The proof is in the fire
The author looks at the reliability of two international testing standards for passive fire protection products.
Intumescents are substances that swell when exposed to heat. The chemically bound water in intumescents absorbs heat, making them ideal materials for firestopping, fireproofing, and gasketing applications. Some intumescents, however, are susceptible to environmental influences such as humidity, which can reduce or negate their ability to function.
Although somewhat contrary to the true definition, intumescents are categorized as passive fire protection measures because they are used to compartmentalize fire (keep the fire in the location of origin). However, passive does not denote an absence of activity. During the intumescing process, physical activity (swelling) and chemical activity (loss of bound water and char formation) are both taking place.
After I wrote an earlier article in The Construction Specifier (1), I received some strong criticism from manufacturers whose products did not meet the pedigree I suggested. In this article, I provide an update from my previous work and a discussion of the two standardsUnderwriters Laboratories (UL; Northbrook, IL) Standard 1709 (2) and the German Institute for Building Technology (DIBt; Berlin) Guidelines for Intumescent Building Materials (3)currently known to address the most critical issues relating to intumescent longevity, which, incidentally, apply to many other products used in passive fire protection.
A great deal of knowledge exists on the topic of intumescents, and there is no shortage of manufacturers and distributors for intumescents worldwide. The trouble is that many intumescent products do not work after they have been installed and exposed to common environmental conditions. An excellent source of information on the history and modeling efforts can be found on the Web (4).
Types and applications
Low-expansion intumescents tend to have higher strength, partially because they tend to contain less water than the high-expansion intumescents (Figure 3 at right). Depending upon the number of attached waters of hydration, sodium silicates tend to contribute approximately 10% water. Uses of low-expansion intumescents include fire door gaskets, firestops, and closures.
Problems with intumescents
Most vendors of vulnerable intumescents are responsible and clearly state that their products require protection. But not all manufacturers are that responsible and forthcoming. For instance, using commercially available sodium silicates, any moderately skilled entrepreneur conceivably could design a product that will intumesce. The problem is the durability of the product. This is a significant factor, because some regions in Canada, for example, exhibit a wide variety of environmental conditions during a given year. There have been a number of product recalls for faulty firestops in Canada and the United States.
When a car manufacturer recalls a type of car, the owner drives it to the dealer, and the problem is corrected. But it is not quite that simple for passive fire protection products, which are concealed behind the finishes of occupied buildings. I doubt that you will find people digging holes into their drywall or masonry to replace faulty firestops or scraping deficient intumescent fireproofing off structural steel. Building owners are not always well informed of these fireproofing details because they have little to do with the original construction of the building. Thus, in creating the initial design of the formula, the manufacturer should consider the expected environmental exposures of the product and standardized testing and quality control regimes that will assure designers, contractors, and end users about the products reliability.
A product may intumesce in the laboratory, but will it perform the same way a week later in a desert, a jungle, or an arctic environment? At present, environmental exposure tests are not required in North America for most intumescent applications. Structural steel coatings are an exception and are discussed later.
Standards for intumescents
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.
UL test standards
UL1709 methods are intended to fire-test structural steel columns that have been protected with an exterior grade fireproofing material. Because the standard building elements time-versus-temperature curve does not apply to exterior fires involving hydrocarbons, the UL1709 high-intensity or hydrocarbon fire curve is used to measure the much faster heat rises (2). Within the first 5 min of the test, 2000 °F must be reached. The temperature must be maintained for the desired fire-resistance duration, within a prescribed tolerance. The applied intumescent (or any other fire protective material intended to be classified for the same purpose) must keep the 2.4-m-long steel column sample below 1000 °F, on average. None of the eight thermocouples must yield a temperature in excess of 1200 °F.
Running all of the environmental exposure tests takes at least 1.5 years. This duration, along with the cost of testing, is a major factor in the low number of manufacturers vying for this market. Only one vendor that markets an intumescent has qualified its system to all environmental exposure criteria.
DIBt test standards
The DIBt approach contains three sets of tests. Following a set of basic tests that establish sample size, construction, and density, the intumescent qualities of the materials are quantified: how endothermic the product is and the percentage and pressure of its expansion.
The samples are then exposed to a variety of adverse environmental influences. Products are tested only for those environments in which the manufacturer intends them to be marketed. The resulting DIBt approval will clearly spell out what can be used where. The environmental tests include
Finally, the effect of the intumescent on other building materials is tested, specifically poly(vinyl chloride) (PVC) and polyethylene (PE).
Once the samples have been exposed to these adverse environments, the tests of basic characteristics are repeated. The differences in performance, both for foam height and expansion pressure between exposed samples and unexposed samples, are recorded in terms of percentage. All of the testing is performed by governmental laboratories, which are DIBt- accredited.
Within the legal framework of the DIBt standard, all materials must undergo what the Germans call Baustoffzulassung (building material approval), whereby the test results from the DIBt-accredited laboratories are communicated immediately to DIBt, which forwards them to an expert committee (SVA) as a request for approval. Within the report, the laboratory must make a recommendation to the SVA on the eligibility of the product for approval. DIBt indicates the reason for this test and certification regime. Prior to the DIBT standard legislation, Germany had many problems with intumescent materials and application; since the establishment of this standard, there has been one update.
The DIBt method is used as a reliability test to detect any serious problem with an intumescent. Additionally, the DIBt standard contains provisions for adapting unique products and applications. If the procedure has to be altered to determine its efficacy more accurately, changes can be made, but they must be approved by the manufacturer, the DIBt-accredited laboratory, and ultimately the SVA expert committee. The same applies to the testing of environments that are not adequately covered by the means established in the standard. For each change to the procedure, three parties have to agree.
Assessing the intumescent market
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 elses facility, requesting a current DIBt approval and a system qualified to UL1709 is prudent. Beware that for each standard, not every exposure is mandatory.
Achim Hering is an independent consultant on passive fire protection (PO Box 818, Capreol, ON, Canada P0M 1H0; 705-858-4791; firstname.lastname@example.org; www.geocities.com/achim_hering). He is a member of ULC Task Group 21 on firestops and has written several articles on fire protection. He has been involved in passive fire protection since 1981.