Variations of Time-to-Incapacitation and Carboxyhemoglobin Values in Rats Exposed to Two Carbon Monoxide Concentrations

It has been suggested that passenger protective breathing equipment protect aircraft passengers from smoke for 5 min during an evacuation phase and for 35 min during an in-flight-plus-evacuation phase. Carbon monoxide (CO) is one of the most abundant smoke components and is the major threat in most fire atmospheres. Time-to-incapacitation (t sub i) is an end-point related to escape from a fire, and variations in t sub i measurements at specific CO concentrations have not been statistically documented. Therefore, variance in t sub i at two CO concentrations that produce 5- and 35-min t sub i in rats were determined; blood carboxyhemoglobin (COHb) saturation at t sub i was measured. Fifty male Sprague-Dawley rats were individually exposed to each CO concentration in a chamber equipped with a rotating cage, and t sub i was recorded as the time from insertion of the animal into the cage until it could no longer walk. In another set of experiments, blood COHb saturation was determined in rats exposed to these CO concentrations at stepwise intervals less than t sub i. At incapacitation and at the end of each exposure interval, rats were quickly removed from the cage and killed for blood collection and COHb quantitation. Values (mean + or - SD) for measured parameters were: For the 5- min t sub i study, CO = 5706 + or - 178 ppm, t sub i = 5.0 + or - 0.36 min, and COHb = 80.8 + or - 1.3%; for the 35-min t sub i study, CO = 1902 + or - 33 ppm, t sub i = 34.8 + or - 6.8 min, and COHb = 71.2 + or - 1.0% COHb levels tended to plateau prior to incapacitation Coefficients of variation for t sub i were 7.2% and 19.5% for the 5- and 35-min study, respectively.