HREE's are used in such small quantities that extraction is often impractical to extract them is no economical or environmentally sound. Often they are used as catalysts and are consumed in the manufacturing process etc, or the risk of mixing the compounds and creating a volatile substance is also a risk.
Safety Concerns
“The fire is not the only safety problem,” says John Michlovic, manager of technical services and marketing for H.H. Robertson Floor Systems. The plastics used in the insulation and jacketing may also release toxic gasses and smoke in a fire scenario. The fire doesn't necessarily ignite the cabling jackets immediately, but the heat can cause it to release clear or white toxic gases that are highly dangerous. These gases can be blind you or shutdown your respiratory system. Incapacitation of the building occupants is a real problem that is not addressed by the testing or the NEC.
"Plenum rated cabling may start burning in 35 to 40 seconds to a couple of minutes," says Michlovic. "Currently, there's no toxic gasses-developed criteria for plenum-rated cable, no fuel load standard. Worst of all, there are no toxicity standard and no acid level requirements."
Current industry estimates: 1,000 feet of four-pair unshielded twisted pair (UTP) cable weighs about 24 pounds -10 pounds of copper and 14 pounds of plastic jacketing and insulation.
"When cables are installed in a plenum air handling space, exposure to airflow makes the risk from heat or fire generated toxic gasses and smoke especially dangerous for building occupants when fire breaks out," says John Moritz, principal of JMME consulting firm, well-known safety advocate and NFPA/NEC expert.
Fluoropolymer (like DuPont Teflon® FEP) insulated and/or jacketed cabling releases many toxic gases under heat decomposition. Some of the deadly gasses like Hydrogen Fluoride are highly reactive. HF gas, when in contact with any moisture, including humidity, forms hydrofluoric acid. Moritz said, "Hydrofluoric acid is so corrosive that it can destroy most glass and eat away most metals and metal oxides. The damage potential posed by HF to the human body is immediate and it can affect your eyes, throat, and lungs incapacitating someone on exposure. Incapacitation can and does lead to many fire related causalities." Remember: Safety is too important to ignore.