InspectAPedia ^®

This document discusses the toxicity and exposure limits for exposure to carbon monoxide gas (CO). We give references and explanation regarding Toxicity of Carbon Monoxide, based on literature search and search on Compuserve's Safety Forum. This is background information, obtained from expert sources. This text may assist readers in understanding these topics. However it should by no means be considered complete nor authoritative.

Seek prompt advice from your doctor or health/safety experts if you have any reason to be concerned about exposure to toxic gases. Carbon monoxide poisoning can be fatal but exposure at lower limits can produce flu-like symptoms and headaches that are often mistaken for ordinary illness. Readers of this document should also see HEAT EXCHANGER LEAKS.

IF YOU SUSPECT CARBON MONOXIDE POISONING GO INTO FRESH AIR IMMEDIATELY and get others out of the building, then call your fire department or emergency services for help. Links on this page also direct the reader to carbon dioxide gas information in a separate document. © 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.

Safety Suggestions: Install Carbon Monoxide Detectors in addition to Smoke Detectors

Carbon monoxide detectors are inexpensive and readily available, both as a battery-operated unit and as a unit that plugs into an electrical outlet in the home. No home should be without this safety protection, and homes with gas-fired equipment (natural gas or LP propane), space heaters, or other sources of risk should be extra cautious. Smoke detectors do not protect against carbon monoxide poisoning, and the opposite is also true. Carbon monoxide detectors do not warn of smoke or fire.

Guide to Inspecting Buildings for Visible Evidence of Conditions Likely to Produce Dangerous Carbon Monoxide Gas

The fact that you cannot see nor smell dangerous carbon monoxide gas does not mean that there is nothing to look for when assessing the safety of heating equipment. Not only are there easily spotted installation errors (the first list below), there may be more subtle but easily visible errors if you know what to look for (the second list below).

Visible building conditions risking carbon monoxide hazards

This is by no means the complete list of errors that can cause dangerous carbon monoxide exposure in buildings, but here are some common foul ups outside of the workplace that can cause dangerous levels of indoor carbon monoxide:

• Space heaters: improper use of gas or kerosene fired heaters can produce high indoor CO levels. Warning: Never go to sleep in an enclosed space with a space heater left operating. In addition to the CO hazards there is a risk of oxygen depletion which can also lead to asphyxiation.
• Gas fired central heating equipment combined with:
  • Improper venting, blocked, under-sized, over-sized, missing parts, improperly sloped chimney or flue. A variety of errors can cause a failure to vent combustion gases out of the building, allowing dangerous flue gases to build up indoors.
  • inadequate combustion air. If a heating appliance is installed in a small confined space it must be provided with outside combustion air. A service technician may tune and inspect a gas-fired boiler with the boiler room door open, finding that it seems to operate fine. When s/he closes it on leaving, there may be an inadequate or no opening for combustion air into the room.
  • Venting small appliances into large cold chimneys: Installation of small, higher efficiency gas-fired equipment into old homes at which the appliance is vented into a large (cold) masonry chimney. In such instances the heater may never develop sufficient heat and draft to actually vent up the chimney.
  • Also sometimes water heaters are left venting into a too-large, too-cold masonry chimney after a gas-fired boiler is converted to a high-efficiency direct-vent (no chimney) unit. One of my clients developed headaches every October - an event I traced to this condition in Poughkeepsie, NY. [DF re E.B. case 1988].
• Car exhaust, such as to occupants of rooms adjoining or even above a garage where car engines are left running
• Un-vented gas fired water heaters, often found venting directly into a basement utility room or even directly into a living area or bedroom.
• CHIMNEY INSPECTION GUIDE contains detailed suggestions for inspecting building chimneys including the detection of blocked chimney flues or indications that a chimney may be blocked.

Other clues which can suggest a risk of carbon monoxide hazards in buildings

• CO detector alarms Do not ignore this first line of defense. Install CO detectors near the heating equipment as well as in sleeping areas of the home. People have died after not believing their CO detector and taking out the batter to silence the annoying device which they believed was malfunctioning.
• Missing parts: Gas fired water heaters, furnaces, boilers which are missing flue vent connector components such as draft hoods and flue gas spill detection switches - it can be difficult to spot that something is missing unless you know what's supposed to be there. Review this topic with a trained heating service technician or plumber.
• Clogged heater draft hood from hair or other debris
• Signs of flue gas spillage Blocked flues will result in combustion gas spillage back into the building. Often this will cause:
  • Rust on heating equipment at the point of flue gas spillage - you can detect this even when the equipment is not operating
  • Rusty debris on the top of gas fired heating equipment below the draft hood
  • Water condensation on building surfaces may occur if gas-vented appliances are venting back into the building, especially on cool basement surfaces - you can only observe this when the equipment is operating
  • Odors of combustion products: while CO and CO2 are themselves odorless, if they are spilling from heating equipment, odors of other combustion products may be notices.

Testing for Carbon Monoxide

In addition to the installation of CO monitoring alarms in buildings, a variety of electronic and gas sampling equipment is available to make spot checks for hazardous gases. I have and have used a variety of these devices under a wide range of conditions.

While a "positive" indication of a gas is an important indicator of a hazard, a "negative" or "not found" result is nothing to rely on.

The fact that dangerous levels of CO are not present in a building at a particular instant is absolutely no guarantee that dangerous levels of CO (for example) may not occur even moments later. For example, opening a window, turning on a fan or clothes dryer, closing a door, and similar innocent acts can significantly change air flow, combustion air, and other building conditions.

Therefore spot tests for dangerous gases should not be relied upon to guarantee building safety. This is why the list of visual inspection items and proper heating equipment maintenance are so important.

Suggestions and content additions are invited. Contact me with items to add to these lists.

