STYRENE
HAZARDOUS MATERIALS
CHEMICAL DATA NOTEBOOK SERIES #47
Styrene is an unstable, reactive, flammable, somewhat corrosive, toxic, clear, colorless, oily liquid with a sharp, pungent odor. It is a monomer for polystyrene, and as such is an intermediate for other polymers, which may be classified as rubber, plastic, coatings, or paints. It is copolymerized with butadiene to form styrene-butadiene rubber (SBR), which is produced at higher quantities than any other synthetic rubber. It is also used in the manufacture of some drugs. Styrene is a carcinogen.
PROPERTIES
Styrene has a flash point of 88°F, an ignition temperature of 914°F, and a flammable range of 1.1 percent to 7.0 percent in air. It has a specific gravity of 0.906, a molecular weight of 104, and a vapor density of 3 59It boils at 293°F, freezes at – 23.8°F, and is very slightly soluble in water. Its chemical formula is C6H5C2H3 (sometimes written C6H5CH = CH2 or C6H5CH:CH2), and its structural formula is [The hexagonal structure with the circle in the middle is the shorthand method for drawing the molecular structure of benzene; when it is attached to another atom (other than hydrogen) as shown, it is the phenyl radical. The other part of the molecular structure of styrene is known as the vinyl radical, and it is derived from ethylene—hence, the synonyms vinyl benzene and phenylethylene ]
HAZARDS
Styrene’s major commercial value is as a monomer for polystyrene or as a comonomer for other plastics, rubber, coatings, and paints. Because it is a monomer and will polymerize, it must be prevented from doing so during transportation and storage. The polymerization reaction of styrene (and other monomers) involves the breaking of double bonds, which releases energy in the form of heat. This heat is absorbed by the surrounding monomer, raising its temperature, which speeds up the polymerization reaction and the subsequent breaking of more double bonds and the releasing of more heat.
A rule of thumb in controlling chemical reactions says that for every 18°F (10°C) rise in temperature, the speed of the reaction will double. Once the cycle has begun, and the reaction speed continues to double as the temperature rises, the reaction will proceed so fast and the energy released becomes so massive that the entire aggregate explodes. Inside a reactor within a polymerization plant, this polymerization reaction is controlled by the chemical engineers and process equipment and is therefore safe. However, if the reaction is allowed to proceed outside of the proper equipment, as in storage or in a transportation accident, the result of this uncontained reaction is called a runaway or uncontrolled polymerization.
Because of this ability to react with itself, usually because it has become heated or contaminated, styrene must be considered an unstable chemical. To prevent an uncontrolled polymerization reaction from occurring, a small amount of a chemical that can stabilize styrene against this reaction is added. These chemicals—and there are many different chemicals used to stabilize different monomers—are called inhibitors. As long as the inhibitor remains mixed uniformly throughout the monomer, the monomer will be stable and safe.
However, in an accident resulting in a release of the monomer, the inhibitor may be forced out of the monomer or overcome by a contaminant. Once the inhibitor is gone or reduced to an amount where it becomes ineffective, the monomer once again becomes unstable and subject to polymerization. Indeed, this is what the chemical engineer does in the reactor to start the polymerization process: Another chemical, called an initiator, overcomes the inhibitor, and the reaction proceeds in a controlled and safe manner. In the reactor the result is the polymer called polystyrene, but in the street the initiator is a contaminant whose reaction with styrene may lead to explosion and fire.
Some references classify styrene as a stable chemical, and it is — if properly stabilized and kept at safe temperatures. However, its ability to polymerize, especially in an accidental release, makes it an unstable chemical as tar as emergency responders are concerned. It is a storage hazard at temperatures above 89°F.
Styrene, when exposed to oxygen at temperatures above 104°F, will form highly unstable and explosive peroxides. The organic peroxides are the compounds most likely to act as unintentional initiators capable of instigating explosive runaway polymerization, but styrene is also very reactive with many chemicals. Among these are glycols, the halogens and the halogen halides, inorganic acids, metal salts, oxidizers, strong bases such as sodium hydroxide, and strong acids such as chlorosulfonic acid and sulfuric acid, all of which may cause a reaction that overpowers the inhibitor and initiates polymerization. Styrene is also corrosive to copper and copper alloys.
