Q1 (Total 25 marks).
A company is planning to build a four storey office building. The ceiling height will be 4m and the premises will be provided with a comprehensive fire alarm and fire detection system (Category L3).
Q1(a).
What are the maximum travel distances recommended for a single direction of escape and more than one direction of escape in the following documents:
ADB. (2 marks)
BS9999. (4 marks)
Q1(b).
According to ADB and BS9999, how many people could be accommodated by:
An 800mm wide exit. (2 marks)
A 1500mm wide exit. (2 marks)
Q1(c).
In 300 words or less, briefly discuss the differences between the results obtained from the two different documents. You should discuss how the approaches adopted by the two documents impact on travel distances and exit width in general for this type of premises. You should also state which approach you would recommend following to the company explaining your reasons for your choice.
(15 marks)
Q2 (Total 15marks).
The standard guidance of ADB recommends that the final exit from a stair should be at least as wide as the stair it serves.
A new assembly and recreation building has been constructed and there is an issue where the installed final exit from one stair is narrower than the stair it serves.
It is well established that the rate at which people flow down a stair is less than the rate of flow on a level passageway of the same width. Some international codes allow exit doors to have a lesser width than the stair (e.g. The NFPA Life Safety Code).
In theory, this should allow for the guidance of ADB to be varied provided that it can be demonstrated that an adequate flow rate can be maintained through a door with a narrower clear width than the stair width.
Q2(a).
Using the following information determine the maximum flow rate through the narrow final exit and compare it with the maximum flow rate down the stair. Is the restriction in final exit acceptable?
The calculations should be based around data from Nelson and Mowrer (See Annex G of PD 7974 Part 6).
Stair width = 1500mm.
Final exit width = 1400mm.
Stair tread dimension = 280mm.
Stair riser dimension = 175mm.
Population density will be less than 0.54 persons/m2.
(12 marks)
Q2(b).
What would be the minimum width of final exit that would not impact on the maximum flow rate down the stair.
(3 marks)
Q3 (Total 25 marks)
Q3(a).
In less than 100 words briefly explain what is meant by RSET and how does this approach vary from the approach in the prescriptive guidance of Approved Document B.
(5 marks)
Q3(b).
RSET comprises a number of different elements. Briefly discuss each of the following four elements and explain how they can be determined.
Detection time. (5 marks)
Alarm time. (5 marks)
Pre-movement time. (5 marks)
Travel time. (5 marks)
Answers on each element (i. to iv.) should be less than 100 words.
Q4 (Total 10 marks)
Using the information provided below, answer the questions on RSET. All calculations should be provided with an explanation/justification for selection of parameters where appropriate.
The building is a single storey open plan warehouse (with a simple layout) used to store building materials (which may include combustible materials).
The building has a comprehensive automatic fire detection and fire alarm system such that in the event of a fire it would be expected to be detected within 45 seconds.
A single stage alarm is utilised with no investigation period.
Fire safety in the premises is well managed and only trained staff are allowed onsite.
The occupant density is very low with less than 20 members of staff within the premises at any one time.
There are no disabled members of staff.
In the event of a fire, the maximum travel distance that someone could have to travel (taking into account the discounting of an exit) is 120m.
Q4(a).
What is the RSET for the warehouse?
(5 marks)
Q4(b).
The owner of the warehouse has decided to add a small mezzanine floor to one side of the premises accessed by an open stair. The travel distance from the furthest point on the mezzanine to the top of the open stair is 20m. Travel down the stair is 10m. Travel from the base of the stair to the final exit (taking into account the discounting of an exit) is 110m.
What is the RSET from the mezzanine?
(3 marks)
Q4(c).
If the premises is provided with a smoke ventilation system such that conditions at ground floor level could be maintained tenable indefinitely, what is the RSET from the Mezzanine?
(2 marks)
Q5 (Total 25 marks).
Answer below 5 sub-questions, using less than 150 words per sub-question.
What is ASET? Discuss the factors which affect its value.
(5 marks)
Explain the term tenability limit.
(5 marks)
Explain tenability based upon zero exposure.
(5 marks)
In cases where occupants could be expected to evacuate through smoke, one tenability limit is visibility. What are the recommended tenability limits for visibility? Why does it vary between small and large enclosures?
(5 marks)
In cases where occupants could be expected to evacuate through smoke another tenability limit is temperature. Discuss why the tenability limit for temperature in this case is often taken as 60°C.
(5 marks)