BENZENE

BENZENE

HAZARDOUS MATERIALS

CHEMICAL DATA NOTEBOOK SERIES #29

BENZENE IS A carcinogenic, flammable, toxic, clear, colorless, volatile liquid with a familiar aromatic odor. It’s used as a solvent for rubber and other polymeric materials and replaced tetraethyl lead as an additive in unleaded gasolines. It’s also an intermediate or raw material in the manufacture of detergents, dyes, explosives, pesticides, plastics, and many other chemicals. It was the sixteenth highest chemical in volume produced in the United States in 1985.

Benzene is the simplest of the class of organic chemicals known as “aromatic.” It earned this name when it was first synthesized; the odor was described as being pleasant and aromatic. Among the many chemicals in which it’s used as an intermediate are those that contain the “benzene ring,” among which are toluene and the xylenes, the most common of the solvents made this way. Phenol, or carbolic acid, is another common chemical containing the benzene ring. Explosives such as TNT (trinitrotoluene) and picric acid (trinitrophenol) contain the benzene ring, as well as important chemicals like aniline and styrene.

Benzene became widely used in the rubber industry because of its solvent power, which meant it was a good adhesive wherever rubber had to be bound to itself or some other material. For years, workers literally sloshed the liquid around, applying it to rubber plies to build tires and other manufactured rubber goods. Most often workers did this witH no skin or respiratory protection. No complaints were voiced because benzene smelled so good. However, after years of exposure to benzene, workers became ill with aplastic anemia and leukemia. Today, benzene is a known human carcinogen, and workers must not be exposed to amounts above the Threshold Limit Value— Lime Weighted Average (TLV-TWA).

PROPERTIES

Benzene has a flash point of 12°F, an ignition temperature of 1,044°F, and flammable limits of from 1.3% to 8.0%. It has a specific gravity of 0.88, a molecular weight of 78. and a vapor density of 2.69. It boils at 176.2°F, freezes at -t 1 9°F, and is very slightly soluble in water.

Benzene doesn’t react with water or with many common chemicals. However, it will react with all strong oxidizing agents, including chlorine, oxygen, ozone, perchlorates, permanganates, and peroxides.

HAZARDS

Benzene’s hazards are tied to its molecular structure, which was a mystery for many years. Using certain analytical methods, chemists were able to determine that benzene’s molecular formula was Q,H However. to achieve a molecular structure with this formula, it would be necessary for the structure to contain multiple covalent bonds, which would make benzene very reactive (which it’s not). Experiments using oxidizing agents showed reactivity consistent with such a proposed structure, but benzene doesn’t burn very easily, as it should if it had the suspected structure.

Despite its low flash point, it has a relatively high ignition temperature for a six-carbon hydrocarbon. For example, other six-carbon flammable liquid hydrocarbons, like hexane, whose formula is C-,lli, has an ignition temperature of 500°F, and hexene, formula CH has an ignition temperature of I8*” F. When benzene is ignited, it burns with a very smoky flame and produces tremendous quantities of carbon monoxide, both indicative of a material that’s difficult to burn.

The answer to benzene’s structure is said to have come to a 19th-century chemist during a dream. The only possible solution was a series of alternating double bonds in a cyclical structure such as:

The circle inside the hexagon indicates resonance between two alternating structures. This structure explains the presence of double covalent bonds, yet explains why it’s not as reactive as it should be. There are still carbon atoms at each apex and one hydrogen atom attached to each carbon. They are just not shown.

Benzene’s structure and molecular weight produce two hazards—the low flash point and the enhanced production of carbon monoxide during combustion. Its low flash point means that there will be vapors present within the flammable range at most ambient temperatures. Its vapor density of 2.69 means that the vapors will hang together and flow along low spots in the ground, usually far enough to find an ignition source. The resulting fire will flash back to the source of vapors. Its carcinogenic nature must also be tied to its molecular structure.

The. chemical’s very slight solubility in water and its specific gravity of 0.88 means the liquid will be displaced by water and will float on top of it, while dissolving very, very slowly.

Benzene is very irritating to the skin because it will dissolve fat from the cells. This will produce dry, scaly, reddened skin that’s prime for infection. Benzene may also be absorbed through the skin. Contact with the eyes will produce severe irritation.

