45 degrees rule

[lyledunn]

Consider a room that is required to have 2 MOE. The room is rectangular and has an occupant capacity of120. Wherever the angle is less than 45' persons can move to a point in the room from which the angle is 45 plus 2.5 degrees for each meter travelled and still have exits reachable within 18m.
Is this correct interpretation?

[kurnal]

The travel distance where there is less than 45 degrees etc should not exceed 18m and this distance is added  to the total travel distance to the nearest  storey exit , the total  combined travel distance should not exceed that permitted for two way travel

[nearlythere]

The angle of divergance rule can be confusing but essentially simple with the explanation best left until at least 3 days after St Patrickles Day.

[Phoenix]

I understand that you still have the additional 2.5 degrees for every metre travelled in NI but we don't bother with that in England and Wales (or Gibraltar).  Don't know about Scotland.  It shouldn't be referred to as the "45 degree rule", it should be referred to as the "45 degree rule of thumb" because it is certainly not a "rule" but it does give a simple means that can assist the assessment of the adequacy of escape routes.

Bearing that in mind, if you forget the additional 2.5 degree element, the following diagram shows the parts of a room where the two exits are less than 45 degrees from each other (the shaded areas).

There are two conditions that have to be met:

1. No part of the shaded areas should be more than the single direction limit from the un-shaded area (via routes that can be walked),
2. No part of the room (shaded or un-shaded) should be more than the multi-direction limit from the nearest exit (again, via routes that can be walked).
(Basically, what kurnal said.)



The curves are rather complex and my diagram is only a rough representation of the shapes of the curves.  To try and incorporate the additional 2.5 degrees into the diagram would probably make my head boil.  No one should ever try to work out precisely where these curves lie in a real room (it's not worth the effort), they should just make approximations based on the layout as they find it.

To demonstrate the rough nature of this rule of thumb here are two more diagrams.  In the first diagram the two escape routes from location A are less than 45 degrees apart and so we treat this as one escape route until the angle between routes becomes greater than 45 degrees.



In the second diagram the two escape routes are more than 45 degrees apart so we have no dead end as we do with the first diagram and we could perhaps be more lenient with numbers and travel distances, and yet the situation is clearly less safe than the first diagram.



Exercise caution and sound judgement.

[lyledunn]

Thank you very much guys. Phoenix, superb! Cheers. This is a club room that we are refurbishing and going for an entertainment licence. My confusion arises from the requirement that over 60 in a room requires two means of escape. This room is almost the same as your top sketch Phoenix although with no dead end and with the door on the top wall further towards the alternative exit, so slightly worse. It is clear that for some people in this room there is no alternative MOE. I suppose it would be possible to cram them all in at one end and thus the claim could be made that the whole room compliment would not have an alternative MOE.
By the way Phoenix, I am ultra careful with such things. Having endured the worst of NIs troubles, I was glad to be able to turn my back on and exit and move to an alternative on a number of occasions!

[Phoenix]

I appreciate your caution Lyle, I think it is justified wherever you are in the UK (or the world).

It's not uncommon to have a dead end portion of a room such as you have but in most small and medium places of assembly it would be unusual to find that so many people cram themselves into this dead end that it becomes hazardous, people usually spread themselves out a bit.  Having said that, some venues may have a stage or other attraction at the end of the dead end and this might attract an unusually large number of people into the dead end.  If this happens, do you have to worry if there may be more than 60 in the dead end part of the room? 

I would say no, not automatically.  A dead end part of a large room is not the same as a room with a single exit, people do have more freedom of movement and can travel along one side of the room or the other.  I would recommend not worrying about it unless there was good reason to believe that very many people would go into the dead end area.  Can't put a figure on it as it depends on the width and height of the room but I probably wouldn't even start thinking about it as a potential problem unless the figure was over a hundred.

That's just my opinion, someone else may feel differently.
 

[wee brian]

In most situations you can just look at the MOE and decide if twoi exits are so close together that they should be treated as one.
That's the best approach.

The 45 degree thingy is just an attempt at codifying it for people who refuse to be resonable.

[colin todd]

Ah, so the 45 degree thingy is there for the English fire and rescue service, Brian?

[wee brian]

We dont discriminate - its there for anybody who refuses to just be a bit sensible