Under OSHA’s silica dust rule, for tasks not discussed in the previous module, or where the employer does not fully and properly implement the engineering controls, work practices, and respiratory protection as listed, the employer should use the below alternative exposure control methods.
The employer should make sure no employee is exposed to an airborne concentration of respirable crystalline silica in excess of 50 micro grams per cubic meter (μg/m3), calculated as an 8-hour Time Weighted Average (TWA). In other words, the average exposure to silica dust should not exceed 50 ug/m3 during the full work shift.
The employer should assess the exposure of each employee who is or may reasonably be expected to be exposed to respirable crystalline silica at or above the action level of 25 micrograms per cubic meter (μg/m3) using one of the following two methods:
Wherever engineering and work practice controls are not sufficient to reduce employee exposure to or below the PEL, the employer should:
The employer should comply with other OSHA standards, such as 29 CFR 1926.57 Ventilation, where abrasive blasting is conducted.
Assigned Protection Factor (APF) means the workplace level of respiratory protection that a respirator or class of respirators is expected to provide to employees when the employer implements a continuing, effective respiratory protection program. When required by OSHA for reducing exposure to silica dust using the above equipment discussed in this module, using respiratory protection with an APF of 10 is required.
Maximum Use Concentration (MUC) means the maximum atmospheric concentration of a hazardous substance from which an employee can be expected to be protected when wearing a respirator. The MUC is determined by the assigned protection factor of the respirator or class of respirators and the exposure limit of the hazardous substance.
The MUC for respirators is calculated by multiplying the APF for the respirator by the PEL. The MUC is the upper limit at which the class of respirator is expected to provide protection. Whenever the exposures approach the MUC, then the employer should select the next higher class of respirators for the employees.
For more information on APFs and MUCs, refer to OSHA Publication 3352-02, Assigned Protection Factors(pdf).
When using wet methods with electrical equipment of any kind, be sure to use ground-fault circuit interrupters (GFCIs) and watertight, sealable electrical connectors. These features are particularly important to employee safety in wet or damp areas, such as where water is used to control dust.
Although an assured equipment grounding conductor program is an acceptable alternative to GFCIs, OSHA recommends employers use GFCIs where possible because they afford better protection for employees.
Click on the link for more information on OSHA’s Ground-Fault Protection on Construction Site page.
Freezing temperatures complicate the use of water. Consider heating the local work area, if practical, to prevent ice from forming in the water-feed system.
Drain the system when not in use. Large portable heating units are commonly used to heat commercial and sometimes road and highway projects.
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