Benzene is a central nervous system depressant. High concentrations in air will produce headache, dizziness, euphoria, nausea, convulsions, and coma. Death may be caused by ventricular fibrillation.

Ingestion of benzene liquid will produce irritation of the gastrointestinal tract. Aspiration could cause pulmonary edema, which may not occur until some time after the exposure.

The TLV-TWA for benzene is 10 parts per million, and the STEL (Short Term Exposure Limit) for 15 minutes is 25 ppm. These values are now under review and could be lowered in the near future. The odor of benzene can be detected by some people at levels below 0.25 ppm, but is more likely to be detected at levels near 2 ppm. Concentrations of 2% (20,000 ppm) could produce death in 5 to 10 minutes.

NON-FIRE RELEASES

In the event of a spill of benzene, and no fire has yet occurred, take all precautions normally associated with flammable liquids. Approach from upwind, eliminate all ignition sources, and contain the material.

Evacuation is always a prime consideration, particularly downwind. The vapors of benzene will travel a great distance because of the chemical’s vapor density. These vapors produce an explosion hazard as well as a health hazard. Just because a liquid is called “flammable” and a flash point, ignition temperature, and flammable limits are given, emergency responders believe that an ignition source will produce only a fire. They’re partly right. What happens first when an ignition source of sufficient energy (producing temperatures at or above the ignition temperature of the flammable liquid) contacts the vapors of a flammable liquid within the flammable range is an explosion! After the explosion comes the fire. Often the explosion is much more devastating than the fire, causing more deaths, injuries, and property damage.

SYNONYMS

annulene

(6) annulene

benzol

benzole

bicarburet of hydrogen

carbon oil

coal naphtha

cyclohexatriene

mineral naphtha

motoe benzol

nitration benzene

phene

phenyl hydride

pyrobenzol

pyrobenzole

benzin (obsolete)

benzine (obsolete)

NCI-c55276

RCRA Waste Number U019

IDENTIFICATION NUMBERS AND RATINGS

UN/NA

(United Nations/North America)

1114

CAS

(Chemical Abstract Service)

71-43-2

RTECS

(Registry of Toxic Effects of Chemical Substances) CY1400000

CHRIS

(Chemical Hazard Response Information System) BNZ

STCC

(Standard Transportation Commodity Code)

4908110

NFPA 704 rating

(National Fire Protection Association)

2-3-0

IMO

(International Maritime Organization)

3 2, flammable liquid

If the container is leaking liquid, efforts can be made to try to catch the liquid in a secure container. If no secure container is available or large enough, efforts can be made to catch the liquid in a temporary container and simultaneously pump it back into the leaking container (assuming a tanker of some sort is involved), thus creating a semi-closed system. Care must be taken to use explosion-proof pumping equipment if attempting this technique. The system will not be closed and escaping flammable vapors may ignite.

If possible, contain the liquid by building a containment pond, using soil, sand, clay, or other absorbent materials. A containment pit can also be used, if equipment is available to dig it. Pits are usually better than ponds, because the surface area of a pit is usually less than that of a pond. Less surface area means slower evaporation, which means less vapors are produced. Also, a pit is easier to cover with foam or compatible material. If containment ponds or pits are built using earthmoving equipment or trenches are dug to lead the liquid to the containment area, care must be taken to use non-sparking tools and equipment to prevent an explosion.

Once the liquid is contained, it may be pumped or vacuumed into secure containers. Any remaining liquid may be absorbed by using straw, hay, peat, clay, fly ash, cement powder, or any commercial sorbent. Once the last liquid is removed, the contaminated soil will have to be removed. A drawback of the containment pit is that soil contamination is usually more extensive, and the soil is more difficult to remove. All contaminated soil and sorbents must be disposed of in accordance with federal, state, and local regulations and should be done by professionals under the direction of the proper environmental authorities.

All catch basins, sewer openings, and other entryways to streams or waterways must be diked to prevent entry of benzene. If the liquid does reach a waterway, it will float on top of the water and can be skimmed off using oil-skimming booms. Straw, hay, or peat moss will help absorb the liquid as it slows near the boom. Once benzene reaches a waterway, all downstream users must be notified immediately, regardless of attempts to remove it. Intake of water contaminated by benzene into an industrial operation could cause an explosion. Contaminated water should be diverted into a holding pond until the benzene can be removed.

