Unsaturated polyester resin is used extensively in the production of composite plastic materials, such as fiberglass products. UPRS are classified by NFPA 30 as Class I flammable liquids, often Class IC, based on their styrene content.

However, because UPR is a viscous liquid with a low vapor pressure and a high density, it has been postulated that UPR stored in drums might behave more like a melted plastic than a non-miscible Class IC liquid when subjected to fire, enabling the use of reduced fire protection system designs as compared to protection schemes ordinarily required by NFPA 30 for Class IC liquids.

A test reported in the April issue of Fire Technology supports this conclusion.

“Our tests demonstrated that palletized storage of UPR in steel drums stacked up to three high can be satisfactorily protected by sprinklers on 10 by 10 spacing and having a water density of 0.45 gpm/sq. ft. when the exposure fire involves spilled resin,” said Joseph Scheffey, of Hughes Associates, a Baltimore fire protection consulting firm.

Scheffey said the 2gpm resin spill used in the test represents a reasonable scenario and a challenging threat to the stored materials, provided that the UPR storage area is protected from liquid spills from other more volatile products. At the 0.45 gpm/sq ft density, all fires were controlled, pile stability was maintained and ceiling temperatures remained well below critical levels throughout the duration of the test.

UPR responds well to sprinkler water discharge, much better than more common Class IB and IC liquids,” Scheffey said.

A concern associated with fire testing of styrene resin was the potential for the material to polymerize when heated and the associated risk of polymerization leading to violent drum failure.

“The tests demonstrated that drums of styrene resin may, in fact, polymerize and become rigid as a result of fire exposure,” Scheffey said.