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The Regulatory Reform (Fire Safety) Order 2005 (RRFSO) came into law in 2006 and states that all fire exits must be kept clear and unobstructed, and that people must travel as short a distance as possible in order to exit the building in case of fire.
A fire exit door, or emergency exit, is basically the last door someone goes through to exit the building. It must be easy to open, well lit, clearly signposted, and also open outwards away from the building. Fire exits in poorly lit areas such as an internal corridor with no windows should also be marked with illuminated signs.
Fire rated escape doors
You’ve also got to consider internal fire doors on the escape route, as these doors must also be fire-resistant to 30 minutes to protect the route out of the building, be easy to open, and mustn’t need a key for access.
While you might think it’s obvious that companies should provide fire exits, it actually depends on the type and size of the building you have and how many people use the building as to whether you need a fire exit at all.
How many fire exit doors do you need?
Usually, a building would be expected to have a minimum of two fire exits, in case one is blocked by fire. However, if you have a very small premises, with few staff and only a short distance to travel to exit the building, it is possible that you only require one fire exit.
Where you do have two fire exits, both exits should be located well away from each other, so that there is no chance of both of them being compromised by fire, leaving no exit from the building. If this is the case, then a third exit will be required.
What size should fire exit doorsets be?
The Building Regulations specify the requirements for fire exits in a document called ‘The Building Regulations 2010, Fire Safety, Approved Document B, Volume 2 – Buildings Other Than Dwelling houses, 2006 edition, incorporating 2007 and 2010 amendments’, and from these regulations: for up to 60 people, a fire exit must be 750mm; for up to 110 people the exit must be 850mm; for 220 people the fire exit must be 1050mm; and for over 220 people, you must allow 5mm per person.
When planning for safe exit above the ground floor, it must be assumed that one of the exits will be blocked by fire and the largest fire exit must be disregarded in the calculations. This means that the smallest exit must be of sufficient size to easily evacuate all of the people on that floor.
According to British Standards, however, the number and size of exits depends on how many people you have in the building, what occupancy category the building has, and also what category the building has considering the fire growth rate.
If you follow this through, you can actually get to a calculation formula and work out exactly what is needed for your specific place of work.
In an A building, the inhabitants must be awake and familiar with the layout of the building, such as offices, factories, and workshops. This is likely to be the category for most businesses.
Category B covers museums, shopping centres, etc., where people are awake, but not necessarily familiar with the building and category C covers hotels, apartments, halls of residence, etc., where the residents may well be asleep if a fire breaks out.
Fire growth rates
Any of these categories may apply to businesses depending on the work carried out on the premises.
- Category 1 is considered slow, with limited materials that might feed a fire.
- Category 2 is medium, if there are stacked cardboard boxes
- Category 3 is fast, where there are plastic items in stacks or bales of materials
- Category 4 is ultra-fast, where there are combustible liquids (though this isn’t covered by British Standards)
These categories combined will give you what is called a risk profile, and from there, you can then calculate the size of the exits needed and how many fire exits there should be.
The absolute minimum size for an exit, according to British Standards, is 850mm, regardless of the risk profile.
For an A1 risk profile, the minimum width should be 3.3mm per person; for A2, B1 and C1, you’ll need to allow 3.6mm per person; for B2 and C2 the allowance is 4.1mm per person; for A3, allow 4.6mm per person, and for B3 and C3, 6mm per person must be allowed.
From here, the calculation can then be made:
If you add the maximum number of people per exit, taking into account the width and the risk profile, you can see if you have enough fire exits to cover the number of occupants in your building.
The minimum door width is 850mm and with an A2 category, you need to allow 3.6mm per person, so divide 850 by 3.6, which is 236 people.
If you have 3 fire exits, you must discount one of the exits as one way out of the building may be blocked by fire, so multiply 236 people by the 2 exits you can include, and you can evacuate 472 people safely.
If you have more than 472 people, you now know that you need to add additional fire exits.
This can be rather a tricky subject and so, if having read this, you still need advice, give us a call. If you now realise you do need to provide fire exits in your building, get in touch with us for high quality, easy-open, steel fire exit doors with push bars.