BS 9999 definitions

[stugood]

Any views or opinions on the following would be appreciated :BS 9999 (2008) Page 16 para :3.77, it states, "a mezzanine floor is a floor that is ancillary to the main use of the building,does not exceed 20% of the floor area of the lower floor or 500 square metres,whichever is less, is compartmented from the lower storey and has M.O.E. that is independent of the lower floor."

How can it be compartmented if it is a mezz floor?......help please

[kurnal]

I suppose it only matters depending on the context in which it is ussed, mezzanine is not defined in BS4422 or the approved document B. I did have a quick look in 9999 to see if I could find any further reference to mezzanines within the document without finding anything. Have you seen  anything further?

It would be relevant in terms of relaxations to the fire resistance of elements of structure - eg for small raised storage areas as per ADB, but other than that have drawn a blank at present.

 

[Tom Sutton]

Could it be the use of specific words. It says, is compartmented from the lower storey not floor and could be interpreted as the mezzanine and lower floor compartmented from the storey below.  

[Phoenix]

Tom, I think you're being very generous in looking for a rational explanation for what is actually a little irrational. 

Stu, the document gives this definition then does very little with it (just a bit of general guidance in 14.1 which I shall come back to in a minute) for the rest of the document.  The document can define mezzanines however they like (perhaps as double ended black umbrellas with yellow spots!) but if it subsequently makes no reference to them then the definition is a waste of time.

I would pay no further attention to this definition and certainly do not adopt it when consulting other guidance documents.

With reference to your closing question, Stu: in 14.1 the document says, "there is always a risk of rapid fire growth resulting in flames spreading beyond the edge of the mezzanine or gallery floor and hence posing a threat to life safety.... Additional safeguards might therefore be necessary to compensate for the increased level of hazard if a fire occurs below the mezzanine or gallery."  I am inclined to agree with you in wondering how these flames are going to spread round the edge of the mezzanine when there is a compartment wall in the way.

Well done for spotting this anomoly but don't pat yourself on the back too hard as there are dozens of these to trip over in 9999 (although I do, in principle, like the document).

Stu too

 

[Tom Sutton]

Stu 2 why do you think they used the word storey instead of floor but as you have said if it makes no reference to them, then the definition is a waste of time.

[Phoenix]

I don't know Tom.  Maybe you're right.  But it seems to me to be a subtle distinction and if they wanted to differentiate between floors and storeys I would have expected to see these defined so that there could be no ambiguity.

Stu

[Tom Sutton]

I would have expected to see these defined so that there could be no ambiguity.

I agree, also to add to the confusion mezzanine floors can be open like a balcony or enclosed like offices I have seen located on the shop floor, usually with storage underneath. I would also describe it as an intermediate floor which could make it more understandable.

[nearlythere]

"Mezzanine" is just a descriptive word and has little meaning in the context of MOE. As it has it's own MOE it does not matter what size it is unless it requires an alternative due to the number of persons it is designed for.
What would it be called if it was 20+%? - A room with an open stairway to a lower floor and an alternative MOE, just like a mezzanine.

[Tom Sutton]

Mezzanine appears in BS 9999 (2008) Page 16 para :3.77 comes under terms and definitions and appears not to be well written considering the comments above. However as a definition it is what you should use when the word mezzanine appears in the BS 9999 fortunately it only appears in 14 Designing means of escape para 14.1.(d). We will have to wait for the revision maybe?