2000 Fire Door-Fan Manual updated 2002-05-28 Page 37 of 58
This procedure is much more time consuming than using the flex duct. It consists of
measuring the Lower Leaks by covering the ceiling with plastic. This takes a lot of time but
does give good results particularly in small rooms.
A temporary solid barrier to leakage through a suspended ceiling can be used instead of the
neutral pressure used in the B-2.6.2 "Flex Duct" test. The most commonly used material is 2 or
4 mil polyethylene plastic ("visqueen"), under the ceiling tiles, taped to the T-bar grid and
perimeter walls using 2" paper masking tape.
There are two distinct situations where this technique may be appropriate:
1) If the room does not have slab to slab walls, or
2) If the room is too small for a standard BCLA Flex Duct test (e.g. less than 250 to 500
sq.feet of floor area).
While this approach could be used on a room of any size, it is rarely used on rooms larger than
approximately 1,000 square feet, for the following reasons:
1) The larger the area, the more expensive and disruptive the test becomes.
2) If the room is greater than 500 square feet and has slab to slab walls, a BCLA Flex Duct
test can generally provide acceptable predictions, and
3) If the room is greater than 1,000 square feet, a through smoke pencil inspection per 4-
7.2.3 of the standard can provide sufficient assurance that no significant below ceiling
leakage exists which would cause an unacceptable halon loss. If the smoke pencil
inspection missed some leakage, it is unlikely that this overlooked leakage will be
significant enough to cause the room to fail. It is important to recognise that the larger
the volume, the less sensitive the room will be to leakage. If two rooms are built to the
same relative standard of construction, the smaller one will lose halon faster due to its
less favourable surface to volume ratio.
The plastic under the ceiling technique is the Appendix C procedure.
“CB-2.6.2.9 An alternate method for measuring the below ceiling leaks consists of temporarily
sealing identifiable ceiling level leaks using a flexible membrane, such as polyethylene sheet
and tape, and then measuring the below ceiling leakage solely using door fans drawing from
the lower part of the room. No flex duct is needed. Examples of sealable leaks are
undampered ceiling level supply registers or return grills, or an entire suspended ceiling lower
surface.”