Health and Safety in Heavy Industries
Health and Safety in heavy Industries – Many vapours and gases found in heavy industries pose an explosion risk.
For any gas to combust, it must reach its lower explosive limit (LELs). Lower explosive limits have been well established for 100s of chemicals and generally vapours from VOCs have relatively low explosion limits. For example, methane and hydrogen have LELs of 50,000 ppm and 40,000 ppm respectively whereas benzene has an LEL of only 13,000 ppm.
At high concentrations VOC are also an asphyxiation risk. Like CO2, a gas all too frequently responsible for serious effects on human health, VOC are much denser than air. Therefore, where confined spaces exist it is possible for VOCs to displace oxygen and create dangerous environments. The most common threats to workers from VOCs are their multiple toxic effects. The effects we are most familiar with are the acute risks, such as, eye, nose and throat irritation, dizziness and at high concentrations unconsciousness and even death. However, the potentially larger threat comes from low-level, long-term exposures we are not aware of. These include kidney damage, immunological effects, central nervous system damage, increased leukaemia and other cancer rates. Using benzene, as an example, this can be powerfully illustrated.
Benzene evaporates easily and can be detected by the human nose at approximately 3 ppm. The table below indicates that physical symptoms of benzene exposure occur much higher than this – our nose would give us warning before we came to harm. However, the effects of long term, low level exposure to concentrations below what our nose can detect have been extensively documented and are known to increase cancer rates.
To protect workers from dangerous exposure to VOCs, occupational exposure limits (OELs) have been put in place. OELs are the maximum concentration an unprotected worker can be exposed to in the workplace. OELs are divided in to two categories i) Time Weighted Average (TWA) calculated over an 8 hour exposure ii) Short Term Exposure Limit (STEL) the maximum exposure over 15 minutes.
OELs for benzene across Europe and the USA are in the table below. The limits for benzene are typically below 1 ppm, well below what we can smell. OELs for hundreds of VOCs have been set and range from 100s of ppm to sub ppm levels.
It is estimated that occupational cancers are a leading cause of work related death worldwide. According to a study in Great Britain over one year, 5% of cancer deaths (8000) were attributable to occupational exposure.
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