"The availability of commercial flame arresters listed by nationally recognized testing laboratories has frequently led to the installation of these devices in piping systems. The installation conditions may be far different from those under which the flame arrester was tested and listed by the testing laboratory. A flame arrester is limited in its effectiveness due to its design conditions@ and a ""listed"" arrester should not be installed in a piping system unless it has been tested under conditions identical to the specific application. Listed arresters are normally tested under nonflowing conditions and with a limited length of piping downstream of the arrester. Flames propagating through a closed piping system continuously accelerate and can reach velocities much higher than those at which the arrester was tested. As a result@ listed flame arresters may not be effective when incorrectly applied in a piping system. This publication is intendedto alert industry to the limitations of arresters due to the highly variable conditions surrounding their application."