Silica dust: A deadly possibility for construction workers

By DON LOFGREN
Industrial Hygienist, Washington Department of Labor and Industries

Dust stirred up from concrete work could put workers at risk of the deadly lung disease silicosis.

The grinding, cutting, drilling, abrasive blasting, or other dusty work on concrete, concrete block, or mortar can release a fine dust that may contain crystalline silica. Breathing too much dust can cause a disease for which no cure exists.

Concrete and concrete blocks contain sand and gravel, both of which contain crystalline silica, also known as "free" silica or quartz. Gravel will have varying percentages of the mineral quartz, depending upon where the gravel was obtained. Mortar can also contain sand with crystalline silica. The use of power equipment on these construction materials can soon create a cloud of dust containing fine particles of silica.

The risk of contracting silicosis depends on how much of the dust gets into the air, and how often and for how long a worker is exposed. The illness usually results after perhaps 10 to 40 years of exposure. Fine silica particles find their way into the lungs and damage delicate tissues. Infrequent exposure to low levels of concrete dust likely poses little risk, and most workers exposed to low levels will not be noticeably affected.

But the disease can result even sooner. High dust levels, such as those caused by sandblasting or even dry grinding and cutting in poorly ventilated areas, can cause lung damage after less than a few years of such intense exposure.

The disease from excessive exposure is ugly.

Silicosis turns once-good lung tissue into non-breathing and useless scar tissue. Those afflicted with silicosis first feel a dry cough that can get progressively worse. Shortness of breath follows, at first only with exercise. Breathlessness may occur even when performing routine movements.

Advanced stages of the disease result in death from a person's inability to breathe or just plain failure of the heart due to that organ's attempt to compensate for the damaged lungs.

Silicosis is an old disease that is still being diagnosed. Thousands have already died from exposure to silica in foundries, quarries, mines and from construction activities. More recently, cancer has been associated with silica exposure.

Those afflicted with silicosis, even those without any clear symptoms, are more prone to lung infection. Many die from infections, such as tuberculosis, without even knowing they had silicosis.

State and federal standards determine the amount of silica dust that a worker may be exposed to in a typical eight-hour work shift. The limit is described as a maximum concentration of dust in the air - 0.1 milligrams of respirable crystalline silica per cubic meter of air - that a worker may breathe on average in the eight-hour shift.

You can't see pure crystalline silica dust at the safe exposure level. But if you see a cloud of concrete dust, it is more than likely it contains enough silica to be above the safe level.

The limit places a duty upon an employer to control exposure to silica so that no employee may be exposed above this level. Maintaining safe levels of exposure takes effort.

The best way - and required to be tried first by state worker safety and health rules - is to use dust-control methods, such as water or exhaust ventilation. These are called "engineering controls." It's usually cheaper in the long term than the annual costs of a respirator program, considering the expense of both time and equipment.

As an alternative to water, tools can be ventilated. Grinders and drills can be bought or retrofitted with hoods that when hooked up to an exhaust fan or vacuum with sufficient pull can extract the dust where it is produced. Masonry saws can be bought or adapted with a ventilation hood and air cleaner. The hood is vented so that dust is captured and drawn into a portable air cleaner and away from the operator.

Exhaust ventilation equipment is also sold for concrete cutting, scabbling, slab grinding, leveling and planing. The exhaust should be directed to an air cleaner equipped with an effective filter. A HEPA ((high efficiency particulate arrestance) filter preceded by a pre-filter is best.

Whatever system is tried, air monitoring should be conducted to ensure that exposure levels are below the state limit before a worker removes the respirator.

Work practices at times can be effective, but may not be as reliable. Positioning of the operator or saw may help with reducing the exposure. Moving an operation outdoors or away from walls, or positioning operators so that they are not downwind, can reduce the exposure. But in many cases, re-positioning will not be possible or effective and should not be relied upon.

The use of respirators requires a complete respirator program that includes proper selection, fit tests, medical evaluations, maintenance, training and written guidelines. A "fit test" is needed to select a size and model respirator that will seal on the user's face.

The proper type of respirator is one approved by the National Institute for Occupational Safety and Health, or NIOSH. Look for "NIOSH Approved" on the box or in the instructions. A half-face-type respirator equipped with a HEPA or P-100 filter can be used for low levels of dust - less than 10 times the allowed exposure limit. Higher dust levels require air-supplied respirators.

State law also requires hazard communication for workers who might be exposed to crystalline silica dust. Those exposed to such dust must be provided the following minimal information:

• How and when they may be exposed to silica dusts.
• Possible health hazards of the dust.
• Methods used to control the dust, such as water, ventilation or a protective respirator.
• An explanation of the hazard communication program, including any pertinent labels and material safety data sheets. The data sheets are usually obtained from the manufacturers or distributors of the products.

More help is also available by contacting state Department of Labor and Industries' free consultation service. Individual employers or groups may call (800) 423-7233 and ask for the nearest industrial safety and health consultant.

Silicosis is a deadly disease, but employers and workers can take steps to prevent unnecessary pain and suffering.

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