But sometimes a building’s use may change and we may need to reconsider the suitability of the fire exits.
Examples of the times when we need to consider the suitability of exits are:
Where should you look for guidance?
There are a number of sources of advice for those in the UK. Although the Building Regulations apply to new buildings and alterations, they’re a good source of information. The Building Regulations Approved Document B covers the fire safety design of buildings in England and Wales. (In Scotland the equivalent is the Technical Handbook (Non-domestic) Section 2 – Fire and in Northern Ireland, NBS Technical Booklet E.)
Other places to look are the sector-specific guides to fire risk assessment issued by the Department of Communities and Local Government (and equivalents issued in Scotland) and BS9999, “Code of practice for fire safety in the design, management and use of buildings.”
What are the considerations?
In common with other sources of guidance on the subject, Approved Document B states:
The number of escape routes and exits to be provided depends on the number of occupants in the room, tier or storey in question and the limits on travel distance to the nearest exit.
There is a core principle that there should normally be at least two escape routes. However, exceptions are allowed where travel distances are short and numbers are low.
It wouldn’t be possible in a short article to explain every intricacy but taking an example of a single storey office, it could have a single entrance/exit provided the actual travel distance from the furthest point to the exit was less than 18 metres and there were less than 60 people using the office.
A note on “alternative exits”
As you’d expect, there are criteria as to what constitutes an alternative i.e. the routes must be more than 45 degrees apart (for a diagram, check out page 34 of Approved Document B).
The following table gives a general guide to the numbers of exits required by capacity:
| Maximum number of persons | Minimum number of escape routes/ exits |
|
60 |
1 |
|
600 |
2 |
|
More than 600 |
3 |
Recommended door width
Of course, it isn’t simply a matter of any old door does the job no matter what size, so as you’d expect there’s guidance on the design width of exits. Unfortunately, though, the available guidance differs greatly so that Approved Document B, for example, is not the same as BS9999 and is different again from the Department of Communities and Local Government (DCLG) guides. Here’s the table from the Approved Document B:
| Maximum number of persons | Minimum width in mm |
|
60 |
750 |
|
110 |
850 |
|
220 |
1050 |
|
More than 220 |
5mm per person |
In the DCLG guidance a 750mm door width in a normal fire risk premises has a capacity of 100 people and a 1050mm door can take 200. How do you decide which to use? Well, the Building Regulations apply to new builds and alterations, and the DCLG guidance applies to existing premises.
Where all the various guides are in agreement is that you should discount one exit, i.e. assume that a fire is affecting the largest of the alternative exits, and then make sure that the capacity of the remaining exits is sufficient. (If two exits are close together, you should discount both.)
Taking an example of an assembly room with a capacity of 200, you could fulfill the requirement of Approved Document B with two exits of a minimum dimension of 1050mm each or three at least 850mm wide.
Caution
Guidance should not be applied rigidly, so, for example, if there is a higher risk of fire or the occupants are at greater risk, then the acceptable travel distances reduce and you may need more exits. The most thorough way to apply these variances is to use BS9999, but it isn’t a document to cherry-pick from — you either apply the whole system to your fire strategy or leave it alone.
Answering the basic question how many fire exits we need in a building? I should say this depends on many factors. Some of them include the no of individuals on the building, the no of normal exits on the building, evacuation time to evacuate the building in case of emergency.
You’re right of course, the travel distances and directions given in the standards are an attempt to take these factors into account.
Evacuation time should be pretty swift – 6-10 minutes are targets I’ve heard. The amount of exits should be commensurate to allowing this.
Don’t get confused with the difference between rooms and buildings. The 45 degree rule only applies inside a room, however it is not that simple. The two exits cannot lead onto the same route, so two exits from a room may be more than 45 degrees appart but if they lead onto the same corridor and there is no seperation between the doors in the corridor it only counts as one exit. The reason being a fire in the corridor would knock out both doors. Outside the room you need to look at fire seperation, protected routes and places of… Read more »
Shame this article is headed up with signs which are now non-compliant. BS 5266 changed over a year ago and few people seem to know about the move back to BS 5499 type signs which comply with the new ISO 7010.
It’s only a visualisation to give the impression of the potential confusion over exits, not a recommended use of signage, but absolutely take your point, Mike, thanks for pointing this out.
Thanks for you comment, Mike, important advice. It’s also important that people remember there really is no hard and fast rule, and that risk assessments and simulations unique to a building are the best way to make sure you’ve covered the bases.
ISO7010 doesn’t make existing signs non-compliant however – just in case anyone interprets this conversation that way!
Thank you Claire. Very informative and to the point article. The only thing I would add there is that in the premises that are covered by the RRO (Fire Safety) and Building Regulations doors used as the final point of exit should be fire resisting. This is because fire started in the exit door area would effectively cut off the main escape route from the premises. If risk of fire is applicable to the areas located on both sides of the door, such as the entrance/exit doors of flats that are facing the common areas in HMOs, this means making it… Read more »
Following a guide tends towards compliance but does not guarantee compliance. The only way to ensure compliance is to carry out a risk assessment and deal with matters that arise from it. Even the building regulations require a risk assessment to be done. Blindly following the guides can be a disaster even when they are over-engineered to cope with most situations. The are so many variable factors which often change over time such that it would be impossible in a guide to cover all eventualities. Just taking the basic concept that 40 people can pass through a unit of exit width in one minute can… Read more »
Thanks Claire for an interesting article . There are so many factors to be considered for the provision of exits and any fire risk assessor of course knows that it’s a core principle of fire safety when commenting on means of escape. Article 14 of the FSO has many sub-sections to ensure that the escape routes and exits within a building are sufficient in type, width, number, location and that the exit doors are fitted with the correct door furniture and open in the right direction where necessary. I’m struggling with the comment posted that the final exit door needs… Read more »
I work at a petrol station and we only have one fire exit. The back door fire as been blocked off. If there ever a fire on forecourt we cannot get out as our only way out leads onto forecourt. Is that wrong.
I’ve been there 1 year and 4 month never had a fire drill training
I am appalled that the architects and owners and building department governing the Grenfell Tower approved a renovation that would remove a stairwell in order to add rentable space. How can this be permitted in the country that CREATED fire codes in response to the Great Fire of 1666?
Here is the scenario: You work in small office room that can hold up to 11 work stations. There is only one way in and one way out. No windows.Just the entrance and exit door. Now, a fire breaks out in the hallway of that door. you can’t escape because it’s right outside the exit door. What are you and your co-workers to do, there is no other way out of the office space??? No windows, no other exit door!!!!
Hey I know that you’ve discussed most of it in regards of the fire regs ..I was just wondering what is the typical distance from the room to the fire exits? I had various answers and so it made me confused.
My daughter is just renting a flat on top floor ,of a three story building . Is there a legal requirement for a fire escape ,as there isn’t one ?
Hi Joan. Sorry for slow response. .Did you find out about this? I know a fire safety expert who can give you advice if you need it…
This is some good information to know. I think that is our building, we don’t have enough signs. I’ll for sure let my boss know so that we can get some new ones installed as soon as possible.
What measures need to be temporarily taken when one exit (out of two) is out of use for a while due to repair works. In this instance in a private residential building with few residents who are very familiar with the building.
This will also depend on the travel distance to a place of safety.
the distance between exits horizontally – on level floor how is this worked out