Changes in the UL listings for Carbon Monoxide alarms

The UL 2034 listing requirements for home alarms are based upon CO concentrations measured in PPM and time of exposure. 

Carbon monoxide must be present in specific concentrations for specific times before they will alarm. 

This time weighted measurement standard has gone through at least two revisions with three versions (as of this 2/01 printing).

As a carbon monoxide source investigator, service technician, or other provider, you may encounter any one of the following three listings.

1.  April 30, 1992, UL 2034 listed CO alarms had to measure and alarm when CO is:

15 PPM for 8 hour before alarming, or

100 PPM for no more than 90 minutes before alarming, or

200 PPM for no more than 35 minutes before alarming, or

400 PPM for no more than 15 minutes before alarming.

During this time (prior to 10/95), many communities experienced an increased use of CO alarms by consumers, particularly Chicago.  First responders and Authorities of Jurisdiction had little experience with carbon monoxide measurements at these “low” levels.  There were some suspicions of the accuracy of these alarms and many encounters with CO alarm responses had the responders crying

“False alarm!”

We must examine and remember that CO concentrations outside of buildings in many urban areas will exceed 15 PPM for over 8 hours due to automobile influences.  We must also remember the early CO alarm responders most likely were using CO test instruments that auto-zeroed when turned on outside (inside or anywhere).  Others used the ‘stain tube’ type instruments which were not nearly as accurate or responsive.

Likewise, first responders who had instruments that allowed a ‘manually-zero’ of the instrument were doing so inside or close to their vehicles or outside of buildings in urban areas where back round readings of CO were not zero.

Consequently, many first responders or source investigators were starting with a false zero, thinking there was no CO in the atmosphere they started in, when in reality, there was enough to perhaps trigger the alarm.  Their instruments might not have shown but slight increases of CO upon entering those buildings, so they thought the alarms were inaccurate or defective.  Additionally, some of the home alarms sounded off at 9 PPM or lower before 8 hours.  This was and still is particularly troublesome for first responders in cities with high pollution.

Another important thing to know about this generation of CO detector is its’ response criteria for non-alarm status when selected vapors and gases are present in specific concentrations.  This Selectivity Test with these substances is intended to represent air contaminants likely to be found in the vicinity of an installed detector.

Methane                       500 PPM

Butane                          300 PPM

Heptane                       500 PPM

Ethyl Acetate                200 PPM

Isopropyl Alcohol         200 PPM

Carbon Dioxide          1000PPM

This low PPM requirement for Carbon Dioxide (CO₂) concentrations may have been another major contributing factor in many ‘nuisance’ alarms First responders and other CO source investigators most likely were not carrying any type of CO₂ measuring instruments that may have helped discover the cause of the alarm.

It is not uncommon to find CO₂ levels in residential buildings much higher than 1000 PPM.  Particularly given our efforts to save energy we seal up our homes and businesses.  Expired breath alone from occupants in a structure can easily result in a CO₂ build-up over 1000 PPM.

Additionally, unvented combustion equipment, like gas cooking ovens & burners, space heaters, fireplaces and others, dump tremendous amounts of CO₂ (and water vapor) into a space.  Under these circumstances, 2,000 to 3,000 PPM or higher of CO₂ in air is not uncommon.

Because of the seemingly high number of false alarms, much mistrust in this first generation of UL 2034 inexpensive home CO alarms resulted. Despite the number of false or what came to be termed ‘nuisance’ alarms, many lives were saved the misery or death from CO poisoning.

Also, many technicians, first responders, fuel suppliers, home inspectors and others began to examine & question their own practices and prejudices about carbon monoxide as well as codes, licensing, education and other aspects of their profession.  It seemed that many of the rules of thumb pertaining to CO had come about with little or no actual field-testing being performed and were being passed around as hearsay. 

Many who had been conducting CO and combustion testing prior to the home alarm invasion knew it was a real problem in the field. Their suspicions were that false alarms most often meant inaccurate testing by personnel who did not fully understand CO.  Nor were they looking at the building as a system.

2.  After Oct. 1995, UL 2034 listed CO alarms had to measure and alarm when CO is:

15 PPM for no less than 30 days, or

100 PPM for no more than 90 minutes before alarming, or

200 PPM for no more than 35 minutes before alarming, or

400 PPM for no more than 15 minutes before alarming, and

Alarms had to have a reset button that alarmed if 100 PPM or more is present for at least 6 minutes.  In essence, if the alarm sounded and the inhabitants of the building showed no sign of CO poisoning (nausea, passing out, general weakness of the body, etc.), they were instructed to enact the reset.  If it went off again, they were to vacate the building and call an Authority.  The selectivity Test criteria remained at their same levels.

3.  After Oct. 1, 1998, UL 2034 listed CO alarms must measure and alarm when CO is:

30 PPM for 30 days

70 PPM for no more than 240 minutes before alarming (may alarm as early as 60 min.)

150 PPM for no more than 50 minutes before alarming (may alarm as early as 10 min.)

400 PPM for no more than 15 minutes before alarming (may alarm as early as 4 min.) and have a manual reset that will reenergize the alarm signal within 6 minutes if the CO concentration remains at 70 PPM or greater.

Another significant change to the 10/1/98 CO alarm listing is the addition in the instructions stating that individuals with medical problems may consider using warning devices which provide audible and visual signals for carbon monoxide concentrations under 30 PPM. 

  For more detailed information on the concerns raised by the changes in the UL 2034 standards, go to George Kerr's website, coexperts.com .

Before you make a recommendation concerning CO alarms, it would be a good idea to know who is in the building.  Perhaps a more sensitive alarm with lower CO concentration settings would be more appropriate.

It must also be noted that Oct. 1, 1998 UL 2034 Residential CO Alarms must meet the specificity test referencing non-alarm status at specific concentrations of certain vapors and gases.  These concentrations include:

Methane – 500 PPM

Butane – 300 PPM

Heptane – 500 PPM

Ethyl acetate – 200 PPM

Isopropyl alcohol – 200 PPM

Carbon dioxide (CO₂) – 5,000 PPM. 

Please note that the CO₂ concentration was raised dramatically.  A 4,000 PPM increase is significant and should result in less CO₂ concentration caused alarms.  However, levels of CO₂ in the 2,000 to 4,000 PPM range can be harmful to even the healthiest of individuals and usually indicates lack of air change, combustion gas spillage or both.

We may still encounter buildings where these concentrations exceed these test limitations, particularly CO₂ buildup from lack of ventilation, improper use and placement of unvented space heating or cooking equipment, backdrafting or spillage from vented combustion appliances or systems.  Many of the buildings we enter have perhaps been over sealed to save energy.

Carbon dioxide (CO₂) is also measured in PPM.

Excessive CO₂ in air may cause illness symptoms similar to those of CO; like drowsiness, sinus stuffiness or breathing difficulty.  These symptoms can be compounded by warmer room temperatures.  A CO₂ and CO measurement upon entering buildings or rooms will give us immediate information about indoor air quality, safety and perhaps be vital to complete CO alarm investigations.

CO₂ LEVELS OF COMFORT IN PARTS PER MILLION

Normal outside levels                                                                350-450 PPM

Acceptable levels                                                                      less than 600 PPM

Increased complaints of stiffness and odors                               600 to 1000 PPM

ASHRAE and OSHA standards                                               1000 PPM

Increased complaints of general drowsiness                               1000 to 2500 PPM

Adverse health effects                                                               2500 to 5000 PPM

Maximum allowable concentration for 8 hour period      5000 PPM