Styrene’s flash point of 88°F classifies it as a flammable liquid, and its relatively high vapor density of 3-59 means that its vapors will “hang together” for a long time (unless dispersed by a breeze or some other disturbance). These vapors, being fluid, will flow along low areas in the terrain, accumulating in low, protected areas and/or confined spaces. These “pockets” of vapor will be very hazardous, since any common ignition source can provide the energy required to reach styrene’s ignition temperature and cause these vapors to explode.
The rather low lower flammable limit of 1.1 percent in air means that it doesn’t take much material to form an ignitable mixture. The vapors, after the original explosion, will ignite and flash back along its own trail to the source of the vapors. Anyone within this “vapor trail” will be caught in this flash of fire.
SYNONYMS
benzene, vinyl-
cinnamene
cinnamenol
cinnamol
Diarex HF 77
ethenyl benzene
ethylene, phenyl-
NCI-c02200
phenethylene
phenylethene
phenylethylene
styrene monomer
styrene monomer, inhibited
Styrol
Styrole
Styrolene
Styron
Styropol
Styropor
vinylbenzene
vinylbenzol
Styrene is considered a moderately toxic material, its carcinogenicity notwithstanding. Rather low concentrations (its odor may be detected as low as 0.02 ppm) of 200 ppm (parts per million of air) will cause eye irritation, possible severe eye injury, and upper respiratory tract problems. Higher concentrations can cause death due to respiratory paralysis, with intermediate symptoms including cramps, dizziness, drowsiness, headache, intoxication, and eventually unconsciousness caused by narcosis and depression of the central nervous system. Styrene’s TLV-TWA (threshold limit value-time weighted average) is 50 ppm; its STEL (shortterm exposure limit) is 100 ppm; and concentrations near 400 ppm can cause problems in under an hour.
Contact of the liquid with the eyes can cause injury to the cornea, and repeated contact with the skin can cause cracking and irritation by defatting action. Ingestion of small amounts of styrene causes symptoms of narcosis.
NONFIRE SCENARIO
Notify environmental authorities of any release of styrene or any other hazardous material even before emergency responders arrive on the incident scene. This should be done even if positive identification has not been made, since placarding and other clues such as labels, the shape of the container, unusual smells, or the presence of people showing adverse reaction to exposure to the material indicate the presence of a hazardous material. Even if the released material turns out to be nonhazardous, it is always better to err on the side of conservatism.
If liquid is leaking from the container or has already spilled onto the ground, evacuation downwind is an immediate concern because of styrene’s high vapor density, low ignition temperature, and toxic and irritating properties. At low concentrations, the odor may be sweet and pleasant (and therefore interpreted as nonhazardous) but rapidly becomes sharp and pungent as the concentration of vapors increases. Exposed persons may become incapacitated because of tearing eyes and heavy coughing.
Since styrene is a flammable liquid, approach from upwind, identify and eliminate all ignition sources, and keep everyone without respiratory protection away from the danger zone. After an initial search for and elimination of ignition sources, prepare for wind shifts that might occur.
Care must be taken with any styrene liquid that may have been released from its original container. Any contact with the material will contaminate it, and it will be sensitized and ready to polymerize. The occurrence of this reaction in the open is not as dangerous as if the liquid were confined, but enough heat will be generated to volatilize the liquid, increasing the amount of vapors present in the air that could ignite and explode. The source of ignition could be the heat energy released from the liquid itself as the reaction speed increases.
