What benchmark of length for evacuation should be used

[Guest Bill-A-Bong]

Hi

We are a company on two floors with a warehouse adjoining the building, we have on average 21 people in the building at any time. When we do our fire drills we have been told to record the length of time each drill takes. How do I know if the length of time for our evacuations is acceptable? Is there a benachmark figure that we should be aiming for?

Thanks

[Tom Sutton]

There is no set time for evacuation; the post war studies originally came up with a figure of two and a half minutes for a traditional building which later was included in the guides for the Fire Precautions Act. These guides quoted 2.5 minutes from your workplace to a place of comparative safety, an enclosed area protected to a half hour fire resisting standard, and could be an enclosed corridor or staircase. Then 30 minutes in a comparative safe area to outside the premises and finally to the ultimate safe area, the assemble point, with no time limit).

Now we are in the age of risk assessment and we use available safe egress time (ASET) which is calculated in six stages,

1. Ignition to detection,

2. Detection to alarm,

3. Recognition time,

4. Response time,

5. Travel time,

6. Tenability limit.

Ignition to detection and detection to alarm will depend on the type of fire alarm you have, also if you do not have automatic detectors then training of your personnel will be important. Recognition time and Response time will again depend on training and if you have designated persons to initiate the evacuation. Travel time will depend on the distance personnel have to travel to reach safety. Tenability time is the time the escape routes will remain available and safe to use.

Escape time is the time from ignition until the time at which all the occupants of the building, or a specified part of the building, are able to reach a place of safety and this time should be less than ASET.

With only 21 employees in an office/warehouse situation you should easily be able to achieve escape time less than ASET and timing your evacuation drills will set a bench mark to check how effective subsequent drill are.

[Guest]

Take a look at the fire safety guides available from DCLG website. Do a google search for Fire Safety Guides Factories and Warehouses. Within that document 2.5 minutes is the evacuation time that your premises should be aiming for. For a building with your occupancy size you do not need to complicate thing with ASET calculations.

 

Good luck

[Tom Sutton]

On 2/9/2016 at 3:36 PM, Guest said:

Take a look at the fire safety guides available from DCLG website. Do a google search for Fire Safety Guides Factories and Warehouses. Within that document 2.5 minutes is the evacuation time that your premises should be aiming for. For a building with your occupancy size you do not need to complicate thing with ASET calculations.

Have you supervised an evacuation and timed the outcome, you are unlikely to achieve 2.5 minutes in most situations, what do you do then?

[George S. Lu, P.E.]

I would agree with Mr. Sutton.  Taking into consideration the ASET factors, one would easily arrive to a conclusion 2.5 minutes is too short. 

It is not possible to affirm a reasonable time as factors such as number of floors, occupant load, number of stairwells, and their corresponding width, all of which play a role in determining evacuation time.  To say there is a standard time would be harsh. 

I would think the local jurisdiction needs to agree on a reasonable time, and the engineers/architects then need to design the structure to meet this requirement. 

 

 

[Tom Sutton]

Thanks for your contribution George.

[Guest Josh]

BS9999 notes a 2, 2.5 and 3 minute evacuation timescale based on risk. That is a metric to use.

[Tom Sutton]

A 2, 2.5 and 3-minute evacuation in stage 1 has existed for many years and was the standard after the post-war studies, combined with the travel speed from the PWS, gives travel distances of 40 feet per minute in a fire situation, which equates as 80, 100, 120 feet to stage 2 (comparative  safety of a protected staircase or corridor) then 30 minutes to ultimate safety.

[Guest teacher]

For a high school of around 1,000 students ,faculty and staff, how long should it take to evacuate, line up, check roll ,and report?

[Tom Sutton]

I am not aware of any min/max evacuation times other than from places of risk to places of comparative safety, however I would hope the result of the roll calls would be available as soon as possible after the Fire and Rescue Service has arrived in case there are any persons missing.

[Guest Inspector III]

DOD Schools, Day cares and Youth Centers have two minutes to evacuate there facility, some up to one thousand strong and  they practice these drills monthly.  A good rule of thumb is start at two minutes and every additional story add one minute or go to the top floor furthest room from the exit and walk it then round up to the next minute.

[Tom Sutton]

Have you conducted a RSET and ASET to check out the theological time from the furthest classroom to a place of relative safety and then to ultimate safety. However the practical times most often bear little relationship and applied common sense is order of the day.