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.
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
Problems
with intumescents
Some intumescents have very limited application
because their beneficial properties (and in some circumstances, the applied
intumescent itself) can disappear within days of installation. The culprits are
various environmental influences, such as humidity (even normal indoor
humidity), the UV component of sunlight, and heat generated by normal
operations. Intumescents such as ordinary sodium silicates must be protected by
epoxy or rubber coatings to ensure operability.
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 product’s 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.
Source: Achim Hering http://pubs.acs.org/subscribe/archive/ci/31/i05/html/05hering_new.html
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