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Passive fire protection

Encyclopedia : P : PA : PAS : Passive fire protection

Fire-resistance rated wall assembly with fire door, cable tray penetration and intumescent [link] cable coating.
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Fire-resistance rated wall assembly with fire door, cable tray penetration and intumescent [link] cable coating.

Passive fire protection (PFP) is an integral component of the three components of structural fire protection and fire safety in a building. All PFP systems, down to the smallest details, are founded upon, and entirely useless without bounding.

Contents

Structural fire protection

Fire protection in a building, offshore facility or a ship, is a system with equally important components, including:

Main characteristics

Passive Fire Protection measures are intended to contain a fire in the fire compartment of origin, thus limiting the spread of fire, excessive heat and corrosive, re-ignitable and fatal flue gases for a limited period of time, as determined by testing, which must bound (see bounding) the installed configuration in all respects in order to comply with the law, which is typically the local building code and the fire code.

Contrary to active fire protection measures, passive fire protection means do not typically require electric or electronic activation or a degree of motion. Exceptions to that particular rule of thumb are fire dampers (fire-resistive closures within air ducts, excluding grease ducts) and fire door closers, which must move, open and shut in order to work, as well as all intumescent[link] products, which swell, thus move, in order to function.

PFP in a building can be described as a group of systems within systems. An installed firestop, for instance, is a system that is based upon a product certification listing. It forms part of a fire-resistance rated wall or floor and this wall or floor forms part of a fire compartment, which forms an integral part of the overall fire safety plan of the building, which, as a whole, can also be seen as a system.

Examples

Regulations

The number one requirement in North America and Germany for code compliance of all PFP is bounding.

Apart from bounding, the other common thread is that PFP is an integral component of the two main aims of building and fire codes, which is structural integrity and fire safety, all with the main aim of life safety, whereas property protection and continuity of operations tend to be secondary considerations in codes. Exceptions include nuclear facilities and marine applications, as evacuation may be more complex or indeed impossible. Nuclear facilities, both buildings and ships also have an interest in ensuring that the nuclear reactor does not experience a meltdown. In this case, fixing the reactor may be more important than evacuation for key safety personnel.

The fundamental basis of the testing that underlies the eventual bounding is the following:

Each of these test procedures have very similar fire endurance regimes and heat transfer limitations. Differences include the hose-stream tests, which are unique to Canada and the United States, whereas Germany includes a very rigorous impact test during the fire for firewalls. Germany has also taken heat induced expansion and collapse of ferrous cable trays into account for firestops. That, is unique to Germany and favours firestop mortars, which tend to hold the penetrating cable tray in place, whereas "softseals", typically made of rockwool and elastomeric toppings have been demonstrated in testing to be torn open and rendered inoperable when the cable tray expands, pushes in and then suffers tray collapse. Spin-offs from these basic tests cover closures, firestops and more. Furnace operations, thermocoupling and reporting requirements remain uniform within each country.

In exterior applications for the offshore and the petroleum sectors, the fire endurance testing uses a higher temperature and faster heat rise, whereas in interior applications, such as office buildings, factories and residential, the fire endurance is based upon experiences gained from burning wood. This, incidentally, is an item of dispute at times, as more plastic is being used all the time in construction, leading some to believe that the old wood-based curve, which is being used all over the world, with only minor variations, may be inadequate. The interior fire time/temperature curve is referred to as "ETK" (Einheitstemperaturkurve = Standard time/temperature curve) or the "building elements" curve, whereas the high temperature variety is called the hydrocarbon curve as it is based on burning oil and gas products, which burn hotter and faster. The most severe, and most rarely used, of all fire exposure tests is the British "jetfire" test, which has been used to some extent in the UK but is not typically found in common regulations.

Typically, during the construction of buildings, fire protective systems must conform to the requirements of building code that was in effect on the day that the building permit was applied for. Enforcement for compliance with building codes is typically the responsibility of municipal building departments. Once construction is complete, the building must maintain its design basis by remaining in compliance with the current fire code, which is enforced by the fire prevention officers of the municipal fire department. An up to date fire protection plan, containing a complete inventory and maintenance details of all fire protection components, including firestops, fireproofing, fire sprinklers, fire detectors, fire alarm systems, fire extinguishers, etc. form the legal defence basis of compliance with applicable laws and regulations.

