The LWF Blog
Fire Safety Engineering for Design – Smoke Ventilation – Part 191
July 8, 2024 10:20 amLWF’s Fire Safety Engineering blog series is written for Architects, building designers and others in the construction industry to highlight and promote discussion on all topics around fire engineering. In part 190, LWF discussed the tenability criteria for smoke ventilation system design, beginning with smoke hazards. In part 191, we continue discussing tenability criteria by talking about temperature and its effect on the human body.
There are three methods by which a person’s exposure to fire might incapacitate or kill them – heat stroke (hyperthermia), body surface burns and respiratory tract burns.
Hyperthermia may occur with a prolonged exposure of 15 minutes or more to elevated air temperatures that are too low to cause burns, due to a gradual increase in body core temperature to around 40 °C. Such cases may be referred to as simple hyperthermia and those experiencing it can be treated. Once the core temperature of the human body reaches 42.5 °C, the hyperthermia is usually fatal unless treated within minutes.
44 °C is the maximum temperature a person can bear for an extended period of time. Temperatures above this can result in pain and skin damage. The type and severity of the damage incurred will be dependent upon the skin temperature and the duration of time the temperature is elevated above 44 °C.
The hot gases from a fire can result in heat exposure and hyperthermia. The exposure of naked skin to temperatures above 120 °C result in skin pain and burns that may cause incapacitation. 120 °C may therefore be used in calculations as the upper tenability limit for direct exposure to hot combustion gases.
The temperatures indicated do not tend to take into account humidity in the air, but permitted exposure temperatures can drop to around 55 °C for wet smoke and 75 °C for dry smoke when exposure times are increased to up to 30 minutes.
It is suggested in NFPA 130 that thermal burns to the respiratory tract may occur when air is inhaled which is saturated with water, above 60 °C. This is, therefore, suggested as the tenable limit applied at head height where high levels of water vapour may be present (e.g. after sprinkler activation or during firefighting operations).
In part 192 of LWF’s series on fire engineering we will continue to discuss tenability criteria for smoke ventilation by looking at radiation. In the meantime, if you have any questions about this blog, or wish to discuss your own project with one of our fire engineers, please contact us.
Lawrence Webster Forrest has been working with their clients since 1986 to produce innovative and exciting building projects. If you would like further information on how LWF and fire strategies could assist you, please contact the LWF office on 0800 410 1130.
While care has been taken to ensure that information contained in LWF’s publications is true and correct at the time of publication, changes in circumstances after the time of publication may impact on the accuracy of this information.