Moderate levels of CO can be hazardous
Chuck Herzog
Fire Chief
Manitowoc (WI) Fire Department
Recently, one of my lieutenants came to me and asked if we could increase the present CO maximum of 35 ppm under which we could operate during CO investigations. The request was prompted by knowledge that the alarms do not even sound until 100 ppm is present for 90 minutes and also by questions about “overkill” from other agencies who find us wearing SCBA.
My concern has always been the effects of CO on firefighters who may have to exert themselves heavily at a fire or other emergency shortly after a CO response. Several years ago, I read an article about the effects of CO on firefighters and created an overhead for use in training. Unfortunately, I cannot recall the source, but the overhead reads, “even moderate levels of carbon monoxide, 10 percent…, have been shown to lower the resistance of the heart to ventricular fibrillation. Smoke exposures may compromise the ability of the heart to cope…may have implications with regard to the high rate of sudden cardiac death among firefighters.” Concern about preexisting levels of carbon monoxide caused by exposure during a CO call and the potential effect on the health of our firefighters prompted me to adopt 35 ppm as the maximum.
In doing research to reconsider this standard, I came across a statement that I think might provide guidance to others contemplating this same question. In a paper entitled Health Effects of Carbon Monoxide, Michael A. Babich, Ph.D., of the U.S. Consumer Product Safety Commission, writes that “at 10 percent carboxyhemoglobin, there are no perceptible effects in healthy individuals–that is, no effects perceptible to the exposed subject. However, adverse health effects may occur at blood levels in the neighborhood of three percent COHb…. Electrographic changes and neurobehavioral effects may occur in healthy individuals…. Therefore, blood levels between three percent and 10 percent COHb may affect healthy, as well as sensitive, individuals.”
Later, he concludes, “In order to protect sensitive individuals, and to protect against chronic effects, CPSC`s Directorate for Health Sciences recommends against exposure to CO levels that would result in greater than about three percent COHb. This is equivalent to 15 parts-per-million (ppm) CO for 24 hours or 25 ppm CO for one hour. Similarly, the Environmental Protection Agency (EPA) National Ambient Air Quality Standard is nine ppm for eight hours, or 35 ppm for one hour.”
Frank C. Montagna (“Responding to CO Detector Activations,” Fire Engineering, January 1996) related that the threshold for requiring SCBA use varies throughout the country at this time. I think that this information, coupled with NFPA 1500`s requirement that breathing apparatus be worn whenever the atmosphere is hazardous or suspected of being hazardous, provides excellent guidance for those of us who must formulate safety policies for our people. Despite suspicions of “overkill” by other responders who may be less educated or who are never expected to exert themselves to the degree we must, I believe that a threshold of 25 to 35 ppm is in the best interests of our firefighters….