Generally, all changes to fire protection systems or items affecting the structural or fire-integrity or use (occupancy) of a building is subject to regulatory scrutiny, meaning that a contemplated change to a facility requires a building permit, or, if the change is very minor indeed, a review by the local fire prevention officer. This has a variety of reasons. For one thing, every municipality aims to have accurate building records for emergencies, be they for fires, other disasters or law enforcement. Modern fire departments at times have building plans electronically transmitted into fire trucks which are enroute to the target building. Similarly, law enforcement can "wargame" and better execute rescue operations with accurate building records. Building permit fees cover expenses incurred in the review of contemplated changes. Such reviews by the Authority Having Jurisdiction (AHJ) also help to prevent potential problems that may not be apparent to a building owner or contractors. Large and very common deficiencies in existing buildings include the disabling of fire door closers through propping the doors open and running rugs through them and perforating fire-resistance rated walls and floors without proper firestopping.

Checking for proper PFP care by a building owner

An excellent test of proper stewardship of the PFP systems in a building on the part of the owner includes posing the following questions:

Common, accredited product certification and testing organisations

-Testing: iBMB/ TU Braunschweig [link]

-Certification: Deutsches Institut für Bautechnik (DIBt) [link]

\"Old\" versus \"New\"

Generally, one differentiates between "old" and "new" barrier systems. "Old" systems have been tested and verified by governmental authorities including DIBt [link], the British Standards Institute (BSI) and the National Research Council's Institute for Research in Construction [link]. These organisations each publish in codes and standards, wall and floor assemby details that can be used with generic, standardised components, to achieve quantified fire-resistance ratings. Architects routinely refer to these details in drawings to enable contractors to build passive fire protection barriers of certain ratings. The "old" systems are sometimes added to, through testing performed in governmental laboratories such as those maintained by Canada's Institute for Research in Construction, which then publishes the results in Canada's National Building Code (NBC). Germany [link] and the UK, by comparison, publish their "old" systems in respective standards, DIN4102 (Germany) and BS476 (United Kingdom). "New" systems are typically based on certification listings, which must be installed in a "bounded" manner (see bounding), whereby the installed configuration must, in all respects, comply with the tolerances set out in the certification listing that covers it. The United Kingdom is an exception to this rule, whereby certification, although not testing, is optional.

Countries where certification is optional

Fire tests in the UK are reported in the form of test results, but contrary to North America and Germany, building authorities do not require written proof that the materials that have been installed on site are actually identical to the materials and products that were used in the test. The test report is also often interpreted by engineers, as the test results are not communicated in the form of uniformly structured listings. In other words, in the UK, and other countries which do not insist on certification, the proof that the manufacturer has not substituted other materials apart from those used in the original testing, is based on trust in the ethics, or, possibly, the culpability of the manufacturer. While in North America and in Germany bounding is the key to the success and legal defencibility of passive fire protection barriers, alternate quality control certifications of specific installation companies and their work is available, though not a legislative or regulatory requirement. Still, the question of how one can be sure, apart from faith in the vendor, that what was tested is identical to that which has been bought and installed is a matter of personal judgment.

Bounding examples

If a perfectly rated and well installed fire-resistance rated wall assembly has been built, but now a hole has been drilled through this wall and a cable has been run through the opening, the fire-resistance rating has just been lost. What was before perhaps a two-hour barrier, is now a zero minute barrier because fire and smoke and heat can go right through the hole and spread along the plastic cable jacketing into other fire compartments. If the opening is two square feet in size but a firestop that now fills the hole has only been tested and certified for a one square foot opening, then the rating of the entire wall is still zero because no proof exists that the firestop will work when used beyond the certification listing limitations.

An apartment is vacated and is suddenly used to store oil-based paint cans and mineral spirits. In this case, as in all changes of use or changes of occupancy (from people with their belongings to paint and thinner) the whole building must be re-evaluated. The fire loading would have changed so drastically, that instead of two hour walls and floors, perhaps three hour walls and floors are now needed to segregate this space. Additionally, extra suppression and detection systems are most likely needed, along with a building permit. In this example, the original bounding is almost irrelevant, as complete upgrades with new systems may be required, which may be both PFP and AFP, in nature.

See also

 

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