Exit width

[Guest MatMoore]

Good Afternoon, What do you class as '1 Unit' in your calculation of Exit widths ?

[Tom Sutton]

The purpose of this concept is to allow you to understand the basics of means of escape and not how to design a means of escape from fire. There are many considerations, in planning means of escape, but it will give insight in how a means of escapes are designed. It is based on the old prescriptive concepts but understanding these principles will help in understanding the modern risk based methods.

Discharge rates.

In a real life-threatening situation, this obviously causes more rapid response. Discharge in conditions where the crowds are not in immediate danger and are well disciplined may not show great urgency and can lead to low discharge rates. Many assessments of this rate of flow have been made following tests, (particularly those using Paris firemen in 1938 and 1945 and the London underground). The generally accepted rate is 40 persons per minute per unit exit width. It should be noted here that the figure of 40 per minute was an average figure while the actual figures varied between 20 and 170.

Unit Widths.

The width of a unit corresponded to the average shoulder width and was determined at 525mm. Two units of 525 (i.e. 1050mm) were required for 2 people to travel through, shoulder-to-shoulder. However, due to overlapping effects, further units of width required were found to need only another 450mm. Hence, 3 units of 525 + 525 + 450 = l500 mm and 4 units of 525 + 525 + 450 + 450 = 1950mm. Units greater than 4 units wide were considered to slow flow rates down, and so the maximum width of an exit is 4 units or 1950mm.

Another consideration is the average widths of people today compared with 1938 and 1945, it is most probably wider another reason one should use modern day guides.

[Guest BBaiki]

Good Morning,

I am having a house built in Northumberland and the current plan of the kitchen/breakfast rooms show that the access gap between the kitchen and breakfast room areas is only 600mm. This does not seem to provide an adequate escape route gap in the event of a fire and precludes disabled access into the kitchen area. Can you please let me know if there are any legal requirements for minimum exit widths? (I know there is a non-domestic situation) and if there is no legal minimum what exit width would you recommend.

Thank you

Brian

[Tom Sutton]

I would suggest you check out Approved Document M at http://www.planningportal.gov.uk/buildingregulations/approveddocuments/ that is the guidance for access to and use of buildings. You need 2.8 page 25/26.