IAFC issues additional guidelines for CO detector activation investigations
Carbon monoxide (CO) detectors using a semiconductor-type sensor can react to a high level of flammable gas as if it were CO, and responders to calls for activated CO detectors should routinely check for this condition, warns the International Association of Fire Chiefs (IAFC).
In its notice, the IAFC explained that such a situation is rare because the “rotten egg” smell of the odorant mercaptan suppliers add to flammable gas normally alerts people to a leak. The odorant, however, may get filtered out–as when the gas leak is underground and subjected to certain types of soil conditions–and permit flammable gas to reach dangerous levels without being detected. The gas concentration may grow unnoticed until it is ignited by an ignition source, such as a pilot light or spark from an electrical switch, commonly found in homes.
Semiconductor-type CO detectors do not respond to levels of flammable gas that may exist in homes from time to time, such as when there is a short exposure to vapors from an open can of solvent, the IAFC explains. However, if the gas concentration reaches an extremely high level, the detector may activate as it does for CO.
One fire department found a natural gas concentration of 10,000 parts per million (ppm), a level well below the product`s lower explosive limit (LEL) of 53,000 ppm, so there was no immediate danger of fire. However, the lack of odorant allowed the gas to gather unnoticed, and the level measured was high enough to activate the CO detector. The fire department discovered the gas as a result of its policy of routinely checking for flammable gas as part of its CO investigation.
Responders can easily check for flammable gas when using multigas meters for CO investigation; these meters normally have a setting for flammable gas as well as carbon monoxide, notes the IAFC. Responders using a single-gas detector that measures only carbon monoxide can use a separate combustible gas meter.
All detectors with semiconductor-type sensors are powered by 110 volts and must be plugged into the home`s electrical system. Battery-operated detectors use a different type of sensor that recognizes only carbon monoxide.
“Fire department detectors may not pick up any carbon monoxide; and as a result, we will assume the home detector is defective,” cautions Frank C. Montagna, a battalion chief with the City of New York (NY) Fire Department and author of “Responding to CO Detector Activations” (Fire Engineering, January 1996). “We may not vent because there will seem to be no need to. If the gas level should reach the LEL of 53,000 ppm, there is danger of explosion and fire.” The solution, he suggests, is to routinely check for flammable gas when a semiconductor detector registers the presence of carbon monoxide.
For additional information, contact Pat Coughlin, IAFC, (913) 268-1311, fax: (913) 268-5113.
