Threats to life in residential structure fires.

INTRODUCTION: Firefighters are taught that heat, oxygen deprivation, and carbon monoxide (CO) are the primary threats to life in residential structure fires, and they are taught to search for victims on the fire floor first, and then floors above. The objective of this study was to gather data regarding oxygen, CO, and heat conditions inside a realistic house fire, to examine the validity of these teachings.

METHODS: During six live-burn training evolutions in a two-story wood-frame house, metering for oxygen levels, CO levels, and temperature was conducted. Except where noted, all readings were taken 24 inches off the floor, to simulate the location of a crawling victim or firefighter. Readings were hand-recorded on a convenience basis by firefighters stationed outside the building, near the meters.

RESULTS: Of the 35 oxygen levels recorded, the lowest was 18.2%, with only 12 readings below 20%. Three of 16 first-floor readings were below 20%, whereas nine of 19 second-floor readings were below 20% (p=0.07). First- and second-floor readings were comparable (mean 20.3% vs. 19.9%, p=0.11). Except for one reading of 1,870 ppm, all CO readings at the ceiling exceeded the 2,000-ppm limit of the meters. Of the 34 CO levels recorded 24 inches off the floor, 29 (76%) exceeded the permissible exposure limit of 50 ppm, with the highest reading being 1,424 ppm, well above the "immediately dangerous to life and health" level of 1,200 ppm. None of the 20 CO levels recorded on the first floor exceeded the 30-minute exposure limit of 800 ppm, whereas seven of 14 second-floor readings exceeded this limit (p<0.001). While ceiling temperatures frequently exceeded the 1,000 degrees F limit of the meters, none of 16 readings taken 24 inches off the floor exceeded 137 degrees F. First- and second-floor temperatures were comparable (mean 88.5 degrees F vs. 90.1 degrees F, p=0.9).

CONCLUSIONS: In residential structure fires, CO poses a greater threat to victims and firefighters than does oxygen deprivation or heat. Emergency medical services personnel should consider CO toxicity in all fire victims. Conditions on the floor above a fire are at least as adverse as those on the fire floor.