Firestop pillow
From Wikipedia, the free encyclopedia
Firestop pillows are passive fire protection items, subject to stringent bounding, used for firestopping holes in wall or floor assemblies required to have a fire-resistance rating.
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[edit] General use
Where there are openings that require frequent access for reasons such as cable changes, the need to reseal them effectively through simple means has driven the development of the firestop pillow. The notion of re-enterability (a buzzword in the firestop field), the primary feature of firestop pillows, characterises an unquantified and undocumented measure for the ease with which changes can be made to a firestop.
[edit] Technical issues and common misconceptions
There are three types of firestop pillows:
- rockwool batts with intumescent resin inside plastic bags
- vermiculite with intumescent graphite inside of fibreglass bags
- intumescent foam rubber
A hose-stream test, which is mandatory for firestops in the US and well-liked in Canada, qualifies the openings and firestop pillow combinations as effective against the force of a 30 psi water stream. To accommodate larger openings that can allow the pillows to become dislodged, wire mesh is sometimes used although one vendor uses heavy-duty grids and claims it is "burglar-proof". Installing firestop pillows correctly is not as easy as one might think or be lead by the literature to believe. One may need to achieve a certain compression rate, which needs to be quantified for each hole. This would entail an accurate calculation of the area of the opening less the area covered by the penetrating items. Then one must factor in the required compression ratio of the pillows to calculate just how many need to be installed. Without this information, there is no evidence of bounding. If the certification listing that is bounding the opening does not mention the compression ratio, using pillows is inadvisable. It stands to reason that one must compress the pillows adequately in order to pass the test.
Another aspect of bounding is ensuring pillow coverage between cables. If there is no requirement to install the pillows between the cables, this means that it is imperative that the cables used in the installation match those used for testing, which is unlikely under field conditions. It is also a physical impossibility to prevent smoke migration through the interior of a cable bundle, if the bundle is not opened up and sealed on the inside during the installation of any firestop, regardless of whether the firestop is intumescent or not. No intumescent can be expected to spread between multiple layers of cables, from the outside towards the inside. If viewed in plan view, each cable represents a circle. In a bundle, as cables are in contact, there are necessarily empty spaces between cables, which invite smoke and heat transfer. An intumescent firestop may reach somewhat into the first layer of cables but to push beyond this takes more force than can be reasonably expected to be generated through an intumescing process. Theoretically, after one calculates the compression rate to determine just how many pillows should be installed, then one has to install the mesh, or grating, or grid, then the pillows. When one uses the mesh, mechanical fasteners are required, including, anchors, bolts etc. In many cases, the effort required negates the touted and perceived benefits of fast installation and "re-enterability" that is typically purported to be provided by this technology.
The last type of pillow comes from an entrepreneur from Cologne, Germany who has been private-labelled it for other companies all over the world. Its basic material is Bayer Fomox intumescent foam, which can be extruded into various shapes. For countries that use a hose-stream test, the Fomox is re-enforced with intumescent graphite, whereas for those who don't use a hose-stream, this ingredient is omitted. The product is basically intumescent foam rubber.
[edit] Repairs/maintenance
As with all other firestops, bounding drives everything. Pillows may present an opportunity for vandalism if not properly secured.
[edit] Smokeproofing
Field installations of firestop pillows do not offer any realistic resistance to air pressure differences or smoke penetration.
[edit] Technical concepts
In the case of batt-based firestop pillows with intumescent resin: the intumescent contains hydrates, or chemically bound water. The fire hits the pillow. On the fire side, the plastic bag burns off. The intumescent gets activated and releases the water in the form of vapour or steam. The steam rises and hits the plastic bag interior on the unexposed side. That's where it condenses back to water, which runs back down to cool matters below and thus the cycle keeps going. This really happens. You can see the droplets during the test and the pillows tend to be cool to the touch on the unexposed side. This concept, however, does not negate the installation and bounding issues, which tend to defeat pillows on a regular basis. The advantage with the batt-based pillows is that proper compression can hold them in, simply through friction - until the "bounce-back" effect has been reduced through frequent use.
For the fabric bag based pillows, the vermiculite, the fabric bag and the graphite are noncombustible, which is beneficial. The graphite expands but forms no bond with anything around it, unlike the resin-based instumescents. There is also no significant release of chemically bound water. Usually the bags are not entirely filled and are, thus, quite floppy, requiring strung mesh or grid installations just to stay in during normal operations.
The Fomox-based pillows simply intumesce as they are supposed to do and work quite well, except that proper installations and compression ratios are still not easy to quantify and guarantee.
Older versions of firestop pillows have no intumescent contents at all, which makes it difficult to pass a hose-stream test. They have not been in use for many years.
