safe and non-safe. Instead, it represents the best judgment of a group of experts of the highest concentration that can be inhaled repeatedly by a population of workers with no resulting injury. Higher concentrations may or may not have any particular effect on a specific individual.

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.

More depth: see Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous. Our complete list of articles about ozone can be found at these links:

OZONE as a "CURE" for TOXIC INDOOR MOLD
WHAT IS OZONE- O₃
OZONE AIR PURIFIER WARNINGS
OZONE HAZARDS
STANDARDS FOR OZONE EXPOSURE
TESTING FOR OZONE
OZONE TOXICITY
OZONE ODORS, MOLD, REFS

Propylene Gas Exposure Hazards

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.

Sulfur Dioxide Gas Exposure Hazards

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.

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.

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• Thanks to Alan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
• Portions of this data were extract5ed from CompuServe's SAFETYNET forum 1989 and from the following articles:
• [73766,1245] GASES.TOX 08-May-87 17240 53 Title: Toxicity & hazards discussion of various gases
• Keywords: Discussion of the toxicity and hazards of various gases, ammonia, arsine, bromine, carbon dioxide, carbon monoxide, ozone, nitric oxide, nitrogen dioxide, propylene, and sulfur dioxide.
• [74756,40] CO 20-Dec-86 7050 40 Title: Carbon Monoxide discussion by Jack Peterson
• This is a discussion of carbon monoxide from lift trucks, by Jack Peterson, in response to a query on the message board. Excellent information from one of the leading experts on the topic. ASCII file - Uploaded by Len Wilcox, 74756,40 [an old Compuserve address].
• [76701,115] COALAR.TXT 19-Aug-88 12814 17 Title: Message thread on Carbon Monoxide Alarms
• Keywords: CO CARBON MONOXIDE ALARM ALARMS MONITOR MONITORING TESTING
• [Portions of this file was excerpted and edited from contents of a 1986 Compuserve message board discussion on Carbon Monoxide alarms, featuring comments by one of the leading authorities on CO, Jack Peterson.-- DJF]

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Gases: Toxic gases, indoor exposure levels, testing, identification

• A Toxic Gas Testing Plan: A Gas Sampling Plan for Residential and Commercial Buildings lists some of the toxic indoor gases for which we test, depending on the building complaint and building conditions
• 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
• Carbon Dioxide Gas Toxicity hazard levels, poisoning symptoms, & testing
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• Formaldehyde: US EPA. UFFI (Urea Formaldehyde Foam Insulation) was previously considered a hazard (formaldehyde outgassing). Subsequent research virtually closed concern regarding this material; however formaldehyde appears to remain a health concern for sensitive individuals.
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  Unfortunately no single test or tool can detect all possible building contaminants. We use methods and equipment which can test for common contaminants. If the identity of a specific contaminant is known in advance we can also test for a very large number of specific contaminant gases in buildings. We use gas sampling equipment provided by the two most reliable companies in the world, Draeger-Safety's detector-tubes and Drager accuro™ bellows pump, the Gastec™ cylinder pump and detector-tube system produced by Gastec or Sensidyne, and we also use Sensidyne's Gilian air pump. For broad screening for combustibles and a number of other toxic gases and for leak tracing we also use Amprobe's Tif8850. All of these instruments, their applications, and sensitivities (minimum detectable limits) for specific gases are described in our Gas Sampling Plan online document.
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