Thanks Guys,
What table 13 says is:
"Table 13 Door widths when minimum fire protection measures are provided
Risk profile Minimum door width per person (mm)
A1 3.3
A2 3.6
A3 4.6
A4 Not applicable
B1 3.6
B2 4.1
B3 6.0
etc..."
What note 4 on page 83 of 9999 says is:
"NOTE 4 The total number of persons that two or more available exits can accommodate is found by adding the maximum number of persons for each exit width. For example, three exits each 850 mm wide, in a building with a B2 risk profile, will accommodate 386 persons. This is calculated by:
• 850 divided by 4.4 (from Table 13) = 193;
• discount one exit;
• 2 × 193 = 386 persons [not the 579 persons who could be accommodated through a single exit 2 550 mm (i.e. 3 × 850 mm)
wide]."
Now, everyone can see that B2 in the table says 4.1mm and the note says 4.4mm
Ok, so this is a typo, but how is it corrected? Like this:
"two 100% official typos for you to amend:
page 83 17.6.1 Note 4
850 should be divided by 4.6 rather than 4.4...."
Where does 4.6mm come from?!
Ok, here's another thing. That whole note 4 (quoted above) is a dog's dinner anyway. It is a redundant note that was put in for spurious reasons:
Many years ago designers had a habit of adding together all the individual exit widths to produce one aggregated width, they then subtracted the largest exit and then divided the result by 5mm to come up with an occupancy figure. For reasons that are a little complicated to explain this method gives correct results provided that all exits are at least 1100mm wide. If any exits are below this width then what is being done is that the 5mm per person is being applied to doors below 1100mm which (according to ADB) should not be done.
In an effort to stop this happening ADB introduced paragraph 3.22:
"3.22 The total number of persons which two or more available exits (after discounting) can accommodate is found by adding the maximum number of persons that can be accommodated by each exit width. For example, 3 exits each 850mm wide will accommodate 3 x 110 = 330 persons (not the 510 persons accommodated by a single exit 2550mm wide)."
That makes sense within the context of ADB's table 4. But in 9999, where "x"mm per person is applied down to the minimum exit width possible, this statement is meaningless and redundant. In effect, all note 4 says is to repeat that the largest exit should be discounted. In light of the confusion it generates, I would recommend ignoring note 4.
Stu
