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By Alex Wilson

In addition to toxicity concerns, the chemicals emitted by FEP (and to a lesser extent by PVC) during a fire are highly corrosive. An article by Stephen Saunders, “Cabling: What You Don’t Know Can Kill You” (posted at www.wireville.com), suggests that it is the corrosivity of halogen-insulated wiring that may ultimately shift us away from halogen-based wire insulation and jacketing. Frank Bisbee, a data cable consultant and editor of www.wireville.com, suggests that how good or bad a particular type of cabling looks—relative to toxicity and potential for corrosive by-products to cause damage to electronic equipment—is highly dependent on how the tests are performed. If humidity during testing is very low, for example, there won’t be enough water vapor to convert hydrogen fluoride into hydrofluoric acid, or hydrogen chloride into hydrochloric acid, and acid corrosion will be less of a problem. Depending on the amount of oxygen present during a fire, the resultant emissions will vary tremendously, he says.

Making wires workable

To make insulated cables easy to manufacture and safe for buildings, three additives—plasticizers, stabilizers, and flame retardants—are typically added to insulation and jacket materials.

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Plasticizers are usually added to PVC to make it flexible enough to be used to insulate wires. The most common plasticizers used in PVC are phthalate compounds, which have come under scrutiny because their chemical composition mimics natural hormones in humans and other animals, causing reproductive problems and birth defects. Unlike PVC, polyolefins used for wire insulation do not require the use of plasticizers.

Stabilizers are added to some plastics to increase resistance to heat, sunlight, moisture, and other stressors. The most common stabilizers used in insulation and jacketing are lead compounds, which can constitute 2 to 5 percent of the total weight of the material. PVC is the only widely used resin for which lead stabilizers are needed. Other stabilizers beginning to appear on the market include salt-metal blends, such as barium-zinc and calcium-zinc; organotin compounds; and metal-free organic compounds. Cable manufacturer Mohawk/CDT is one of the companies shifting to lead-free PVC; according to Michael Rubera, Mohawk’s director of technical support, the company primarily uses polyolefin insulation and lead-free PVC jacketing on its non-plenum-rated data cables.

Flame retardants are added to plastics to slow the spread of a fire, reduce the amount of heat and smoke emitted during a fire, and cause a fire to self-extinguish. They operate by different means. Some retardants reduce the fuel content of the material, for example; others raise the decomposition temperature of the polymer by more tightly bonding the molecules; still others emit water at high temperatures.