Beware the Hidden Ozone Depleter: Upstream Impacts of Blowing Agents

Rebecca Stamm | August 14, 2018

As noted in HBN’s new 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.[1] As this 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. In our 2017 comments to the EPA, HBN uncovered another link to ozone depleting carbon tetrachloride in building products – one you might not expect – use in the production of low global warming potential blowing agents.

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. Now, manufacturers have 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.

HBN recommends 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 recommendations on HomeFree.


[1] According to US Toxics Release Inventory (TRI) data from 2012 to 2015, half of the 10 leading sources of carbon tetrachloride releases were chemical complexes with chlor-alkali plants. Reporting from other countries is non-existent or incomplete. The European Pollutant Release and Transfer Register (E-PRTR) contains no reported emissions of carbon tetrachloride from chlorine plants in the European Union between 2012 and 2016. Manufacturers are required to report carbon tetrachloride releases in excess of 100 kg per year, however, European scientists tracking carbon tetrachloride emissions say the industry is likely not reporting emissions. A 2016 report estimated that the chlor-alkali industry worldwide was responsible for about 10,000 metric tons of unreported carbon tetrachloride releases, or about 40% of all unreported carbon tetrachloride releases.

[2] “Comments to the U.S. Environmental Protection Agency (EPA) on the Scope of Its Risk Evaluation for the TSCA Work Plan Chemical: CARBON TETRACHLORIDE (CTC) CAS Reg. No. 56-23-5.” Safer Chemicals, Healthy Families; Environmental Health Strategy Center; Healthy Building Network, March 15, 2017.; “Common Product: XPS Insulation (Extruded Polystyrene).” Pharos Project. Accessed February 1, 2017.; “Substitutes in Polystyrene: Extruded Boardstock and Billet.” United States Environmental Protection Agency: Significant New Alternatives Policy (SNAP). Accessed July 26, 2018.

Global Warming Potential (GWP) defined — Certain gasses, commonly referred to as “greenhouse gasses”, have the ability to warm the earth by absorbing heat from the sun and trapping it in the atmosphere. Global warming potential is a relative measure of how much heat a given greenhouse gas will absorb in a given time period. GWP numbers are relative to carbon dioxide, which has a GWP of 1. The larger the GWP number, the more a gas warms the earth. Learn more about interpreting GWP numbers at understanding-global-warming-potentials.

[3] Liang, Q., P.A. Newman, and S. Reimann. “SPARC Report on the Mystery of Carbon Tetrachloride.” Stratosphere-troposphere Processes and their Role in Climate, July 2016. Report7_2016.pdf.

[4] Vallette, Jim. “Chlorine and Building Materials: A Global Inventory of Production Technologies, Markets, and Pollution - Phase 1: Africa, The Americas, and Europe.” Healthy Building Network, July 2018.

[5] Liang, Q., P.A. Newman, and S. Reimann. “SPARC Report on the Mystery of Carbon Tetrachloride.” Stratosphere-troposphere Processes and their Role in Climate, July 2016. Report7_2016.pdf.