Firewall (construction)

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This article is about firewalls used in construction. For the networking term, see firewall (networking).

In construction, a firewall is a passive fire protection item that is required to have a special and unique Fire-resistance rating and is subject to stringent bounding. It is a fire-resistance rated wall assembly that has been constructed in such a manner as to subdivide a building into legal and practical segments in accordance with the locally applicable building code.

Firewalls, protruding THROUGH a roof, with sheet metal flashing on top to preserve the building envelope, separating a building into separate parts. Firewalls are constructed of concrete or concrete blocks, in such a manner as to obtain a fire-resistance rating, as well as to ensure that if there is structural collapse as a result of a fire on one side, this collapse cannot carry over to the other side. Codewise, one may thus reduce the area, as if each segment is a separate building, to avoid the cost of having to install a sprinkler system. Penetrants must be run in such a way as to avoid damage to a firewall. Firestops in firewalls typically have to achieve T-Ratings equivalent to the fire-resistance rating of the wall.

New firewall in Canadian residential construction, about to be finished with sheet metal flashing to preserve the building envelope. The firewall clearly separates the building into two separate residential units, such that fire, smoke and structural damage that occurs as a result of a fire, cannot carry over to the unexposed side.

Firewall, as seen on the inside of a newly constructed townhouse unit in Aurora, Ontario. One can clearly see how the firewall goes past the roofline.

1 Characteristics
2 Cheating in the construction of a firewall
3 Innovation
4 Firewalls outside of building construction
5 See also
6 External links

[edit] Characteristics

Firewalls are constructed in such a way as to achieve a code-determined fire-resistance rating, thus forming part of fire compartments typical for passive fire protection. Germany demands stringent and repeated impact force testing upon "new" systems intended to be qualified for this purpose. Most other countries that have special fire-resistance regimes for firewalls specifically, restrict themselves to mandating the use and arrangement of certain building materials, in order to achieve a minimum, though often unquantified, strength. When constructed as intended, firewalls have proven phenomenally successful.

Firewalls typically extend through the roof and terminate at a code-determined distance above it. They are usually finished off on the top with flashing (sheet metal cap) for protection against the elements.

Firewalls in North America are usually supposed to be made of concrete, including, but not limited to, concrete block (see masonry).

Firewalls are intended to prevent not only fire spread, but also a possible building collapse from one side, to carry over onto its other side.

Firewalls must not be penetrated by certain penetrants in such a way that fire induced penetrant collapse could topple or weaken them.

Firewall through-penetration firestops cannot be de-rated.

Firewall penetrants must usually be non-combustible.

Firewalls may contain closures, such as fire doors and windows capable of achieving a fire protection rating. Such windows may contain wired glass, special tempered glass or sodium silicate fills.

Firewalls are most likely to be required to be fitted with temperature-rated through-penetration firestops, whereby the average temperature must not exceed 140°C and no single point may exceed 180°C above ambient at the start of the test, on the unexposed side.

Firewalls typically carry similar regulations as occupancy separations, apart from the collapse and extensions above the roof features.

[edit] Cheating in the construction of a firewall

Common methods of cheating or cutting corners, where firewalls are concerned, include the substitution with drywall assemblies of equal or lesser fire-resistance ratings, as a novice would not notice such an economically motivated substitution. In North America, this is most likely to occur in residential construction, with buildings below four storeys height.

[edit] Innovation

The most novel, lightweight approach to building firewalls that pass the tough German DIN4102 test as well as North American test regimes including the hose-stream test, include the use of mechanically bonded sheet metal and concrete composite boards ("DuraSteel"). Even though this is a much lighter and fast construction method than the norm, it meets code because it contains a small amount of concrete, albeit cellulose re-inforced, with a mostly sacrificial exposed side, as its hydrates are quickly spent and the fibres are ineffective in holding together the loose powder that is left over from what used to be integral concrete, after even small fire exposures. As a system, however, with a front and a back on each side of the framework, it works very well under any test regime the world over.

[edit] Firewalls outside of building construction

The firewall in an automobile (indicated by the red line)

Firewalls are also regularly found in aircraft and in specially prepared cars for compartmentalisation and competition use. For example, a typical conversion of a production car for rallying will include a metal firewall which seals the fuel tank off from the interior of the vehicle. In the event of an accident, resulting in fuel spillage, the firewall can prevent burning fuel from entering the passenger compartment, where it could cause serious injury or death. In regular stock cars, the firewall separates the engine compartment from the cabin and can, at times, contain fibreglass insulation. Automotive firewalls have to be fitted so that they form a complete seal. Usually this is done by bonding the sheet metal to the bodywork using fibreglass resin.

The term firewall is also commonly used by automotive mechanics to refer to the barrier between the passenger and engine compartments of any vehicle.