Silicosis is a preventable occupational disease

Workplace exposure to crystalline-free silica can be controlled by several possible means, which may be included in a control program. The control program is the product of the workplace assessment of exposure. Several possible strategies may be used depending on the effectiveness of existing facilities and practices. Usually, a combination of controls is most suitable.

A control program is necessary where the assessment shows that “a worker is likely to inhale silica and that the health of a worker may be affected.” Note that in this context no reference is made to numerical values. The joint health and safety committee must also be consulted on the control program, which should include provisions for the following:

ENGINEERING CONTROLS

Engineering controls are most effective in workplaces in which the production of dust is presently uncontrolled. These often produce the most dramatic results when used properly and installed correctly. Engineering controls are selected to control emissions at their source. These may include any or all of the following:

Hazardous-Liquid-Wastes
  • Process Selection/Workplace Design

Process selection and layout can significantly affect the production of silica-containing dust. Attention to the mechanics of silica handling can lead to the selection of processes least likely to generate dust, and of workplace layouts that minimize the spread of dust. These considerations are best addressed during the design stages.
Mechanization often offers the advantage of increased production and improved protection of workers.

  • Equipment Selection

The ideal time to address engineering controls is during the selection of new or replacement equipment. Equipment selected for silica handling or in which silica-containing dust is generated, should enclose the process and contain venting points capable of being connected to local exhaust ventilation. Manufacturers’ specifications should be examined to ensure that these capabilities are included. Performance specifications with an expected warranty should be proposed by the purchaser and submitted as part of the purchasing requirement. Ensuring that the specifications are met at the time of start-up is essential to future performance and maintenance.

  • Modification of Existing Equipment or Processes

Control of silica in the workplace can sometimes be achieved by modifying existing processes or equipment. Less hazardous materials can sometimes be substituted for silica. This change should be examined carefully to ensure that product quality remains high and that other problems are not introduced.

The use of silica may be eliminated from the process when alternate technologies become available. Once again, the alternative should be examined to ensure that it meets the need at hand and does not introduce new hazards.

The most common modification of existing processes is isolation. Sources of silica dust can sometimes be isolated from workplace air by enclosing the equipment or by separating it from workers by barriers or walls. Sometimes special booths may be used to isolate the worker from the source of silica dust.

  • Ventilation

Ventilation of the workplace is essential to maintaining acceptable conditions of exposure. Workplace ventilation may be provided in two ways: natural or mechanical ventilation. Natural ventilation relies on the principle that heated air expands and rises. Natural airflow in a building can be obtained by providing openings at floor level and roof level. This type of ventilation is most effective when the openings are as far apart vertically as possible and the inlet and outlet areas are equal.

Mechanical ventilation is provided by fans. This may be required when natural ventilation is inadequate. Exhaust fans located at the roof level may supplement natural ventilation in controlling dust generated by process emissions.

More effective mechanical ventilation is provided by local exhaust systems. The collecting hood should be located as close as possible to the source of emission. The air velocity measured at the opening of the hood, the capture velocity, must be sufficient to collect the dust.

Generally, the face velocity must be at least 60 m/min (220 ft/min). Local exhaust ventilation is usually required when existing equipment is enclosed. Air containing silica dust should be passed through a dust collector before being drawn through the fan. Waste air should be exhausted through a stack to the outdoors.

Exhausted air must comply with environmental emission standards. In all cases in which mechanical exhaust ventilation is installed, make-up air must be provided. Make-up air is required to maintain the air balance within the building. Suction fans will be “starved” if not provided with sufficient make-up air.