At issue is the revised Underwriters Laboratories (UL) Standard 2034. This standard sets requirements that cover electrically operated, single and multiple station, CO detectors intended for protection in ordinary indoor dwelling unit locations, including: recreational vehicles, mobile homes, and recreational boats with enclosed accommodation spaces and cockpit areas.

If you have ever spent time on my Website,, or attended any of my presentations or seminars, you are very much aware of my severe criticism of UL-2034 and the flawed retail quality CO detectors manufactured to the various editions of that standard since its first publication on April 30,1992.

Since the very first version of UL-2034, I have been calling on industry professionals to:

1. Use the right sensors.

2. Monitor the sensors.

3. Have end-of-life warnings.

4. Improve digital display accuracy.

5. Reduce false alarms.

To understand my concerns for the poor quality of the UL-2034 listed CO detectors, it is important to understand the purpose and wording of UL-2034. The purpose is clearly defined in the foreword of previous UL-2034 editions. Consider Item 1.2.1 of the UL-2034 scope statement: "Carbon monoxide alarms [detectors] covered by this standard are not intended to alarm when exposed to long-term, low-level carbon monoxide exposures or slightly higher short-term transient carbon monoxide exposures, possibly caused by air pollution and/or properly installed/maintained fuel-fired appliances and fireplaces. See Table 38.1, Part B, False alarm resistance specifications."

Table 38.1.B indicates "NO ALARM" or Ignore levels: 30 parts per million (ppm) for 30 days, 60 minutes at 70 ppm, 10 minutes at 150 ppm, and 4 minutes at 400 ppm.

What is left unsaid in the foreword statement is the noticeably wide "time tolerance" permitted between the do not alarm and the must alarm levels. This is especially troublesome because the same manufacturers make CO detectors that meet the new EN-50291 Standard in Europe. The European standard requires all alarms to activate between 60 minutes and 90 minutes at 50 ppm.

Here are some conclusions drawn based on the wording of the standard:

  • At 30 ppm, a UL-2034 CO detector never has to alarm. (An additional note: Long-term exposure to low levels of CO can also have serious medical repercussions. Medical and professional expert opinions vary. General consensus, however, is that 10 ppm requires warnings, investigations, and action.)

  • At 70 ppm, it does not have to alarm until four hours of 70 ppm or higher.

  • At 150 ppm, it does not have to alarm until 50 minutes of 150 ppm, or higher.

  • At 400 ppm, it does not have to alarm until 15 minutes of 400 ppm, or higher.

    In my opinion the worst part about UL-2034, is that the standard would permit exposure to 65 to 69 ppm without alarming; forever.

    Fortunately, in March 1999, the Consumer Products Safety Commission (CPSC) took action and announced a recall of CO detectors that failed to comply with the standard to which they were manufactured. It was a step in the right direction.

    The overwhelmingly negative media publicity on the poor quality of the available retail-grade CO detectors caused a virtual standstill in North American sales. This slump was so severe that two Canadian manufacturers filed formal complaints against CTV, a local Canadian television news station. No retraction or settlement, however, was required. At that time, the two manufacturers were not using the right sensors and neither of the recalled CO detectors had an end-of-life warning indicating product sensor failure.

    Today, both manufacturers are using the proper electrochemical sensors and have end of life warnings.


    Thanks to additional studies and testing, product recalls, and new laws mandating the installation of CO detectors in residential buildings, people are becoming aware of the dangers of low-level CO poisoning and the need for stringent CO detector manufacturer guidelines. Canada has played a major role.

    Canadian interest in CO detectors greatly increased when Toronto decided to follow the lead of a few U.S. cities that had already written mandatory CO detector installation bylaws.

    This increased interest was further advanced when the Canadian Standards Association (CSA) acquired control of the International Approval Services (IAS) Laboratories, established previously by the merging of American Gas Association Laboratories and Canadian Gas Association Laboratories, and when the IAS wrote a greatly improved CO detector standard.

    The original IAS-96 Standard was the best CO standard ever written, resulting in extremely active competition between the CSA and UL. This original version proved to be so tough that only one manufacturer's detector could be listed. Unfortunately, IAS caved in to the pressure to dumbdown the standard, making it as weak as UL-2034.

    This increasing media attention prompted CTV to contact Jim Mackie, president of Fuels Safety Consultants and one of the world's leading experts, to do a series of professional, fully data logged, CO detector activation tests to verify compliance to the existing UL-2034 test requirements. These test results were alarming, revealing an extremely high percentage of compliance failures with the performance requirements of the standard to which they had been manufactured.

    In December 2004, I received a call from CBS News, N.Y., about the new mandatory CO requirements for homes in N.Y., and the quality of the UL listed CO detectors being required by the wording in the new ordinance. CBS indicated that it wanted to conduct its own tests on the CO detectors available in retail stores.

    I recommended contacting Paul Clifford of Mosaic Industries, or Mackie to perform the testing since they were both experienced CO testing professionals with no vested interests or stocks in any CO manufacturer. They chose Mackie. I was requested to be a witness to the procedures.

    Three days later the tests were completed, and I was happy to report that other than one CO detector that failed to alarm within the proper timeline, all of the CO detectors tested responded at the required levels of CO, within the required timelines.

    It appears that the CO detector manufacturers have gotten the message that the media, lawyers, and consumers are watching, and are expecting the CO detectors, as well as all of the detectors purchased, to do exactly what is promised, nothing less. In previous testing of UL-2034 listed CO detectors, failure to meet the required activations at the levels and time frames listed in the standard was 36 percent, 48 percent, or more. I applaud most of the CO detector manufacturers for finally meeting the UL requirements, as flawed as they are.


    I want to make it clear that UL-2034 is flawed. Even though improvements are being made, I do not endorse UL-2034. Like other positive changes occurring in the CO detector industry, these improvements are a direct result of the passion and dedication of a few life safety professionals, media attention (especially in Canada), and large, successful liability lawsuits.

    The mission now is to get UL and CSA to make the needed standards changes that will provide even greater protection for the consumer and for everyone in the home. I see a faint, dim light at the end of the tunnel, and I feel that it is time for a special thank you to a few dedicated professionals and the media who have made the light grow stronger.

    George Kerr is president and founder of CO – Experts, a division of G. E. Kerr Companies Inc. Kerr has been in the early warning detection industry since April 1953.

    Publication date: 03/27/2006