Alternative Exposure Control Methods
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.
Permissible Exposure Limit (PEL)
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.
Employers who do not fully implement the control methods on Table 1 must:
- Determine the amount of silica that workers are exposed to if it is, or may reasonably be expected to be, at or above the action level of 25 μg/m3 (micrograms of silica per cubic meter of air), averaged over an 8-hour day;
- Protect workers from respirable crystalline silica exposures above the PEL of 50 μg/m3, averaged over an 8-hour day;
- Use dust controls and safer work methods to protect workers from silica exposures above the PEL; and
- Provide respirators to workers when dust controls and safer work methods cannot limit exposures to the PEL.
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:
- Performance Option: The employer should assess the 8-hour TWA exposure for each employee on the basis of any combination of air monitoring data or objective data sufficient to accurately characterize employee exposures to respirable crystalline silica, or
- Scheduled Monitoring Option: The employer should perform initial monitoring to assess the 8-hour TWA exposure for each employee on the basis of one or more personal breathing zone air samples that reflect the exposures of employees on each shift, for each job classification, in each work area.
- Representative Sampling: Where several employees perform the same tasks on the same shift and in the same work area, sample a representative fraction of the employees.
- Sample the employee(s) who are expected to have the highest exposure to respirable crystalline silica.
- If employee exposures are below the action level, discontinue monitoring for those employees.
- If employee exposures are at or above the action level but at or below the PEL, repeat monitoring within six months of the most recent monitoring.
- If employee exposures are above the PEL, repeat monitoring within three months of the most recent monitoring.
- If the most recent (non-initial) monitoring shows employee exposures are below the action level, the employer should repeat the monitoring within six months until two consecutive measurements, taken seven or more days apart, are below the action level. At this time, the employer may discontinue monitoring for those employees unless reassessment is required.
- Reassessment of Exposures: The employer should reassess exposures whenever the following happen:
- a change in the production, process, control equipment, personnel, or work practices may reasonably be expected to result in new or additional exposures at or above the action level, or
- when the employer has any reason to believe that new or additional exposures at or above the action level have occurred.
- Methods of sample analysis: The employer should ensure all samples are taken to satisfy the monitoring requirements discussed above. Samples must be evaluated by a laboratory meeting the requirements of 1926.1153, Appendix A.
- Employee notification of assessment results: Within five working days after completing an exposure assessment, individually notify each affected employee of the results.
- Written notification can be given to each employee or posted in an appropriate location accessible to all affected employees.
- If exposure is above the PEL, the employer should describe the corrective action being taken to reduce employee exposure to or below the PEL.
- Observation of Monitoring: Where air monitoring is performed, the employer should give affected employees or their designated representatives an opportunity to observe any monitoring. When observation of monitoring requires entry into an area where the use of protective clothing or equipment is required:
- the employer should provide the observer with protective clothing and equipment at no cost, and
- make sure the observer uses such clothing and equipment.
- Methods of compliance: The employer should use engineering and work practice controls to reduce and maintain employee exposure to respirable crystalline silica to or below the PEL, unless the employer can demonstrate such controls are not feasible.
Wherever engineering and work practice controls are not sufficient to reduce employee exposure to or below the PEL, the employer should:
- still use them to reduce employee exposure to the lowest feasible level, and
- supplement them with approved respiratory protection.
The employer should comply with other OSHA standards, such as
29 CFR 1926.57 Ventilation, where abrasive blasting is conducted.
Respiratory Protection and Assigned Protection Factor (APF)
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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