Ask Dr. Dave

Ask Dr. Dave

In his July 2008 column, Dr. Dave discusses fire-retardant adhesives and the necessary approvals for sealants used on pipes carrying potable water.

Question: I typically deal with both epoxy and acrylic systems. Do you have any tips for making my adhesives fire retardant?

Answer: Fire retardants have historically been based on either inorganic materials or halogenated organic compounds. The entire subject of fire retardancy has been hotly debated in recent years because of the negative environmental aspects concerned with certain brominated materials. Phosphate and phosphonate compounds are typical alternative flame-retardants that do not make use of halogens. In adhesives, the choice of fire retardants is dependent on the type of system you are using. In a typical filled epoxy system, you can almost certainly use a combination of a solid inorganic fire retardant such as aluminum trihydate or magnesium hydroxide, perhaps supplemented by an organic one. However, if you have an unfilled acrylic system, particularly one with low viscosity, the choice of materials is much more limited. In this case, you might consider the handful of brominated or phosphorous-containing monomers that can be co-polymerized into the adhesive. There are several suppliers who specialize in fire retardants, and they can advise you on both product performance and safety aspects.

Question: What sort of approvals do I need for sealants used on pipes carrying potable water?

Answer: Sealants for contact with drinking water must be certified to a national standard called ANSI/NSF Standard 61. Several organizations are accredited by ANSI (American National Standards Institute) to test and certify this sort of product. The testing involves exposing the cured sealant to standardized test waters at specified temperatures and times and analyzing the extraction water for target contaminants. Results of this laboratory testing are then “normalized” to estimate their concentrations in specific pipe sizes or tanks, and a material will normally be certified for specific sizes and for specific water temperature use, defined as commercial hot water (180°F), “domestic” hot water (140°F), or cold water. The entire process of obtaining this certification can take many months, and I would advise reading the standard carefully before initiating testing so that you know the target contaminants and can determine whether or not your sealant has a good chance of passing the extraction testing.


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