IDENTIFICATION NUMBERS AND RATINGS
CAS
(Chemical Abstract Services)
100-42-5
STCC
(Standard Transportation Commodity Code)
4907265
RTECS
(Registry of Toxic Effects of Chemical Substances)
WL3675000
UN/NA
(United Nations/North America)
2055
CHRIS
(Chemical Hazard Response Information System)
SIT
DOT
(U.S. Department of Transportation)
Flammable liquid
NFPA 704 Rating
(National Fire Protection Association)
2–3-2
IMO
(International Maritime Organization)
3 3, flammable liquid
Water spray or fog may be used to disperse styrene vapors. Be sure to contain the runoff water created from this mitigation technique.
Emergency containment ponds may be constructed by diking earth, clay, sand, or other absorbent material around the spilled material. If the proper equipment is available, a containment pond may be dug to hold the styrene. In both cases compatible tools and equipment must be used— the tools and equipment are made of material that will not be attacked by the product and that is nonsparking. In addition, all electrical equipment must be explosionproof — no flammable vapors may be exposed to any electrical sparks generated by the electrical motors or batteries. Catch basins and other entries to the sewer system also must be blocked. Once the liquid is contained, professional salvage personnel may suction it from the containment pond or pit and place it in secure containers.
Most emergency responders have not been properly educated, trained, or equipped to perform salvage and/ or cleanup functions at hazardousmaterials incidents. It would be tragic to have a group of firefighters successfully handle a dangerous hazardousmaterials release by protecting the lives, environment, systems, and property in their response district, only to be seriously injured or killed in a salvage or cleanup operation.
While specially trained professionals perform salvage and cleanup, the environmental authorities must decide how much soil has to be removed, depending on how far and/or how deep the contaminating material may have traveled. Any liquid remaining in the pond or pit after the suctioning-out process may be absorbed with powder, clay, fly ash, hay, peat, sand, sawdust, soil, straw, or other sorbent material. This absorbed material must be handled carefully since it contains styrene liquid, and it must be disposed of in accordance with federal, state, and local regulations.
Steps must be taken to prevent styrene from entering sewers or waterways. If styrene enters a sewer system, explosive vapors will be generated and may spread throughout the system, threatening the entire community with an explosion. Of course the vapors, like the liquid, will flow from high to low grade, but they will also move upward once the system downgrade is “filled” with vapors. Alert all sewage treatment facilities immediately.
If styrene enters a waterway, the liquid, since it is only very slightly soluble in water and has a specific gravity of 0.906, will float on the surface of the water. Alert all downstream users of the water immediately, and make sure all water use is discontinued until the environmental experts declare that the water is safe for use.
Techniques used to skim or otherwise remove oil from a waterway, such as containment booms, surfaceskimming devices, bypass dams, and adsorbents, may be used to remove styrene from the water. Bypass dams are devices that allow water to flow but stop substances on the surface from passing. They can be built by placing pipes or a conduit well below the surface of the water, which allows the subsurface water to pass through and keeps material on the surface from flowing downstream.
If there are any low-lying areas next to the waterway, the water may be diverted into them rather than flow downstream. This technique allows the removal of any dissolved product or any product floating on the surface. Once the contaminated water has been diverted out of the waterway bed and contained, skimming techniques can remove styrene on the surface, and activated charcoal gently mixed into the water can adsorb the dissolved styrene. Absorption techniques will remove the floating contaminant. Agitation of the water and aeration techniques also may remove the dissolved product.
Care must be taken in the disposal of all adsorbents or absorbents used, since the flammable material is still present. The other techniques, especially agitation and aeration, force the dissolved styrene out of the w’ater, and explosive vapors may be present. The environmental authorities on the scene must monitor purification techniques, which are carried out by professional personnel trained in those techniques. These environmental experts will continuously test the water downstream to determine when it is safe for use.
Water for industrial use must also be certified as safe. If water contaminated by styrene is allowed to enter an industrial operation and it comes in contact with hot surfaces or equipment, a dangerous vapor accumulation might occur.
FIRE SCENARIO
Any sealed containers of styrene that are exposed to flames or the radiated heat of a fire will be subject to a catastrophic failure due to the rapid pressure rise caused by absorbed heat energy from the fire. The failure will be explosive; in essence it will be a BLEVE. Use flooding amounts of water to cool such containers, and deliver the water from as far away as possible using unmanned appliances. Firefighters must never let themselves be caught between a fire and containers that might explode when exposed to heat.
