Dust Exposure Control and Mitigation Procedures

This document outlines critical safety procedures for controlling and mitigating dust exposure hazards in the workplace. It includes information on permissible exposure limits (PELs), required respiratory protection, and engineering controls for dust suppression to ensure a safe and healthy working environment.

Permissible Exposure Limits (PELs)

The employer shall ensure that no employee is exposed to an airborne concentration of respirable crystalline silica in excess of 50 µg/m³, calculated as an 8-hour Time-Weighted Average (TWA). [2]

Exposure Assessment

General:

The employer shall 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. This assessment can be performed using either the performance option or the scheduled monitoring option. [2]

Performance Option:

The employer shall assess the 8-hour TWA exposure for each employee based on a combination of air monitoring data or objective data sufficient to accurately characterize employee exposures to respirable crystalline silica. [2]

Scheduled Monitoring Option:

The employer shall perform initial monitoring to assess the 8-hour TWA exposure for each employee. This assessment should be based on 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 can be used where several employees perform the same tasks on the same shift and in the same work area; in such cases, the employer may sample a representative fraction of these employees, focusing on those expected to have the highest exposure to respirable crystalline silica. [2] [3]

If initial monitoring indicates that employee exposures are below the action level, the employer may discontinue monitoring for those employees. If exposures are at or above the action level but at or below the PEL, monitoring must be repeated within six months. If exposures are above the PEL, monitoring must be repeated within three months. If subsequent monitoring shows exposures below the action level, monitoring must be repeated within six months until two consecutive measurements, taken seven or more days apart, are below the action level. [3] [3] [3] [3]

Exposure reassessment is required whenever changes in production, processes, 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 there is any reason to believe that such exposures have occurred. [3]

Respiratory Protection

Where feasible engineering controls and work practices are not sufficient to reduce employee exposure to or below the PELs, the employer shall use them to reduce employee exposure to the lowest levels achievable by these controls and shall supplement them by the use of respiratory protective devices. [1]

For workers engaged in spray application methods, respiratory protection must be used in addition to feasible engineering controls and work practices to reduce employee exposure to or below the PELs. [1]

Respirators used for abrasive-blasting operations must be approved by NIOSH under 42 CFR part 84. Abrasive-blasting respirators shall be worn by all abrasive-blasting operators when working inside blast-cleaning rooms, when using silica sand in manual blasting operations where the nozzle and blast are not physically separated from the operator in an exhaust ventilated enclosure, or where concentrations of toxic dust dispersed by the abrasive blasting may exceed the limits set in 1926.55 or other pertinent sections of this part and the nozzle and blast are not physically separated from the operator in an exhaust-ventilated enclosure. [11] [11]

Properly fitted particulate-filter respirators, commonly referred to as dust-filter respirators, may be used for short, intermittent, or occasional dust exposures such as cleanup, dumping of dust collectors, or unloading shipments of sand at a receiving point when it is not feasible to control the dust by enclosure, exhaust ventilation, or other means. The respirators used must be approved by NIOSH under 42 CFR part 84 for protection against the specific type of dust encountered. [11]

A respiratory protection program as defined and described in 1926.103, shall be established wherever it is necessary to use respiratory protective equipment. [11]

Engineering Controls for Dust Suppression

To control and mitigate dust exposure, employers should implement one or any combination of the following engineering controls:

Local Exhaust Ventilation:

Use local exhaust ventilation equipped with HEPA filter dust collection systems to capture dust at its source. [1]

General Ventilation:

Implement general ventilation systems to dilute and remove airborne dust. [1]

Wet Methods:

Apply water at flow rates sufficient to minimize the release of visible dust when performing tasks using wet methods. [2]

Enclosed Cabs and Booths:

For measures implemented that include an enclosed cab or booth, ensure that the enclosed cab or booth:

Is maintained as free as practicable from settled dust. [2]

Has door seals and closing mechanisms that work properly. [2] [14]

Has gaskets and seals that are in good condition and working properly. [2] [10]

Is under positive pressure maintained through continuous delivery of fresh air. [2] [10]

Has intake air that is filtered through a filter that is 95% efficient in the 0.3-10.0 µm range (e.g., MERV-16 or better). [2] [10]

Has heating and cooling capabilities. [2] [10]

Other Engineering Controls:

Implement other engineering controls such as isolation and enclosure that are feasible. [1]

Work Practices

Utilize appropriate work practices to minimize dust exposure. [1]

Prohibitions

Compressed air shall not be used to remove dust, unless the compressed air is used in conjunction with an enclosed ventilation system designed to capture the dust cloud created by the compressed air. [1]

Employee Rotation

The employer shall not use employee rotation as a means of compliance. [1]

Equipment-Specific Controls

Walk-Behind Milling Machines and Floor Grinders:

Use machines equipped with an integrated water delivery system that continuously feeds water to the cutting surface, and operate and maintain the tool in accordance with the manufacturer's instructions to minimize dust emissions. Alternatively, use a machine equipped with a dust collection system recommended by the manufacturer, ensuring the dust collector provides the air flow recommended by the manufacturer or greater, and has a filter with 99% or greater efficiency and a filter-cleaning mechanism. When used indoors or in an enclosed area, use a HEPA-filtered vacuum to remove loose dust in between passes. [6] [6] [6] [6] [6]

Small Drivable Milling Machines (less than half-lane):

Use a machine equipped with supplemental water sprays designed to suppress dust. Water must be combined with a surfactant, and the machine should be operated and maintained to minimize dust emissions. [6] [6]

