Climate ChangeAs noted in Healthy Building Network’s(HBN) Chlorine and Building Materials report, chlorine production is a major source of releases of carbon tetrachloride, a potent global warming and ozone depleting gas as well as a carcinogen.
As the report reminds us, it’s important to consider not only the use-phase impacts of building products, but the entire life cycle, including primary chemical production that’s several steps back from final product manufacture.
Blowing agents are used in plastic foam insulation to create the foam structure and also contribute to the insulative properties. Over the years, manufacturers have cycled through a range of fluorocarbons as each prior class is phased out due to environmental concerns – from ozone depleting chlorofluorocarbons (CFCs) to less ozone depleting hydrochlorofluorocarbons (HCFCs) to the non-ozone depleting but high global warming potential hydrofluorocarbons (HFCs) currently common in many types of foam insulation. Manufacturers have now begun the latest shift to next generation, low global warming potential hydrofluoroolefins (HFOs). For extruded polystyrene (XPS), this translates to a shift from commonly used HFC-134a with a global warming potential (GWP) of 1,430 to HFO-1234ze with a GWP of six.2
The summary of these chemical transitions only tells part of the story. While HFOs do not directly deplete the ozone layer or significantly contribute to global warming, many HFOs use carbon tetrachloride (CCl4) as a chemical feedstock. This includes HFO-1234ze, the replacement for HFC-134a (which does not use CCl4) in many applications.3
How is it that this ozone depleting substance is still in use? Many uses of carbon tetrachloride were phased out in 1995, under the terms of the Montreal Protocol to protect the ozone layer. But the Montreal Protocol phase-outs exempted the use of CCl4 as a chemical feedstock, under the assumption that emissions would be minor.4 However, carbon tetrachloride “is not decreasing in the atmosphere as rapidly as expected” based on its known lifetime and emissions, according to a 2016 report on the Mystery of Carbon Tetrachloride. The authors of this report concluded that emissions of carbon tetrachloride during its production, and fugitive emissions from its use as a chemical feedstock, have been significantly unreported and underestimated.5
Production of carbon tetrachloride is likely to increase as industry replaces HFC blowing agents (and refrigerants), most of which aren’t produced with carbon tetrachloride, with HFOs that do use CCl4 as a feedstock.[6] With increased production and use of carbon tetrachloride, increased emissions are expected – and that’s bad news for the earth’s recovering ozone layer.
We recommend against the use of plastic foam insulation whenever possible, but if you do use it, some products are available that use other, less impactful, blowing agents, including hydrocarbons and water. For more recommendations about preferable insulation from a health hazard perspective, review our product guidance at informed.habitablefuture.org.
READ HABITABLE’S NEW REPORT