Any pressure-relief valve present on the heated containers will be venting flammable vapors, and they will almost always be ignited, adding additional heat energy and danger. The danger of a BLEVE from impinging flames is bad enough, but remember that styrene is a monomer as well as a flammable liquid: Exposure to heat will sensitize the monomer by overcoming the stabilizing effect of the inhibitor (as well as possibly driving the inhibitor completely out of the monomer), and a violent, explosive, runaway polymerization may be imminent. Regardless of which explosion occurs (and by what mechanism), the results will be disastrous.
Water may be used to extinguish burning styrene if it is applied in the proper manner. High-pressure water spray may be effective if it is applied in the same manner as when used against any other burning flammable liquid. Foam may be used to blanket the burning liquid if it can be applied in the quantities appropriate for the volume of the liquid burning. Dry chemical and carbon dioxide may be used on smaller fires if the proper terrain and atmospheric conditions exist.
PROTECTIVE CLOTHING AND EQUIPMENT
Choose clothing and protective equipment that prevent contact of ethyl alcohol liquid or vapor with the eyes, skin, or respiratory system. Select splashproof chemical goggles and a face shield for eye protection, and use positive-pressure, self-contained breathing apparatus. Rubber boots, gloves, and aprons and other impervious clothing will offer protection. Manufacturers of total encapsulating suits claim that material such as polyethylene, polyvinyl alcohol, and Viton may offer protection.
FIRST AID
For inhalation, remove the victim to fresh air. If the victim has stopped breathing or breathing has become difficult, administer artificial respiration (mouth-to-mouth resuscitation may expose the provider of first aid to the material in the victim’s mouth or vomit). Provide medical attention immediately.
For ingestion, do not induce vomiting. Call for immediate medical attention while making sure the victim is warm and comfortable.
For skin contact, remove all contaminated clothing and wash all affected body areas with large amounts of water. Medical attention is necessary if irritation of the skin persists.
For eye contact, flush the eyes immediately with large amounts of water for 15 minutes, occasionally lifting the eyelids. Provide medical attention immediately.
GLOSSARY
Alloy—a physical mixture, usually of metals, created by melting the metals together. Alloys are not chemical compounds. ‘They also may be mixtures of polymers.
BLEVE—acronym for boiling-liquid, expanding-vapor explosion.
Comonomer—a monomer polymerized with another monomer to form a copolymer. The copolymer will have many of the properties of each polymer if the monomers were polymerized separately.
Halogen—a family of elements (Group VI1A on the Periodic Table of the Elements). The halogens are fluorine, chlorine, bromine, iodine, and astatine, which is very rare.
Hydrogen halide—a binary compound of hydrogen and a halogen: the acid gases; hydrogen fluoride, hydrogen chloride, hydrogen bromide, and hydrogen iodide.
Inhibitor or stabilizer—a chemical added to another material that will keep an unwanted reaction from occurring (allow it to remain stable). In monomers, an inhibitor prevents premature polymerization.
Initiator—a chemical that overcomes an inhibitor and allows a reaction to proceed; if it contaminates a monomer outside of a controlled scientific environment, runaway polymerization could occur.
Monomer—a “tiny” molecule that has the unique chemical property of being able to react with itself to form a polymer.
Polymer—a “giant” molecule made up of thousands of monomer molecules that have reacted with themselves in a special type of chemical reaction called polymerization.
Polymerization—a unique chemical reaction in which a monomer (a very tiny reactive molecule) reacts with itself to form a “giant” molecule called a polymer.
Radical—a molecular fragment that, when attached to another molecular fragment or hydrocarbon backbone, will impart specific properties to the new compound.
Reactor—a pressurized vessel used to carry out certain chemical reactions, especially polymerization.
Volatilize—to cause to be evaporated.
