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fire-resistance

Fire-resistance rating

A fire-resistance rating typically means the duration for which a passive fire protection system can withstand a standard fire resistance test. This can be quantified simply as a measure of time, or it may entail a host of other criteria, involving other evidence of functionality or fitness for purpose.

The following depict the most commonly used international time/temperature curves:

International fire-resistance ratings

For instance, in Germany, a fire door may have a "T90" designation, which means that the door has documented evidence of its ability to withstand that country's fire door test regime for a duration of 90 minutes.

There are many international variations for nearly countless types of products and systems, some with multiple test requirements.

Canada's Institute for Research in Construction (a part of the National Research Council and publisher of Canada's model building code - NBC) requires a special test regime for firestops for plastic pipe penetrants. Fire endurance tests for this application must be run under 50Pa positive furnace pressure in order to adequately simulate the effect of potential temperature differences between indoor and outdoor temperatures in Canada's winters. Special hoods are applied here to provide suction on the top side of a test assembly in order to reach the 50Pa pressure differential. Afterwards, a 30PSI hose-stream test may be applied.

Some fire doors in the NAFTA area may even open up somewhat during a fire endurance test, although not too far, while a wall or floor assembly proper may not even be allowed an average temperature rise above 140°C or single point increases over 180°C.

Outdoor spray fireproofing methods that must be qualified to the hydrocarbon curve may be required to pass a host of environmental tests before any burn takes place, to minimise the likelihood that ordinary operational environments cannot render a vital system component useless before it ever encounters a fire.

If critical environmental conditions are not satisfied, an assembly may not be eligible for a fire-resistance rating.

Regardless of the complexity of any given test regime that may lead to a rating, the premise is generally product certification and, most importantly listing and approval use and compliance. Testing without certification and installations that cannot be matched with an appropriate certification listing, are not usually recognised by any Authority Having Jurisdiction (AHJ) unless it is in a realm where product certification is optional.

Tests for Fire Resistance of Record Protection Equipment

The following classifications may be attained when testing in accordance with UL 72

Class 125 Rating

This rating is the requirement in data safes and vault structures for protecting digital information on magnetic media or hard drives. Temperatures inside the protected chamber must be held below 125°F (51.7°C) for the time period specified, such as Class 125-2 Hour, with temperatures up to 2,000°F (1,093.3°C) outside the vault. The temperature reading is taken on the inside surfaces of the protective structure. Maintaining the temperature below 125°F. is critical because data is lost above that temperature threshold, even if the media or hard drives appear to be intact.

Class 150 Rating

This is the rating required to protect microfilm, microfiche, and other film-based information storage media. Above 150°F (65.5°C) film is distorted by the heat and information is lost. A Class 150-2 Hour vault must keep the temperature below 150°F. for at least two hours, with temperatures up to 2,000°F. (1,093.3°C) outside the vault.

Class 350 Rating

This rating is the requirement for protecting paper documents. Above 350°F (176.7°C) paper is distorted by the heat and information is lost. A Class 350-4 Hour vault must keep the temperature below 350°F. for at least four hours, with temperatures up to 2,000°F. (1,093.3°C) outside the vault.

Different time/temperature curves

Typically, most countries use the building elements curve, which is nearly identical in most countries as that is what results by burning wood. The building elements curve is characterised jointly by, including, but not limited to, DIN4102, BS476, ASTM E119, ULC-S101, etc. For exterior systems used in the petrochemical industry, the hydrocarbon curve is used. The only exposure beyond this, apart from the more recent tunnel curves shown above, would be the British "jetfire" exposure, which is not commonly used.

Big differences between different countries in terms of the use of the curves include the use of pipes, which shield the furnace thermocouples inside of NAFTA testing laboratories. This slows down the response time and results in a somewhat more conservative test regime in North America. On the other hand, the ISO based European curves run somewhat hotter for most of the test. North America also selectively uses a hose-stream test between 30 and 45PSI, to simulate real-world impacts and damages that may not be simulated in a laboratory. The US Navy even insists on a 90PSI hose-stream test for some of its assemblies, which may simulate the pressure available to firefighters in fighting a fire, but which has little to do with countermeasures against damaging effects of manual fire suppression. The hose-stream is simply intended to add a level of toughness to matters because without this, some fairly flimsy systems can pass a test, thus receive a rating and thus be permissible by a building code but be so weak that ordinary building use may damage a thus qualified system before it encounters a fire. See firestop.org treatise on the hose stream test

Germany's DIN4102 also includes a significant impact test for a potential firewall (construction), which is, however, applied from the wrong side: the cold side. Applying the impact from the cold side is more practical to do in a lab setting, however, potential impacts should come from the exposed side, not the unexposed side. Still, for the person designing, building and paying for the test, the fire resistance itself may be rather uneventful unless major problems appear. The burn itself is the long duration, up to 4 hours, but the hose stream test only lasts a few minutes, with large damage potential due to the sudden thermal and kinetic impacts, as the fire was upwards of 1,100°C (see curves above), whereas the sudden hose-stream test is as cold as the domestic water fed to the fire hose used in the test, which might be 10-20°C. This combined impact explains the debris that can be seen coming from test specimens during the hose stream test, as seen herein.

