Test

Strength vs. temperature of steel and plastics (Courtesy of Plastics FALLO)

-100 0 100 200 300 400 500 600 700 800 9001000 ■ V1500

TEMPERATURE, F'

-100 0 100 200 300 400 500 600 700 800 9001000 ■ V1500

TEMPERATURE, F'

in fact often correlate directly with those of another and may bear little relationship to actual fires. There are tests that are intended for screening purposes during R&D. Tests such as large-scale product tests, are designed to nearly approximate actual fires.

Terms used that relate to fires includc self-extinguishing, nonburning, flame spread, and toxicity. They are to be understood in the context of the specific tests with which they are used. Some materials may burn quite slowly but may propagate a flame rapidly over their surfaces. Thin wood paneling will burn readily, yet a heavy timber post will sustain a fire on its surface until it is charred, then smolder at a remarkably slow rate of burning. Bituminous materials may spread a fire by softening and running down a wall. Steel of course does not burn, but as reviewed, is catastrophically weakened by the elevated temperatures of a fire. PVC, silicone and fluorine does not burn, but it softens at relatively low temperatures. Other plastics may not burn readily but still emit copious amounts of smoke. And some flammable plastics, such as polyurethane, may be made flame retardant (FR) by incorporating in them additives such as antimony oxide.

In applying fire safety in a design requires information on where and how the product is to be used. According to those requirements the principles of good design for fire safety can be applied as they relate to plastics as to other materials. It is often helpful to select plastic materials for specific applications by first evaluating the flammability of the plastics in laboratory tests if the data is not available. These tests, often used for specifying materials, fall into the category either of small- scale or large-scale tests. Of course, as in evaluating any properties, having prior knowledge or obtaining reliable data applicable to fire or other requirements is the ideal situation.

There are different products that have specific fire tests. As an example for appliance safety the Underwriters Laboratory (UL) have published more than four hundred safety standards to assess the hazards associated widi manufacturing appliances. These standards represent basic design requirements for various categories of products covered by the organization. For example, under UL's Component Plastics Program a material is tested under standardized, uniform conditions to provide preliminary information as to a material's strong and potentially weak characteristics.

The UL's plastics program is divided into two phases. The first develops information on a material's long- and short-term properties. The second phase uses this data to screen out and indicate a material's strong and weak characteristics. For example, manufacturers and safety engineers can analyze the possible hazardous effects of potentially weak characteristics, using UL standard 746°C.

It is the general consensus within the worldwide "fire community" that the only proper way to evaluate the fire safety of products is to conduct full-scale tests or complete fire-risk assessments. Most of these tests were extracted from procedures developed by the American Society for Testing and Materials (ASTM) and the International Electrotechnical Commission (IEC). Because they are time tested, they provide generally accepted methods to evaluate a given property. Where there were no universally accepted methods the UL developed its own.

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