The walls of refrigerators have to be heavily insulated in order to maintain efficient cooling. Polyurethane foam insulation has been the classic material used for this purpose and guess what it used to be 鈥渂lown鈥� with? Chlorofluorocarbons! Foams are created by blowing a gas into an appropriate substance to form bubbles. Of course the gas must not react with the material, and in the case of insulation, should not transmit heat. CFCs, the same substances used as refrigerants, were ideal, at least until their environmental consequences were discovered. Legislation was then introduced that called for the removal of the refrigerant from any discarded refrigerator. But, surely surprising to most people, far more CFCs were used for foam blowing than for refrigeration. A typical fridge may have a couple of hundred grams of refrigerant but can hold twice as much blowing agent captive in its insulation. And 鈥渃aptive鈥� is the appropriate expression because studies have shown that more than 90% of the original blowing agent is still present in a refrigerator fifteen years after it has been discarded. Unless special methods are employed, when such fridges are recycled for their metal content, the blowing agent is released to the atmosphere. Shredding the fridge into small pieces in an airtight chamber allows the blowing agent to be recovered. This technique is expensive but can offer huge environmental benefits. Currently manufactured refrigerators do not present this problem. The insulation gas now used is cyclopentane which has no effect on ozone depletion and has a negligible global warming effect. CFCs as refrigerants were replaced in the 1990s by HFCs (hydrofluorocarbons) which do not damage the ozone layer but still contribute to the greenhouse effect. Some manufacturers are now switching to isobutane as refrigerant, because like cyclopentane, it has a minimal impact on the environment. Given that millions and millions of discarded fridges are stockpiled around the world, the problem associated with the CFC content of their polyurethane foam insulation is not a trivial one.
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