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NOTE: This is an unformatted excerpt from our online fire protection training library.

Nature of Smoke

Temperature Effects

Thermal Tenability

Typically, a thermal tenability limit is suggested based on either hyperthermia or pain from skin burns. A temperature limit of 248oF (120oC) for dry air is used as a rule of thumb to determine which of these two possible effects will dominate (Purser 1988Purser 1988:
Purser, D.A. 1988. Toxicity assessment of combustion products. The SFPE Handbook of Fire Protection Enginnering, C.L. Beyler, ed., chapter 3. Quincy, MA: National Fire Protection Association.). Generally, exposure to heated dry air at a temperature less than approximately 248oF (120oC) leads only to hyperthermia. Pain from skin burns can be expected to be the dominant effect for dry air temperature greater the 248oF (120oC).

Thermal tenability limits are inversely proportional to the moisture content of the air. The temperature limit of 248oF (120oC) for dry air suggested to distinguish between the dominance of hyperthermia and skin burns is decreased to 176oF (80oC) for saturated air (Purser 1988Purser 1988:
Purser, D.A. 1988. Toxicity assessment of combustion products. The SFPE Handbook of Fire Protection Enginnering, C.L. Beyler, ed., chapter 3. Quincy, MA: National Fire Protection Association.).

Purser recommends the following relationship for the time to incapacitation based on averaging the time to incapacitation for exposures to humid air and dry air:

t = exp (C1 - C2T)                                              Example CalculationExample Calculation:
If an individual is exposed to 250oF smoke (assuming the smoke is an average of humid and dry air), how long before incapacitation?
t = exp (C1 - 2T)
C1 = 5.670
C2 = 0.0152
T = temperature of air, oF
t = exp [5.670 - (0.0152 x 250)]
t = 6.5 minutes
where,
t = time to incapacitation, min;
C1 = 5.670 (5.185);
C2 = 0.0152 (0.0273);
T = temperature of air, oF (oC)
NOTE: This is an unformatted excerpt from our online fire protection training library.

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