Large Drivable Milling Machines (half-lane and larger):

For cuts of any depth on asphalt only, use a machine equipped with exhaust ventilation on the drum enclosure and supplemental water sprays designed to suppress dust. Operate and maintain the machine to minimize dust emissions. For cuts of four inches in depth or less on any substrate, use a machine equipped with exhaust ventilation on the drum enclosure and supplemental water sprays designed to suppress dust, and operate and maintain the machine to minimize dust emissions. Alternatively, use a machine equipped with supplemental water spray designed to suppress dust, ensuring water is combined with a surfactant, and operate and maintain the machine to minimize dust emissions. [9] [9] [9] [9]

Crushing Machines:

Use equipment designed to deliver water spray or mist for dust suppression at the crusher and other points where dust is generated (e.g., hoppers, conveyors, sieves/sizing or vibrating components, and discharge points). Operate and maintain the machine in accordance with the manufacturer's instructions to minimize dust emissions. Use a ventilated booth that provides fresh, climate-controlled air to the operator, or a remote control station. [8] [8] [8]

Heavy Equipment and Utility Vehicles:

For heavy equipment and utility vehicles used to abrade or fracture silica-containing materials (e.g., hoe-ramming, rock ripping) or used during demolition activities involving silica-containing materials, operate the equipment from within an enclosed cab. When employees outside of the cab are engaged in the task, apply water and/or dust suppressants as necessary to minimize dust emissions. For tasks such as grading and excavating (but not including demolishing, abrading, or fracturing silica-containing materials), apply water and/or dust suppressants as necessary to minimize dust emissions. Alternatively, when the equipment operator is the only employee engaged in the task, operate the equipment from within an enclosed cab. [8] [8] [8] [8]

Abrasive Blasting

Substitution of Abrasive Blasting Materials:

Abrasive blasting materials containing crystalline silica shall be replaced with less toxic materials, where practicable. [12]

Cleanup Procedures:

Used abrasive blasting materials which contain a hazardous substance shall be removed from the work area using effective procedures designed to minimize the generation of airborne dust and wearing suitable personal protective equipment. Removal shall take place by the end of each shift unless a risk assessment establishes that the risks from removal exceed the risks from leaving the materials in place, a worker will not be exposed to the materials before removal occurs, or the materials cannot be separated from the environment in which the abrasive blasting takes place. Where removal is delayed, an employer shall assess the risks arising from delay and develop written safe work procedures. [12] [12] [12]

Ventilation

Wherever dry grinding, dry polishing or buffing is performed, and employee exposure, without regard to the use of respirators, exceeds the permissible exposure limits, a local exhaust ventilation system shall be provided and used to maintain employee exposures within the prescribed limits. [7]

Hoods connected to exhaust systems shall be used, and such hoods shall be designed, located, and placed so that the dust or dirt particles shall fall or be projected into the hoods in the direction of the air flow. No wheels, discs, straps, or belts shall be operated in such manner and in such direction as to cause the dust and dirt particles to be thrown into the operator's breathing zone. [7]

Dust shall not be permitted to accumulate on the floor or on ledges outside of an abrasive-blasting enclosure, and dust spills shall be cleaned up promptly. Aisles and walkways shall be kept clear of steel shot or similar abrasive that may create a slipping hazard. [4]

Exhaust Ventilation System

An exhaust ventilation system is a system for removing contaminated air from a space that is comprised of two or more of the following elements:

An enclosure or hood. [5]

Duct work. [5]

Dust-collecting equipment. [5]

Exhauster. [5]

Discharge stack. [5]

General Ventilation Standards

Whenever hazardous substances such as dusts, fumes, mists, vapors, or gases exist or are produced in the course of construction work, their concentrations shall not exceed the limits specified in 1926.55(a). When ventilation is used as an engineering control method, the system shall be installed and operated according to the requirements of this section. [13]

Local exhaust ventilation when used shall be designed to prevent dispersion into the air of dusts, fumes, mists, vapors, and gases in concentrations causing harmful exposure. Such exhaust systems shall be so designed that dusts, fumes, mists, vapors, or gases are not drawn through the work area of employees. [13]

Exhaust fans, jets, ducts, hoods, separators, and all necessary appurtenances, including refuse receptacles, shall be so designed, constructed, maintained and operated as to ensure the required protection by maintaining a volume and velocity of exhaust air sufficient to gather dusts, fumes, vapors, or gases from said equipment or process, and to convey them to suitable points of safe disposal, thereby preventing their dispersion in harmful quantities into the atmosphere where employees work. [13]

The exhaust system shall be in operation continually during all operations which it is designed to serve. If the employee remains in the contaminated zone, the system shall continue to operate after the cessation of said operations, the length of time to depend upon the individual circumstances and effectiveness of the general ventilation system. [13]

The air outlet from every dust separator, and the dusts, fumes, mists, vapors, or gases collected by an exhaust or ventilating system shall discharge to the outside atmosphere. Collecting systems which return air to work area may be used if concentrations which accumulate in the work area air do not result in harmful exposure to employees. Dust and refuse discharged from an exhaust system shall be disposed of in such a manner that it will not result in harmful exposure to employees. [13]

Operational Procedures and General Safety

With respect to operational procedures and general safety, dust shall not be permitted to accumulate on the floor or on ledges outside of an abrasive-blasting enclosure, and dust spills shall be cleaned up promptly. Aisles and walkways shall be kept clear of steel shot or similar abrasive that may create a slipping hazard. [5]

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