Benzene--The Next Asbestos? Monitor in g technologies to mitigate r isk and cr ea t e a safer and mor e compliant plant envir on m en t By Meg Godfrey, RAE Systems A graduate in mechanical engineering from the University of Texas at Austin, Meg Godfrey is the Product Marketing Manager for Portable Products for RAE Systems, Inc., (www.raesystems.com) of San Jose, California. She can be reached at [email protected]. The thr ea t of benzene The aromatic hydrocarbon benzene is almost everywhere. It is a component of gasoline, and it is an important industrial solvent and precursor in the production of drugs, plastics, synthetic rubber, and dyes. It is a natural constituent of crude oil, but it is usually synthesized from other compounds present in petroleum. It is found in high concentrations in cigarette smoke. Like asbestos, the use and handling of benzene has changed over the past several decades as its toxic properties have become better understood. As the understanding of the threat has developed, various sensing technologies and regulations have been used to provide better protection of people at higher risk of exposure. Histor y and uses Benzene was first discovered and isolated from coal tar in the 19th century. Prior to the 1920's, benzene was frequently used as an industrial solvent, especially for degreasing metal. As its toxicity became obvious, other solvents replaced benzene in applications that directly exposed the user to benzene. Today, benzene is made mostly from petroleum sources and ranks in the top 20 in production volume for chemicals produced in the United States. By far the largest use of benzene is an intermediate to make other chemicals. The most widely produced derivatives of benzene are styrene, which is used to make polymers and plastics, phenol for resins and adhesives (via cumene), and cyclohexane, which is used to manufacture Nylon. Smaller amounts of benzene are used to make some types of rubbers, lubricants, dyes, detergents, drugs, explosives and pesticides. As many as 238,000 people may be occupationally exposed to benzene in the United States. These industries include benzene production (petrochemicals, petroleum refining, and coke and coal chemical manufacturing), rubber tire manufacturing, and storage or transport of benzene and petroleum products containing benzene. Other workers who may be exposed to benzene due to their occupations include steel workers, printers, rubber workers, shoe makers, laboratory technicians, and gas station employees. Char a ct er ist ics and health effects Benzene is a colorless liquid with a sweet odor. Benzene evaporates into air very quickly, dissolves slightly in water, and is highly flammable. Most people can begin to smell benzene in air at 1.5 - 4.7 parts of benzene per million parts of air (ppm) and can begin to taste benzene in water at 0.5 - 4.5 ppm. Benzene's health hazards are well documented. It is a recognized carcinogen, developmental and reproductive toxicant. It is also suspected as a toxicant in cardiovascular, endocrine, gastrointestinal, immunological, neurological, and respiratory systems.

Short-term exposure to high doses (700 - 3,000 ppm) of benzene may cause drowsiness, dizziness, headaches, tremors, confusion, and/or unconsciousness. Death may occur after oral ingestion or inhalation of very high concentrations (approximately 10,000 - 20,000 ppm) of benzene. People who breathe benzene for long periods may experience harmful effects in the tissues that form blood cells, especially the bone marrow. These effects can disrupt normal blood production and cause a decrease in important blood components. A decrease in red blood cells can lead to anemia. Reduction in other components...

By contrast, gasoline as a whole has an ACGIH TWA of 300 ppm. Therefore, the toxicity of gasoline is controlled mostly by the benzene content. Figure 1 shows that above 0.2% benzene, the TWA of gasoline is dominated by the benzene content rather than the hundreds of other compounds present. Various commercial gasolines contain benzene typically in the range 0.1 2%. Therefore it is critical to measure the benzene concentration directly rather than total hydrocarbons. Many broadband monitoring techniques such as flame ionization detectors (FIDs) or photoionization detectors (PIDs) would give the...

Moreover, LEL sensors are broadband monitors and cannot measure benzene specifically in gasoline mixtures. Types of technologies available for benzene and other har m fu l VOC monitor in g Given that there are multiple technologies available for benzene detection, what is the most appropriate method for protecting the long-term health and safety of workers? Each type of sensing technology has its particular uses, strengths and weaknesses, but PID, or photoionization detection, is frequently the optimal choice for real-time monitoring where benzene is present. There are a number of other technologies...

requiring hours to several days before results are available. During a plant turnaround, every minute of shut-down time is critical and much more rapid feedback is needed to make personal protective equipment decisions for workers. Por t a b le GC Systems. Portable gas chromatographs, usually with PID or FID detectors, provide selective benzene measurements down to 0.1 ppm, but have several drawbacks. They tend to be heavy and bulky, making them difficult to use in tight spaces and on ladders and catwalks. They tend to be relatively expensive and complex; therefore usually only the company industrial...