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Sulfuric Acid Mist
Judged Cancer Agent

UE News, December 1998

Recently the International Agency for Research into Cancer (IARC), a respected international science group based in Europe, classified sulfuric acid mists as causing cancer in humans. Specifically, the IARC concluded, "There is sufficient evidence that occupational exposure to strong inorganic acid mists containing sulfuric acid is carcinogenic." Also, the American Conference of Government Industrial Hygienists (ACGIH) has for several years listed sulfuric acid mists as a "suspected human carcinogen."

These conclusions are based on worker health studies in a number of industries involving exposure to sulfuric acid mists. Thus workers in fertilizer plants, steel pickling plants and chemical and soap manufacturing have shown increases in lung, nasal and larynx cancers. An acid mist is a suspension of acid droplets in air. (Skin or eye contact with sulfuric acid, while dangerous in their own right, do not appear to cause increased rates of cancer.)


This new classification of sulfuric acid mist as cancer causing is of special concern because sulfuric acid is one of the most commonly used industrial chemicals. In the U.S. alone, more than 40 million tons of sulfuric acid are manufactured and used each year. The National Institute for Occupational Safety and Health (NIOSH) estimates that more than 200,000 U.S. workers are regularly exposed to sulfuric acid.

Sulfuric acid baths are used in electroplating, as well as metal cleaning, etching and pickling processes. Sulfuric acid is widely used in car and truck storage batteries, and thus workers who manufacture, recycle or recharge batteries may be exposed to hazardous acid mists. Also, sulfuric acid is used in the production of phosphate fertilizers, in pulp mills and paper manufacturing and in the production of textile fibers.

The OSHA legal limit for sulfuric acid exposure is 1 milligram of sulfuric acid per cubic meter of air (1 mg/m3). Also, ACGIH further recommends a 3 mg/m3 short-term exposure limit during any 15-minute work period.

The main health effects of short-term exposure to sulfuric acid vapors and mists are irritation and burning of the skin and the moist tissues of the eyes, nose and throat. Breathing in acid vapors and mists can cause chest tightness and shortness of breath. If the exposure continues, the burning and irritation of the lining of the lungs can cause fluids to collect in the lungs, which can lead to pneumonia, respiratory failure and death. Until recently, it was not recognized that heavy exposure to sulfuric acid mists could also lead to respiratory system cancers. The finding is of special concern to workers who smoke cigarettes, since they are already at elevated risk of lung cancer.

It should also be noted that the OSHA sulfuric acid standard was adopted long before this acid was suspected as a cancer agent. Since there are currently no known safe levels of exposure to cancer agents, union health and safety committees should work to prevent all unnecessary sulfuric acid mist exposure. We should be guided by the ALARA Principle, used to protect nuclear industry workers: Seek exposure levels As Low As Reasonably Achievable.


The most important single factor in reducing sulfuric acid mist is to make sure that all acid tanks and acid processes are properly ventilated. For open tanks, as in electroplating, so-called push-pull ventilation is recommended, which pulls mists away from workers’ breathing zones. Also, many battery recharging areas within plants are poorly ventilated. In this process, when explosive hydrogen gas is released, it bubbles up in the acid bath and lots of sulfuric acid mist may be generated. Based on our new cancer information, these battery-charging areas need to be very well ventilated, which will prevent both hydrogen gas and sulfuric acid mist buildup.

In general, if you or others are experiencing eye and throat irritation near sulfuric acid processes, consider this an early warning sign of possible sulfuric acid overexposure. In this case ask management through your union officers or health and safety committee to measure the level of sulfuric acid in the workroom air. And remember, if the level is below the OSHA limit of 1 mg/m3, this may get OSHA off your employer’s back (for the moment), but this is no longer adequate protection for you or your union sisters and brothers. Remind your employer that sulfuric acid mist is now considered a human cancer agent, and that it is necessary to reduce the level of exposure to be as low as reasonably possible. And no, respirators are not the answer to this problem — they leak, they are uncomfortable and they don’t protect people who work nearby or pass through the hazard area on occasion. Proper, well-maintained exhaust ventilation is what is needed to reduce hazards for all in the shop.

Also, it is important to check the sulfuric acid Material Safety Data Sheets (MSDSs) in your plant to make sure that they are up-to-date and reflect this cancer information. If they don’t, this needs to be brought to the attention of management, and they need to request new, updated MSDSs from their suppliers. Furthermore, any hazard communication training in the future needs to reflect this new understanding of sulfuric acid hazards.

And finally, since this is December, have a safe and happy holiday season!

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