Revisiting Rigid Foam Insulation and Ozone
A great deal has happened since we addressed “rigid foam insulation and the environment” ten years ago this month (
Vol. 1, No. 1). The big issue then was ozone depletion, and that continues to be the most significant driver of change. Of the three common types of rigid foam boardstock insulation, two of them—polyisocyanurate (polyiso) and extruded polystyrene (XPS)—are (or were) made with CFCs and HCFCs, blowing agents that affect the ozone layer. The third type, expanded polystyrene (EPS), has long been made with an ozone-safe blowing agent.These chemicals, CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons), break down ozone when high-energy ultraviolet light breaks apart the CFC or HCFC molecule, releasing free chlorine atoms that react with ozone (O
3). A single CFC or HCFC molecule can destroy many thousands of ozone molecules. Due to their shorter life and fewer chlorine atoms, HCFCs are just 5 to 11% as damaging to stratospheric ozone as CFCs. (Note that compression-cycle chillers, air conditioners, heat pumps, and refrigerators also use CFCs and HCFCs as refrigerants—see
Ozone depletion is important because the stratospheric ozone layer protects life on Earth from the harmful effects of high-energy ultraviolet radiation (UV-B). Each 1% reduction in stratospheric ozone increases exposure to UV-B by 1.5 to 2%, according to the U.S. Environmental Protection Agency (EPA). Exposure to UV-B (radiation at wavelengths between 280 and 320 nm), can result in human eye damage and skin cancer as well as significant damage to plants (including agricultural crops) and wildlife (particularly aquatic organisms).
Back in 1992, manufacturers of polyiso and XPS were in the process of switching from the really bad CFC blowing agents to less damaging HCFCs. The 1987 Montreal Protocol called for a phaseout of most nonessential uses of CFCs by 1996. Five separate amendments to the Montreal Protocol (London, 1990; Copenhagen, 1992; Vienna, 1995; Montreal, 1997; Beijing, 1999) sped up this CFC phaseout and added a phaseout timeline for HCFCs. Each signatory nation had to develop a specific plan for implementing the Montreal Protocol; in the U.S. the 1990 Clear Air Act provided the enabling legislation, and the EPA developed the specific regulations.
In 1992, all polyiso was produced with the blowing agent CFC-11. A number of chemicals had been considered as substitute blowing agents, and toxicity testing was under way on the most likely replacement: HCFC-141b. The first manufacturer to switch to HCFC-141b, NRG Barriers (now owned by Johns Manville), did so in January 1993 (see
Vol. 2, No. 1), and the entire industry completed the transition by mid-1993.
Today, the polyiso industry is struggling with yet another transition: replacing the HCFC-141b with a zero-ozone-depletion blowing agent, as called for by EPA. (Among HCFCs, EPA opted to phase out those with highest ozone depletion potentials [ODPs] the quickest.) HCFC-141b, with an ODP of 0.11, can no longer be sold in the U.S. after December 31, 2002. Atlas Roofing, in February 1998, became the first company to introduce a polyiso product meeting the 2003 standard (see
Vol. 7, No. 5). Jared Blum, president of the Polyisocyanurate Insulation Manufacturers Association (PIMA), reported that the industry is on track to complete the phaseout on schedule. Every manufacturer of polyiso is now operating at least one plant converted to “third-generation” blowing agents, according to Blum. While manufacturers will be permitted to stockpile HCFC-141b and continue to use it after January 1, 2003, “we have every confidence that the industry will be converted in the first quarter of ’03,” Blum told
EBN. “The march is on.”
While various non-ozone-depleting blowing agents were investigated for polyiso production, Atlas led the way with a hydrocarbon mix, and manufacturers are universally adopting that approach, according to Blum. Making the switch has required substantial retooling (especially since hydrocarbons are highly flammable). Although the new blowing agents are cheaper, costs of ensuring plant safety and insurance coverage are higher. In addition to the ozone benefits of hydrocarbon blowing agents, they are not greenhouse gases, so do not contribute to global warming. By contrast, HCFCs and HFCs (hydrofluorocarbons)—the other class of substitute blowing agents (and refrigerants)—are significant greenhouse gases (see Table 2).
Extruded PolystyreneIn 1992, the four U.S. manufacturers of XPS were making good progress on the transition from CFC-12 to HCFC-142b. Because HCFC-142b had already undergone toxicity testing, substitution could begin quickly. Amoco Foam Products (now owned by Pactiv) and Dow Chemical had completed the switch by 1990. The other two manufacturers, UC Industries (producer of FoamulaR—since purchased by Owens Corning) and Diversifoam Products, were still converting their plants to HCFC in mid-1992.
While polyiso has to convert to third-generation blowing agents in the next year, the U.S. XPS industry is not under the same pressures. HCFC-142b does not have to be completely phased out until 2010. To date, no U.S. manufacturer has made the switch.
By contrast, Europe has already eliminated the use of HCFC-142b, replacing it either with HFC-134A or carbon dioxide. According to Patrick Rynd, the leader of science and technology for foam at Owens Corning, life-safety codes and different product dimensions in the U.S. prevent XPS manufacturers from following suit. Europe has a primarily “high-density” market, with structural performance more important than thermal performance, Rynd reported. He said that if they had to implement the European approach here, the XPS density would increase significantly, resulting in a conflict with life-safety codes concerned with fuel loading: “We literally could not convert today because of the issue of density.” The fact that most XPS is manufactured at 4’ (1,200 mm) widths—vs. 2’ (600 mm) in Europe—also makes conversion much more difficult. The industry is working hard on the transition, said Rynd, but meeting the 2010 deadline will be a challenge.
Is All This Making a Difference?It appears that the international efforts to keep human-generated chlorine and bromine (halogens) out of the stratosphere have had a major effect. In 1998, the United Nations Environment Programme (UNEP) and World Health Organization (WHO) reported that “the total combined abundance of ozone-depleting compounds in the lower atmosphere peaked in about 1994 and is now slowly declining.” Because it takes a while for ozone-depleting substances to drift up to the stratosphere, chlorine and bromine levels in the stratosphere were projected to peak by 2000.
One of the most measurable impacts of ozone depletion is the ozone hole above the Antarctic that was first reported in 1985. Recent data from the British Antarctic Survey (see graph below) shows that the annually appearing reduction in ozone levels (measured in Dobson units) appears to be leveling off, consistent with UNEP/WHO projections. Most scientists are unwilling to project how quickly the stratospheric ozone layer will recover, however—the drop in halogen levels in the stratosphere might be slower than the buildup had been.
Factors such as volcanoes, nitrous oxide, methane, and water vapor might slow that recovery.
For more information:Polyisocyanurate Insul. Manufacturers Assoc.
Office of Air & Radiation
Published July 1, 2002 Permalink Citation
(2002, July 1). Revisiting Rigid Foam Insulation and Ozone. Retrieved from https://www.buildinggreen.com/newsbrief/revisiting-rigid-foam-insulation-and-ozone
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