What is Polyurethane?

Peter Lord asks:

The fire at the West Warwick, Rhode Island nightclub at which ninety-nine people died this February, when polyurethane soundproofing caught fire, was horrific. What might have produced the toxic fumes that news reports said were released in the fire? What is polyurethane made from, and where/in what is it used?

Peter Lord,
Providence, RI

The Green Guide Responds:

We had the same questions as we read the press accounts of this cruel tragedy. It underscores the particular dangers of inhaling smoke from burning plastics, which are made from petrochemicals and, in some cases, highly toxic organic compounds. The foam used in the nightclub fire was marketed as a packaging material, but was used for sound-proofing; it contained no fire-retardants.

As for the polyurethane itself, in 1937, the German scientist Otto Bayer first produced the substance while searching for substitutes for natural rubber. Today, it comes in many basic forms including elastomers, coatings, flexible foams and rigid foams. Elastomers are flexible but return to their original shape and are found in roller skate wheels, ski boots, and, as a fiber, spandex. Coatings appear on dancefloors and bowling alleys and polyurethane paint is found on cars and planes. The flexible foams, making up the largest polyurethane market, appear in mattress padding, foam cushions, automobile dashboard liners, packaging, and carpet backing. Lastly, rigid foams are used to make insulation laminate panels.

Polyurethane is actually another name for the family of chemicals known as the urethane polymers, which are composed of two principal raw materials, isocyanates and polyols, brought together with catalysts and a large variety of additives. Isocyanates are highly reactive; the two most commonly used in polyurethane production are toluene diisocyanate, (TDI) made from chlorine, toluene, phosgene, sulfuric acid, and nitric acid, all hazardous volatile organic compounds (VOCs), and methylene diphenyl diisocyanate (MDI), made from formaldehyde, sulfuric acid, nitric acid, phosegene, and benzene. In terms of environmental impacts, to make one kilogram (kg) of polyurethane rigid foam it takes an estimated 361 kg water, .98 kg natural gas, .69 kg crude oil, .41 kg coal, 19618 mg methane (CH4), according to the Association of Plastics Manufacturers in Europe. Meanwhile, production of this kilogram of rigid foam emits wastes including 3.7 kg of carbon dioxide, a major global warming gases, .5 kg chlorine ion and .29 kg sodium ion into water, .35 kg solid mineral waste. The numbers are similar for flexible foam. In terms of potential health effects, the neurotoxin toluene can offgas from the mattresses and other products . Phil Landrigan and Herbert Needleman note in Raising Healthy Children in a Toxic World (Rodale, 2001), that, when inhaled, the TDI in floor finishes "can cause airways sensitivity, and reexposure to TDI can cause chemically induced asthma."

The other principle polyurethane raw material, polyols, are compounds containing multiple hydroxyl groups (O-H groups). Frequently used polyols include various polyester and polyether glycols. As for additives, ozone-depleting chlorofluorocarbons (CFCs) were formerly used to produce softer, lower density foams; the industry moved towards methylene chloride, but the EPA is also limiting its use since chronic exposure may damage the nervous system and it is considered a probable human carcinogen. Despite these lifecycle issues, Greenpeace argues that polyvinyl chloride (PVC), which releases toxic dioxins when manufactured and burned, and often contains toxic plasticizing chemicals known as phthalates, is worse than polyurethane. Also, recycling programs do exist for polyurethane foams, but most programs do not accept PVC.

However, when it comes to fire safety, polyurethane foam has been regarded as a problem for some time. In 1989, OSHA issued a memorandum on the fire hazards of rigid polyurethane foam insulation noting that "when ignited, [these foams] burn rapidly and produce intense heat, dense smoke and gases which are irritating, flammable and/or toxic. As with other organic materials the most significant gas is usually carbon monoxide." The memo goes on to note that whether or not they contain fire retardants, all organic cellular plastics should be considered combustible. Terms such as "flame-resistant" and "self-extinguishing," according to the OSHA memo, are only valid measures under small fire exposures and do not take into consideration "large scale fire conditions." Following the Rhode Island nightclub fire, OSHA performed tests on samples of the polyurethane foam found in the club's basement, coming up with a long list of toxic chemicals. At 450 degrees C. (the temperature at which the foam smolders), smoke contained carbon dioxide, TDI, glycol ethers and related compounds, styrene (a neurotoxin and possible carcinogen), phenol butyronitrile, and "compounds not found in mass spec libraries" (meaning unidentified complex chemicals). At 750 degrees C. (combustion temperature), smoke contained CO2, propene, acrylonitrile, acetone, hydroxy acetone, glycol ethers, toluene (a neurotoxin), ethyl benzene, styrene, small amounts of benzene (a known carcinogen and neurotoxin), toluene isocyanate, TDI, phenol butyronitrile and "compounds not found in mass spec libraries." Kipp Hartmann, OSHA area for Rhode Island, says OSHA performed the tests to assist health officials in their diagnosis of patients suffering with lung complaints after the fire.

While lawsuits rage against the nightclub owners, the company that produced the polyurethane foam, and others, the lesson of this terrible fire is clear: polyurethane foam insulation, when used in building, must be installed properly, using the fire resistance measures stipulated by your local building codes. Public education and building codes, however, cannot prevent these tragedies or the misuse of materials. As OSHA noted in 1989 all organic cellular plastics, of which polyurethane is only a variety, are combustible. Perhaps it is time we reconsidered how we insulate our buildings and whether a cheap material is really worth the long-term dangers. For safer insulation materials, see "Is Polyurethane Foam Insulation Safe?" . In addition, those with allergies and/or asthma, may want to choose polyurethane-free mattresses and furniture, made with organic cotton or chemical-free wool, and latex rubber in the core if latex allergies are not a problem. (See "Fresh, Nontoxic Takes on Home Decor" in GG90).