The DOT ERG identifies chemicals as being shipped “inhibited” or “stabilized” and have a “P” listed with their guide number meaning that the chemical can polymerize. These inhibitors are TIME and TEMPERATURE dependent! The inhibitors can be tested and more inhibitor added if necessary, albeit VERY RISKY once the reaction has begun AND the fact that these inhibitors are not something First Responders have readily available. This week we learned that the inhibitor used in styrene, UN2055, is 10 to 50 ppm of tertiary butyl catechol (4-tertiary-butyl-catechol), with the higher concentration for higher storage temperatures. Here is a listing of other chemicals that can polymerize as the Styrene did in Selkirk, NY this week.
Butadienes, UN1010, readily self-polymerizes and can also form explosive peroxides with air unless inhibited, and it is illegal to ship butadienes without an inhibiting agent (tributylcatechol, di-n-butyl amine, or phenyl-betanaphthylamine). For an account of a butadiene explosion involving a 500 kg cylinder at a Japanese chemical plant, see http://shippai.jst.go.jp/en/Detail?fn=0&id=CC1200052&kw=Environment.
The butadiene polymerized within the safety release valve of the partly full cylinder, which caused it to clog. When the cylinder was left outside exposed to sunlight, the pressure built up within the cylinder and it exploded. A summary of salvage operations following the gas tanker Igloo Moon incident, where the tanker ran aground outside Key Biscayne, Florida, within the Biscayne National Park boundary, on 6 November 1996 is at http://www.kustbevakningen.se/ra/volume2/annex3accidents/igloo.htm.
The gas tanker contained 6589 tonnes of compressed and liquefied butadiene. Many different salvage operations were considered, and plans for public evacuations were set up for various situations that could go wrong. The salvage plan chosen included bringing another vessel (the Selma Hosan) alongside the Igloo Moon which had runaground; approximately 1000 tonnes of butadiene were transferred between November 20 and 21 to the Selma Hosan, which was enough to lighten the load so that the stricken gas tanker could be refloated during the flood tide. The plan included monitoring the inhibitor concentration so the butadiene would not polymerize, which would have been catastrophic. No chemicals were released to the water.
Ethylene oxide, UN1040, may self-polymerize in the presence of a small amount of water, and many common metals (except stainless steel and nickel containers) can initiate the polymerization; sometimes 0.1% hydroquinone (an anti-oxidant) is added as an inhibitor.
Propyleneimine, UN1921, and Ethyleneimine, UN1185, readily polymerizes in contact with acid or acid fumes, and is sensitive to air, sunlight, and/or heat; solid sodium or potassium hydroxide is added as an inhibitor to scavenge any acid.
Furural or furfuraldehydes, UN1199, can undergo exothermic polymerization in contact with acid or alkali; ignition can occur spontaneously with sodium bicarbonate (baking soda). Exposure to light and air darkens the chemical. The inhibiting agent for this chemical may be dialkylphenylenediamine or butylated hydroxytoluene (BHT).
Vinyl acetate, UN1301, is another chemical that can undergo bulk polymerization in storage vessels. This polymerization is extremely violent and may generate a pressure surge of over 40 atmospheres due to the monomer vapor pressure, enough to explode the vessel. The polymerization may be initiated by exposure to small amounts of peroxide; the peroxide may be formed by exposure of the chemical to oxygen in the air. The inhibitor is usually 3 to 20 parts per million (ppm) of hydroquinone or methyl hydroquinone to scavenge free radicals (peroxides). Less hydroquinone is added if the vinyl acetate is to be used soon, and more hydroquinone is added if the vinyl acetate is to be stored for several months before use. Diphenylamine might be used as an inhibitor for prolonged storage. Details on this chemical may be found in a rather technical paper, Jean-Louis Gustin and. F. Lahanier, “Understanding Vinyl Acetate Polymerization Accidents”, Organic Process Research & Development, 2005, vol 9, p 962-975, which can be obtained from the Internet at
http://pubs.acs.org/cgi-bin/sample.cgi/oprdfk/2005/9/i06/pdf/op050097f.pdf
An account of an exploding drum of vinyl acetate stored in an industrial facility is at http://shippai.jst.go.jp/en/Detail?fn=0&id=CC1000176.
Hydrogen cyanide, UN1051, is another chemical that can undergo self-polymerization releasing heat. The container could fail because of increasing container pressure as it is heated releasing lethal hydrogen cyanide gas. If the temperature exceeds about 260-265oC (about 520oF), the chemical can detonate. A mineral acid inhibitor (such as phosphoric acid) is usually added to prevent polymerization.
Source: https://www.aristatek.com/Newsletter/OCT08/TechSpeak.pdf