Ihe proper environmental authorities should direct disposal techniques. Salvage and clean-up procedures should be carried out by well-trained, qualified professionals who are properly equipped to do the job. Local emergency response personnel shouldn’t be involved in salvage and cleanup.

FIRE SCENARIO

If containers of benzene are exposed to flames or to the radiated heat of a nearby fire, evacuation should be carried out for a radius of 3,000 feet for very large containers such as tankers and tank wagons, 300 feet tor drums and smaller containers. Efforts to cool the containers may be carried out if the exposure to heat hasn’t been long Water should be applied from as great a distance as possible, and. in the case of large containers, unmanned appliances should be used. Benzene is a volatile liquid. Tremendous amounts of vapor will be produced as the liquid is heated, creating a dangerous buildup of pressure within any container. Such a buildup w ill produce a catastrophic disintegration if the pressure isn’t safely relieved. If such a release occurs, an explosion resembling a BLEVE (which technically occurs only with easily liquifiablc flammable gases) will occur.

If the container of benzene is being heated. and it has a safety relief device—such as a spring-loaded valve —functioning properly, the vapors will le expelled through the safety relief valve. These vapors, of course, are highly flammable, and only a suitable ignition source is needed to ignite them. This can occur explosively if the ignition source is some distance from the source of vapors.

If the released vapors are burning, they shouldn’t be extinguished unless their flowcan be stopped immediately. If the flame is extinguished, an explosive collection of vapors could collect. Intentional reignition of the vapors is a technique that can be used safely if done immediately. This technique is highly dangerous and could produce the violent explosion that emergency responders are trying to eliminate.

If a pool of the released liquid is burning, extinguishment techniques must be carried out while firefighters are wearing positivepressure self-contained breathing apparatus. This is true even fighting the fire from upwind while outside, because of the tremendous generation of carbon monoxide byburning benzene.

GLOSSARY

BLEVE—An acronym for boiling liquid, expanding-vapor explosion.

Carcinogen—A substance that causes cancer.

Covalent bond—The sharing of two electrons between two atoms.

Hydrocarbon—A covalent compound containing only carbon and hydrogen in the molecule.

Ignition temperature —The minimum temperature to which a material must be raised before it will ignite.

Organic—Pertaining to organic chemistry, which is the chemistry’ of compounds which were part of living things. Generally recognized as the chemistry of hydrocarbon compounds and their derivatives.

Resonance—A molecular structure that’s fluctuating (resonating) back and forth between alternate forms. A theory used to explain molecular structure that can’t be explained by the rules of covalent lnding.

Specific gravity—The weight of a solid or liquid as compared to the weight of an equal volume of w ater.

Vapor density—The relative density of a vapor or gas as compared to air.

Benzene can be extinguished by the use of water fog or high-pressure water spray, foam, dry’ chemical, or carbon dioxide, depending on the amount spilled, the surface area of the burning liquid, wind and weather conditions, and resources available. Training procedures used for other flammable liquids with low flash points may be sufficient to handle benzene, if one remembers its toxicity hazard and the production of large amounts of carbon monoxide.

PROTECTIVE CLOTHING

Any clothing selected must prevent benzene from contacting the skin or eyes, and must keep vapor from the same contacts and from the respiratory system. This means impervious gloves, boots, face shields and goggles in addition to impervious clothing. The manufacturers of benzene should be consulted to determine the proper material. Some manufacturers of protective clothing claim that polyvinyl alcohol and Viton are two impervious materials. Rubber may provide short-term protection, but remember that benzene will dissolve most rubber compounds.

Positive-pressure SCBA should be used to protect the respiratorysystem.

FIRST AID

For inhalation, the victim must be removed to fresh air. If the victim has stopped breathing, or breathing has become difficult, artificial respiration must be administered (mouth-to-mouth resuscitation may expose the provider of first aid to the material in the victim’s mouth or vomit). Medical attention must be provided immediately.

For skin contact, all contaminated clothing should be removed and all affected bodyareas washed with large amounts of water. Medical attention is necessary if irritation of the skin persists after washing.

For eye contact, the eyes should be flushed immediately w-ith large amounts of water for 15 minutes, occasionally lifting the eyelids. Get medical attention.

For ingestion, don’t make the victim vomit. Keep the victim warm and get immediate medical attention.

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