Because of the large differences in test regimes all over the world, even for identical products and systems, organisations that intend to market their products internationally are often required to run many tests in many countries. Even where test regimes are identical, countries are often reluctant to accept the test results and particularly the certification methods of other countries.

During a fire in a tunnel, as well as in the petrochemical industry, temperatures exceed those of ordinary building (cellulosic) fires. This is because the fuel for the fire is hydrocarbons, which burn hotter (compare hydrocarbon curve above to ASTM E119 curve), faster and typically run out of fuel faster as well, compared against timber. The added complication with tunnels is that the environment inside a "tube" is best described as a "microclimate". The heat cannot escape as well as it can in a burning refinery, which is in the open. Instead, the fire is confined to a narrow tube, where pressure and heat build up and spread rapidly, with little room for escape and little chance of compartmentalization. This scenario was amply tested and quantified, particularly during the "Eureka Project", run by Technische Universität Braunschweig's iBMB, Dr. Ekkehard Richter, which has profoundly affected tunnel regulations in the Nations that took part in the project. The Netherlands, through Rijkswaterstaat in particular, mandated an extremely tough standard, the curve of which is shown in the gallery above.

Example of a test leading to a fire-resistance rating

The following is a series of pictures depicting a typical fire test, in this case for a firestop, which led to an active fire-resistance rating, backed up by active product certification. A copy of the resulting certification listing can be seen under the certification listing article.

Picture 1

Construction of a test sample, consisting of a mock-up concrete floor frame, complete with penetrants. The concrete frame measures approximately 5’ x 9’ x 4“ (ca. 1.5m x 2.3m x 10cm). It has a large hole in the centre with many mechanical and electrical services traversing. The penetrants extend 1’ (30cm) into the furnace and 3’ (91cm) on the unexposed side. A firestop mortar is being applied here. Notice the intumescent wrap strip surrounding the fibreglass pipe insulation. When the fire starts, this embedded intumescent will swell to take up the place of the melting insulation. The test was conducted in accordance with the Canadian firestop test method ULC S-115 in Scarborough, Ontario.

Picture 2

The completed test sample is being lifted by crane to the test furnace for the fire resistance test. By contrast, European furnaces can typically allow up to a 1m penetrant depth to reach into the furnaces. North American panel furnaces are not deep enough to accommodate this more realistic exposure.

Picture 3

After the completed test sample has been seated on a ceramic fibre gasket on the top of the furnace, gas is let in through perforated pipes at the bottom of the furnace. The ULC technician is now igniting the gas on each pipe to start the test. Thermocouples are located inside the furnace to make sure the fire resistance test is run in accordance with the prescribed time/temperature curve. Further thermocouples are located on the firestop, 1” or 25mm away from each penetrant and on each penetrant, 1” or 25mm up from the surface of the firestop. The length of time the test is run and/or however long it takes for fire to penetrate the firestop determines the F-Rating. The length of time required for a penetrant and/or the sample on average to exceed an average heat rise above ambient at the start of the test to exceed 140°C or 180°C at any single location – this determines the duration for the FT Rating (Fire and Temperature). If the hose-stream test is passed afterwards, the rating can then be expressed as an FTH Rating (Fire, Temperature and Hose-stream). The lowest of the three determines the overall rating, though it is possible to have a wide variety of T results, which can vary depending upn how well each such penetrant conducts heat.

Picture 4

At the conclusion of the fire resistance test, the test sample is lifted off the furnace and readied for a hose-stream test, which is NOT intended to simulate the effects of firefighting. Instead, it is to add a measure of reality of possible impacts, thermal shock and generally the brutal environment of a real fire, which is hard to simulate in pristine laboratory conditions. See this With combustible penetrants like cables or combustible firestops like silicone foam, it is not entirely unlikely even after two hours of fire to see residual flaming on the exposed side. For an example, see this picture This was proven during a highly publicised fire test at ULC that encased the silicone foam with noncombustible sheathing in an attempt to justify in-situ installations in US and Canadian nuclear reactor facilities, as per submissions provided to Select Committee on Ontario Hydro Nuclear Affairs by Pickering, Ontario Regional Councillor Maurice Brenner

Picture 5

The duration and pressure of the hose-stream test are a direct function of the length of the test and the size of the test sample. The most typical test pressure is 30PSI, though 45PSI may also be used for fire tests of 4 hours duration or longer.

Picture 6

The test can be considered passed if no fire, water and no excessive heat traversed the sample or penetrants. All results are tabulated and form part of the rating designations, which can be quite complex in the case of busy firestop tests such as this. For instance, an uninsulated copper pipe may have only a 5 minute T Rating, whereas that same pipe insulated with 2” or 50mm of rockwool may achieve a 2 hour T-Rating. Product certification listings resulting from such successful testing can be used to obtain the approval and acceptance of installed configurations on the part of the Authority Having Jurisdiction on construction sites. Listings are considered public knowledge, whereas the test report itself would be a proprietary item.

Picture 7

Observations from both sides of the test assembly continue on the next day, once the sample has cooled down sufficiently. It is also customary to destroy the test sample, for two reasons: to learn from the effects of the test on the inside of the sample Research and development, as well as for a test laboratory which would issue a certification listing on the basis of the test to ensure that the listing reflects accurately what was installed inside the test assembly, in case and changes occurred that were not previously documented.

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