The results presented here do not include such possible effects.Īnimal experiments were conducted to determine the toxic effects of the degradation products of rigid cellular PVC, flexible cellular PVC, solid PVC, and PE. For example, certain organo-metals which are used as stabilizers are powerful poisons. When these products are burned with sufficient oxygen, hydrogen chloride, carbon monoxide, and carbon dioxide are produced.īefore this review and analysis began, it became apparent that it is extremely difficult to extract from the general literature information concerning toxic gases given off by PVC or PE formulations intended for specific electrical applications, (i.e., including degradation products of plasticizers, stabilizers, or other materials that are added to the basic polymer). Between 7 degrees Fahrenheit, ethylene, benzene, naphthalene, and other hydrocarbons are produced. Up to about 446 degrees F, hydrogen chloride is given off in a white mist and CO is given off mainly above 482 degrees Fahrenheit. It decomposes in the range of 302 to 572 degrees Fahrenheit flash ignites at 735 degrees Fahrenheit, and self-ignites at 850 degrees Fahrenheit. With the addition of a flame-retardant, PVC's low temperature performance is compromised, (i.e., brittleness is increased, and impact resistance is decreased). PVC is readily ignitable when a plasticizer such as a phlalate is used: however, the flame retardant properties of PVC are retained with a plasticizer such as a phosphate ester. Standard specifications for PVC at 140 degrees Fahrenheit and 167 degrees Fahrenheit appear in ICEA and UL Standards. Test requirements include burning time in a vertical flame test. PVC is used on individual telephone conductors, and also as an extruded layer over the outer PE jacket that covers telephone wire bundles. Flexible PVC insulation is used extensively for wire and cable at power voltages up to 600 volts, and control circuit voltages up to 5 kV, at temperatures up to 221 degrees Fahrenheit. Polyvinyl chloride (PVC) consists of a very long chain of alkenes that are double-bonded with a monomer. If PE burns with poor ventilation, both carbon monoxide (CO) and carbon dioxide (CO2) are produced. The gases include ketones and aldehydes, whose combustion becomes self-sustaining at higher temperatures. It gives off gases starting at about 392 degrees Fahrenheit. PE begins to decompose when exposed to a temperature of 627 to 892 degrees Fahrenheit, and has a self-ignition temperature of 660 degrees Fahrenheit. The high-density variety (HDPE) is similar electrically to low-density PE except for its greater hardness, which increases its tendency to crack. Low-density PE (LDPE) is used for communication and power cable jackets, but its application is limited to temperatures below 170 degrees Fahrenheit because of its low softening temperature. Vulcanized or cross-linked PE has a high molecular weight and low density, and is capable of operating up to about 220 degrees Fahrenheit or higher without melting or dripping. Cross-linking is accomplished by the use of organic peroxides, irradiation, or chemical grafting, followed by exposure to water to induce hydrolysis. Most PE compounds are classified as either low density, high density, or vulcanized (cross-linked). PE is also used in a foamed form in coaxial communications cables. Individual conductors may be covered with PE insulation, and sometimes the PE jacket is covered with a layer of PVC. PE, which is flammable unless a flame retardant such as a halogen compound is added, is used extensively as jacketing over telephone cables. It is composed of chains of alkene groups. PE, first introduced commercially in the early 1950s, is a semi-crystalline polymer. This analysis was based primarily upon reviews of information available in technical literature sources, which provided data on the nature of the emitted gases, various toxicity thresholds, and the results of animal experiments with PE and PVC. In addition to typical criteria related to electrical, mechanical, and environmental exposure characteristics, an analysis and comparison was made of the toxic gases given off by heating or burning of two materials, polyvinyl chloride (PVC) and polyethylene (PE). A large telecommunications company authorized a study to determine which insulation materials to employ on wiring in its central offices.
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