Safety in Design - Engineering Controls

Engineering controls, such as ventilation, and good work practices are the preferred methods of minimizing exposures to airborne lead at the worksite. The engineering control methods that can be used to reduce or eliminate lead exposures can be grouped into three main categories:

1. substitution;
2. isolation; and
3. ventilation.

Engineering controls are the first line of defense in protecting workers from hazardous exposures.

Substitution. Substitution includes using a material that is less hazardous than lead, changing from one type of process equipment to another, or even, in some cases, changing the process itself to reduce the potential exposure to lead. In other words, material, equipment, or an entire process can be substituted to provide effective control of a lead hazard. However, in choosing alternative methods, a hazard evaluation should be conducted to identify inherent hazards of the method and equipment.

Examples of substitution include:

• Use of a less hazardous material: applying a nonleaded paint rather than a coating that contains lead.
• Change in process equipment: using less dusty methods such as vacuum blast cleaning, wet abrasive blast cleaning, shrouded power tool cleaning, or chemical stripping to substitute for open abrasive blast cleaning to reduce exposure to respirable airborne particulates containing lead.
• Change in process: performing demolition work using mobile hydraulic shears instead of a cutting torch to reduce exposure to lead fumes generated by heating lead compounds.

Any material that is being considered as a substitute for a lead-based paint should be evaluated to ensure that it does not contain equally or more toxic components (e.g., cadmium or chromates). Because substitute materials can also be hazardous, employers must obtain a Material Safety Data Sheet (MSDS) before a material is used in the workplace. If the MSDS identifies the material as hazardous, as defined by OSHA's hazard communication standard (29 CFR 1926.59), an MSDS must be maintained at the job site and proper protective measures must be implemented prior to usage of the material.

Isolation. Isolation is a method of limiting lead exposure to those employees who are working directly with it. A method which isolates lead contamination and thus protects both nonessential workers, bystanders, and the environment is to erect a sealed containment structure around open abrasive blasting operations. However, this method may substantially increase the lead exposures of the workers doing the blasting inside the structure. The containment structure must therefore be provided with negative-pressure exhaust ventilation to reduce workers' exposure to lead, improve visibility, and reduce emissions from the enclosure.

Ventilation. Ventilation, either local or dilution (general), is probably the most important engineering control available to the safety and health professional to maintain airborne concentrations of lead at acceptable levels. Local exhaust ventilation, which includes both portable ventilation systems and shrouded tools supplied with ventilation, is generally the preferred method. If a local exhaust system is properly designed, it will capture and control lead particles at or near the source of generation and transport these particles to a collection system before they can be dispersed into the work environment.

Dilution ventilation, on the other hand, allows lead particles generated by work activities to spread throughout the work area and then dilutes the concentration of particles by circulating large quantities of air into and out from the work area. For work operations where the sources of lead dust generation are numerous and widely distributed (e.g., open abrasive blasting conducted in containment structures), dilution ventilation may be the best control.

Examples of ventilation controls include the following:

• Power tools that are equipped with dust collection shrouds or other attachments for dust removal and are exhausted through a HEPA vacuum system.
• Vacuum blast nozzles (vacuum blasting is a variation on open abrasive blasting). In this type of blasting, the blast nozzle has local containment (a shroud) at its end, and containment is usually accomplished through brush-lined attachments at the outer periphery and a vacuum inlet between the blast nozzle and the outer brushes. Containment structures that are provided with negative-pressure dilution ventilation systems to reduce airborne lead concentrations within the enclosure, increase visibility, and control emissions of particulate matter to the environment.

Source: OSHA

Certisafety Section Home Page