The LWF Blog
Fire Safety Engineering for Design – Smoke Ventilation – Part 192
July 15, 2024 10:52 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 191, LWF discussed tenability criteria by talking about temperature and its effect on the human body. In part 192, we continue to discuss tenability criteria for smoke ventilation by looking at radiation and by starting to discuss visibility in smoke.
Radiant heat from the smoke plume or smoke layer can cause significant pain and injury to building occupants who have not yet evacuated a building. Pain is experienced at temperatures far lower than those required for piloted ignition.
For a prolonged period of exposure, the tenability limit for exposure of skin to radiant heat is around 1.7 KW · m–2. Levels below this value can be tolerated for long periods without affecting the ability of the person to effect an escape. Levels greater than this value are subject skin burning at a rate described by this equation:
tirad =1.33q -1.35
where tirad is the time (min) and q is the radiant heat flux (kW · m–2).
Visibility in Smoke
In conditions where smoke has caused low visibility, persons who are in familiar surroundings will be much better able to find their way to an exit. If they can see enough to confirm and maintain their orientation, they are likely to be able to evacuate safely.
A person in unfamiliar surroundings will need to be able to see exit signs or escape signage.
Of course, the addition of smoke to an area can affect even a familiar person’s experience when attempting to leave, causing confusion and disorientation.
A typical tenability limit for visibility in order to escape is around 8 – 10 metres. For the majority of fire types, this would cause some eye irritation due to irritants in the fire, but not at concentrations high enough to seriously affect escaping persons.
A person who is in very familiar surroundings, e.g. their own home, is likely to be able to carry out an evacuation even if the visibility is reduced to around 3 – 4 metres.
In part 193 of LWF’s series on fire engineering we will continue to visibility in smoke as part of the tenability criteria for smoke ventilation. 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.