More Reading:
Heating System Check Recommended for Carbon Monoxide - CPSC Release 88-92

CHIMNEY INSPECTION GUIDE contains detailed suggestions for inspecting building chimneys including the detection of blocked chimney flues or indications that a chimney may be blocked.

MEDICAL EFFECTS of CO - Medical effects of Carbon Monoxide (CO) Poisoning

Many sources I (DF) reviewed indicated that if carbon monoxide exposure was subacute, that is if the person did not lose consciousness and was removed from the CO exposure before losing consciousness, then any medical effects were temporary. Indeed detection of CO exposure at a hospital is problematic since CO leaves the bloodstream quickly once a person is exposed to normal air. However there is evidence that lasting physical damage may occur from carbon monoxide exposure, though the popular press has not (2006) discussed the exposure level and duration necessary for these effects.

Heart muscle damage occurs from Carbon Monoxide (CO) exposure, screening recommended

31 January 2006 - The New York Times Science Section reports on a new study, released in JAMA's January 25 2006 Magazine Issue, and which indicated that people exposed to carbon monoxide suffer damage to their heart muscles and are at much greater risk for heart attacks in later years. The Times article asserted that CO Poisoning results in 40,000 emergency visits a year in the United States - the most common accidental poisoning event in the U.S. with an annual average accidental death rate of about 1000 people and average suicidal death rate of about 2400 people. [U.S. CDC] Five percent of such patients die in the hospital. Research was not cited regarding subacute exposures and exposures which do not result in a visit to a hospital. -- New York Times Science Section, January 31, 2006 p. F6, "After Crisis, Carbon Monoxide Still Takes a Toll."

The carbon monoxide exposure and heart muscle damage study was led by Christopher R. Henry, Minneapolis Heart Institute Foundation, in the current [Jan 2006] Journal of the American Medical Association The study examined the medical history of 230 people exposed to carbon monoxide and treated at hospital between 1994 and 2002, following their health to 2005. After 7 1/2 years, in this otherwise low risk (of heart failure) population, 25% of the originally-surviving patients had died - a rate about three times the average heart failure death rate statistic. For people who had suffered heart muscle damage the mortality rate was 38% with half of the mortalities being (apparently) traced to cardiovascular problems. The study concludes that people who are exposed to carbon monoxide should be screened for heart muscle damage. Heart muscle damage from CO poisoning (in the study) was characterized by elevated levels of cardiac troponin I (a type of protein) or creatine kinase-MB (a type of enzyme), and/or changes in diagnostic electrocardiogram (ECG). -- DJ Friedman paraphrasing the NY Times article and JAMA's news release regarding this study.

More references for this study:
see: Heart Injury Due to Carbon Monoxide Poisoning Increases Long-Term Risk of Death, JAMA January 25 2006. AMA news release 2006. This study was supported by an unrestricted educational grant from the Minneapolis Heart Institute Foundation. Study copies may be available from the JAMA/Archives Media Relations Department at 312/464-JAMA (5262) - mediarelations@jama-archives.org.

CO EXPOSURE LIMITS - Carbon monoxide exposure limits PEL and TLV set by OSHA and NIOSH

Carbon monoxide is a colorless, odorless, tasteless gas that, in its effects on humans, is a chemical asphyxiant - that is, it causes asphyxiation, or death by preventing a person from receiving adequate oxygen. When inhaled, carbon monoxide combines with hemoglobin in the blood more readily than oxygen does. Thus CO "displaces" or moves oxygen out from hemoglobin in the bloodstream. This interferes 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 carbon monoxide poisoning effects lead to a 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.

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 carbon monoxide or other gas exposure limit 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. Here are some other exposure levels and effects of carbon monoxide exposure from various sources:

Original document source

This carbon monoxide discussion file originated from a technical expert message board discussion on Carbon Monoxide and later Carbon Dioxide alarms, featuring comments by one of the leading authorities on CO, Jack Peterson, P.E., CIH, Ph.D., in May, 1987. NOTE: Daniel Friedman extracted CO and CO2 sections from that document, edited and added practical and field inspection-based information. Since its original publication this document has been expanded by reference materials from a variety of other sources.

Share this Article      

...

Technical Reviewers & References

Search InspectAPedia

• Daniel Friedman - principal author/editor of the InspectAPedia^® Website
• InspectAPedia Bookstore lists recommended books, organized by topic & available for purchase. Most of our articles also include a list of recommended books for the specific article topic as well as other references, and information sources.
• Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
• Additional technical contributors & reference sources for this article are listed below.

Use links just below or 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.

• 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 level, poisoning symptoms, & testing
• Carbon Monoxide Gas Toxicity hazard levels, poisoning symptoms, & testing
• 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.
• Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
• Sampling for gases in air such as VOC's, MVOC's, toxic chemicals, and combustion products.
  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.
• Radon Gas U.S. EPA Radon level maps
• Critique, contributions wanted: Contact Us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

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

• Our recommended books about building design, inspection, and repair, and about indoor environment testing, diagnosis, and cleanup are at the InspectAPedia Bookstore.
• ...

More Information on Building Diagnostic Inspections and Repairs

• Toxic Gas Exposure Hazards and Test Protocols including links to our toxic gas exposure screening and gas testing protocols.

InspectAPedia® Home & Site Map - Building & Environmental Inspection, Testing, Diagnosis, Repair, & Problem Prevention Advice: In-depth research & advice on diagnosing, testing, correcting, & preventing building defects & indoor environmental hazards. Unbiased information, no conflicts of interest.

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.

Building Inspection, Problem Diagnosis, Forensic Investigation & Testing, Repair Consulting

Contact Daniel Friedman for website content suggestions or for fee-paid consulting