Chemical energy 101
Despite the chemically active nature of cement and lime, MSHA reports that there were only 196 chemical burn injuries in stone, sand and gravel from 1998 to 2002. That is an average of 39 per year. In those years, there were no chemical-related fatalities. Out of the 3,334 fatal and nonfatal injuries in the industry in 2002, only 43 were chemical-related. Reported chemical injuries are rare.
Some chemical reactions release energy. Explosives used in blasting generate a good bit of heat (”heat out” or exothermic) and gas when they are set off. The gas expands. The mechanical action of explosive shock and the expanding gas breaks the rock.
In other reactions, heat from an outside source (”heat in” or endothermic) is required to start some chemical reactions and keep them going. In a kitchen experiment, dissolving two Alka-Seltzer tablets lowered about 8 oz. of water 1/2[degrees] Fahrenheit. Heat packs from the drug store, after they are activated, demonstrate an exothermic reaction.
Burning cement clinker or driving off the carbon dioxide in manufacturing lime takes large amounts of fuel for heat. Plant managers spend a lot of time trying to control their fuel costs. Keeping a respectful distance from the kilns and the finished product fresh from the kilns is a foolproof way to avoid thermal burns.
Cement and lime burns
Cement or lime, mixed with water, form bases that are caustic. Cement and lime burns proceed differently than acid burns. The chemical action of cement and lime burns is believed to extract water from inside the contacted cells causing dehydration of the exposed cells.
The compound from cement or lime, dissolved in water, changes the nature of the fats in the skin and the fats can no longer perform their protective function. The solution also forms a compound that speeds up further penetration of the offending chemical into the wound. This damaging action continues until the caustic solution is washed away.
Cement and lime dust, when combined with sweat, can produce this reaction. Continuous clean up throughout the day helps to keep the exposure from cement and lime to a minimum. Keeping the accumulations of dust off sweating skin goes a long way toward preventing cement and lime burns.
The exposure and resulting harm from cement and lime burns can start before symptoms reach the pain stage. Skin can start to redden before there is any pain. It is important to be alert to when and where there can be exposure to cement and lime dust that can collect and will become wet enough to cause a problem. Avoiding the hazard is better than trying to cure a chemical burn injury.
A great deal of the information about cement and lime burns comes from ready-mix concrete experience. Doctors include the abrasions from the mechanical contact with plastic concrete as a complicating factor. There are cases where the “cement water” has penetrated shoes and, after a days work, the injury has made substantial progress before it is recognized.
Doctors also consider the pressure from shoes, or any tight-fitting clothes, as a chemical burn facilitator. The abrasions and pressure are believed to speed up the penetration of the “cement water” into the skin. There are cases where a burned worker has waited 48 hours before seeking medical attention. In these long delay cases, the injury is often a full thickness chemical burn of the skin and skin grafts are required for treatment.
Acid burns
In general, acid burns are less severe than basic or caustic burns. An acid reacting with the skin actually slows the penetration of the acid. The slower and shallower penetration provides more time for treatment. However, acid burns are still serious and need prompt attention.
The first action is to limit the exposure to the offending chemical. Cut the clothes away and start flooding the exposed area with water. It is important to cut the clothing away to avoid contaminating any other part of the victim by pulling the clothes off. The first aid provider should avoid contacting the chemical. Dilution is a solution in this case, and a most important one. The second step is to get medical attention with as complete a description of the exposure and the chemical as possible. The emergency room response is far more effective when the medical professionals are given a heads up on what they are dealing with. Bad information delays a good response.
Safety tip
Keeping the accumulations of dust off sweating skin goes a long way toward preventing cement and lime burns.
Carl R. Metzgar, CSP, has more than 30 years of safety and health experience in the pit and quarry industries. He was formerly a safety and health director for Lone Star Industries, and Mideast Division safety director for Vulcan Materials.