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Passive fire protection

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Passive fire protection (PFP) is an integral component of the three components of structural fire protection and fire safety in a building. PFP attempts to contain fires or slow the spread, through use of fire resistant walls, and doors (amongst other examples). All PFP systems, down to the smallest details, are founded upon, and entirely useless without bounding.

Contents

[edit] Structural fire protection

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

  • Active fire protection, which is detection and suppression by automatic or manual means,
  • Passive fire protection, which is compartmentalisation of the fire through the use of walls and floors, and their components, that are designed to withstand fire of a standard duration and intensity, organised into fire compartments, which may consist of one or more rooms or floors, allowing evacuations and protection of critical building components, and
  • Fire protection education, to ensure that occupants and operators of the facility, ship or structure know how to operate and/or maintain applicable systems, how to evacuate or where to seek refuge and how to be sure that they do not inadvertently disable any of the active or passive fire protection systems.

[edit] Main characteristics

Steam, at a 100°C, is considered cold in fire protection. The aim in passive fire protection is typically to maintain the item or the side to be protected at or below either 140°C (for walls, floors and electrical circuits required to have a fire-resistance rating) or ca. 540°C, which is considered the critical temperature for structural steel, above which, it is in jeopardy of losing its strength, leading to collapse. Fire testing involves live fire exposures upwards of 1100°C, depending on the fire-resistance rating and duration one is after. So long as the protective endothermic layer still contains hydrates, the temperature on the unexposed side cannot climb above the boiling point of water. As soon as all the water is spent in fire-resistance testing, the temperature on the unexposed side of fire test specimens, of conventional design, typically increases rapidly.

Common endothermic building materials include concrete and gypsum wallboard. During fire testing of concrete floor slabs, water can be seen to literally boil out of a slab. Gypsum wall board typically loses all its strength during a fire, underlining the need for stringent bounding. The use of endothermic materials is established and proven to be sound engineering practice. Too much water can be a problem, however. Concrete slabs that are too wet, will literally explode in a fire, which is why test laboratories insist on measuring water content of concrete and mortar in fire test specimens, before running any fire tests.

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 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[2] 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.

[edit] Examples

  • fire-resistance rated walls

(construction) (Firewalls not only have a rating, they are also designed to sub-divide buildings such that if collapse occurs on one side, this will not affect the other side. They can also be used to eliminate the need for sprinklers, as a trade-off.

  • fire-resistance rated floors
  • occupancy separations (barriers designated as occupancy separations are intended to segregate parts of buildings, where different uses are on each side; For instance, apartments on one side and stores on the other side of the occupancy separation.
  • closures (fire dampers, fire-resistance rated windows and fire doors. Sometimes firestops are treated in building codes identically to closures. Canada de-rates closures, where, for instance a 2 hour closure is acceptable for use in a 3 hour fire separation, so long as the fire separation is not an occupancy separation or firewall. The lowered rating is then referred to as a fire protection rating, both for firestops, unless they contain plastic pipes and regular closures.)
  • firestops
  • grease ducts (These refer to ducts that lead from commercial cooking equipment such as ranges, deep fryers and double decker and conveyor equipped pizza ovens to grease duct fans. In North America, grease ducts are made of minimum 16 gauge sheet metal, all welded, and certified openings for cleaning, whereby the ducting is either inherently manuf]]</math>actured to have a specific fire-resistance rating, OR it is ordinary 16 gauge ductwork with an exterior layer of purpose-made and certified fireproofing. Either way, North American grease ducts must comply with NFPA96 requirements.)
  • cable coating (application of fire-retardants, which are either endothermic or intumescent, to reduce flamespread and smoke development of combustible cable-jacketing)
  • spray fireproofing (application of intumescent or endothermic paints, or fibrous or cementitious plasters to keep substrates such as structural steel, electrical or mechanical services, valves, liquified petroleum gas (LPG) vessels, vessel skirts, bulkheads or decks below either 140°C for electrical items or ca. 500°C for structural steel elements to maintain operability of the item to be protected)
  • fireproofing cladding (boards used for the same purpose and in the same applications as spray fireproofing) Materials for such cladding include perlite, vermiculite, calcium silicate, gypsum, intumescent epoxy, DuraSteel (cellulose-fibre re-inforced concrete and punched sheet-metal bonded composite panels), MicroTherm
  • enclosures (boxes or wraps made of fireproofing materials, including fire-resistive wraps and tapes to protect speciality valves and other items deemed to require protection against fire and heat - an analogy for this would be a safe)

[edit] 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.

[edit] 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:

  • 1. How many firestops are in your building, where are they located and how do you know which certification listing covers which opening?
  • 2. Show me your copy of the version of the building code that applies to this building and show me your copy of the current fire code.
  • 3. Do you have any spray fireproofing in this building, and if so, what is your method of ensuring that when you install new electrical or mechanical services, that the fireproofing is patched and made good in such a way that the certification listing that was used in the original installation of the spray fireproofing is still bounding your fireproofed items after new cables or piping has been installed?
  • 4. How do you ensure that nobody paints over the certification labels on fire doors and fire door frames?
  • Results: Any verbal deflections by the owner in terms of leaving such details to others, such as the local fire prevention officer or contractors who come and go, can be indicative that no systems are in place to make sure the building is maintained in a manner consistent with the fire code. At times unbeknownst to the owner, fire prevention officers can only comment on what they have actually seen. They're not paid or required to lift ceiling tiles at rated walls and look for missing firestops or damaged spray fireproofing. Typically, only blatant abuses stand out to a fire prevention officer, who may only be given a half hour to inspect a school, for instance. Contractors are typically worried about bringing up permits etc., as the suggestion towards an owner of scrutiny by the Authority Having Jurisdiction (AHJ) can be deemed counterproductive to a contractor's commercial success.

[edit] Common, accredited product certification and testing organisations

  • Europe:

-Testing: Efectis

  • Netherlands:

-Testing: TNO

  • Germany:

-Testing: iBMB/ TU Braunschweig -Testing: BAM Berlin -Testing: MPA Dortmund

-Certification: Deutsches Institut für Bautechnik (DIBt)

[edit] "Old" versus "New"

Generally, one differentiates between "old" and "new" barrier systems. "Old" systems have been tested and verified by governmental authorities including DIBt [3], the British Standards Institute (BSI) and the National Research Council's Institute for Research in Construction [4]. 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 [5] 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.

[edit] 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.

[edit] Bounding examples

  • Breaching a fire barrier:

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.

[edit] See also

[edit] External links

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