In North America, the only standard that adequately addresses serious environmental exposures and the longevity of intumescents is UL1709 (Standard for Safety for Rapid Rise Fire Tests of Protection Materials for Structural Steel) (2). Unfortunately, this standard only covers fire testing of structural steel columns against the hydrocarbon time-versus-temperature curve, which essentially restricts its use to fire protection of exterior steel structures in the oil and petrochemical industries (a minority of applications for intumescent products). In fact, testing against UL1709 can deter manufacturers of intumescents, and for good reasons, which are described later.
UL1709 contains a very tough set of tests, as it should, considering the rigorous applications for exterior hydrocarbon fire protection and the enormous risk potential for refineries and chemical plants. This test regime does nothing for interior products because no one has tested common interior passive fire-protection products to UL1709. One reason is that endothermic coatings such as intumescents generally contain large concentrations of epoxy coatings. Consequently, an unacceptably high amount of smoke is generated when the coating is first exposed to fire, and such a large fuel contribution violates building codes across North America.
Although other methods for testing intumescent materials are available, the best and most scientifically sound bench-scale testing is from DIBt. Under the DIBt approval guidelines, building materials are tested for interior or exterior applications. DIBt-approved firestopping, fireproofing, and gasketing products are available in North America; manufacturers include 3M (intumescent firestops) and Nullifire (a thin-film intumescent spray fireproofing product).
Committees from UL and UL of Canada (Toronto) are currently considering mandating the use of a modified version of the DIBt method for bench-scale testing of intumescent products used in firestopping applications. Neither U.S. nor Canadian manufacturers are enthusiastic about an environmental exposure mandate. However, manufacturer due diligence and providing useful and reliable data to the end user are the real issues because it is the costly environmental exposure testing as well as practical performance that causes some intumescents to fail.
Assessing the intumescent market
The largest market for intumescents is the industrial exterior spray fireproofing market. All manner of passive fire protection products compete for this market, including intumescents, other endothermic products, cementitious plasters, fibrous plasters, fibrous wraps, and cast concrete, as well as active fire protection products, such as the type of sprinkler systems used to protect liquefied petroleum gas (LPG) containers.
Let us look at a situation in which problems associated with rival products can be solved by intumescents: petrochemical plants, which contain process pipe bridges (structural steel racks for the purpose of holding up process piping), vessel skirts (round steel sheet structures, which support a vessel above), and spherical or cylindrical LPG containers.
There is a definite demarcation line within petrochemical facilities in terms of the importance given to (and willingness to part with funds to safeguard) pipe bridges and vessel skirts compared with LPG containers. Without vigilant enforcement measures, many above-ground LPG containers remain unprotected and thus subject to fire exposure in case of a flammable hydrocarbon spill. Facility owners who do pay to fireproof their LPG vessels are more likely, if aware of all technical aspects and expenses, to choose an intumescent or other endothermic product, rather than a cementitious or fibrous plaster. There are several reasons for this; one is longevity.
There is considerable variation in reinforcement factors and inherent flexibility between cementitious plaster products used for spray fireproofing (7). Plaster delamination and the corrosion of the steel mesh used to reinforce the plaster have in some cases caused the spray fireproofing to become dislodged and fall off. Common factors known in inorganic chemistry and in the concrete industry contribute to such events. Omitting the exterior waterproofing membrane or the priming layer permits weathering to occur, causing the cement-bound plaster to drop in pH value. This reduces the corrosion protection of the reinforcing mesh, which starts to rust, expand, and thus potentially damage the vulnerable plaster. This effect is especially pronounced in installations near the ocean, where the salt spray accelerates corrosion.
Experience has shown that because of faulty dew-point calculations and insufficient investment in quality materials and installation, fibrous plasters can become soaked with water and then freeze and delaminate. The owner of a petrochemical facility may find that the absolute lowest price is not the best tool for cost effectiveness in the long run.
Intumescent and endothermic products for this application circumvent the problems associated with the cementitious and fibrous plasters, for the most part. There have been cases of misapplication of intumescents (e.g., mixing incorrect proportions of ingredients) leading to the sliding off and total replacement of the product during the initial application. Intumescent coatings have also been known to delaminate; however, these are exceptional cases. One should use caution to choose a competent contractor. Intumescent and endothermic products are supplied in an epoxy paint base, so they are inherently corrosion-inhibiting. They are also much more likely to stretch and move with a sphere as it is being emptied and filled and undergoing weather changes. There can be no water or chloride penetration, and there is no cement to suffer from corrosive effects. Intumescent and endothermic products are significantly more expensive per square meter installed than fibrous and cementitious plasters. In light of the technical aspects, intumescent and endothermic products are worth the extra money, particularly when qualified to the environmental criteria of UL1709 or DIBt.
At present, there is no shortage of vendors for intumescent products, certified or not. If you are a manufacturer of passive fire protection products, it is certainly wise to be up-to-date on DIBt standards. I recommend qualifying your products with this method and obtaining a DIBt approval regardless of where your product may be sold, simply to prove due diligence as a manufacturer. If you are purchasing intumescents for your facility or for resale or you are specifying them for use in someone else’s facility, requesting a current DIBt approval and a system qualified to UL1709 is prudent. Beware that for each standard, not every exposure is mandatory.
Source: Achim Hering http://pubs.acs.org/subscribe/archive/ci/31/i05/html/05hering_new.html
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