Protecting Workers Exposed to Lead-based Paint Hazards
A Report to Congress
 

DHHS (NIOSH) PUBLICATION NO. 98-112
JANUARY 1997

Chapter 4
METHODS, DEVICES, AND WORK PRACTICES TO CONTROL OCCUPATIONAL LEAD EXPOSURES DURING LEAD-BASED PAINT ACTIVITIES

Controls for LBP activities on steel structures

• Alternatives to traditional abrasive blasting

• Controls for abrasive blasting removal of LBP

• Respiratory protection for work on steel structures

• Occupational exposure assessment

• Alternate abatement processes

• Wet methods

• Vacuum power tools

• General dilution ventilation and containment structures

• Administrative controls

• Steel structures maintenance

• Residential lead abatement and renovation activities

The primary reason that existing highway bridges and industrial steel structures are repainted is to prevent corrosion that can cause the structures to collapse. In 1993, OSHA estimated that more than 3,700 bridges containing LBP are repainted each year.¹ The same report estimated that more than 13,000 painting jobs involving LBP are done annually on water storage tanks, fuel storage tanks, and industrial steel structures. Although the use of LBP application has declined significantly during the past five years, existing steel structures coated with LBP (approximately 90 percent of highway bridges) will need repainting and maintenance over the next 20 years.²

The most common method for repainting steel structures involves removing the existing coatings with open abrasive blasting. This method creates hazardous air concentrations of lead, other heavy metals, and when silica abrasives are used, silica.^3,4,5 In the past few years, contractors have been required to contain paint chips, dust, and waste abrasive materials during paint removal, typically with mesh tarpaulins or rigid structures, to protect the environment.^6,7 Unfortunately, the containment structures which control environmental emissions often increase workers' risks of hazardous exposures to lead and other materials by concentrating these agents. Lead exposures during dry abrasive blasting have been reported as high as 600 times the OSHA PEL.⁸

Below is a method-by-method evaluation of controls used in the steel structure repainting industry to reduce airborne lead and silica exposures of workers. Most of the data reported in this chapter and summarized in Table 4.1 are taken from NIOSH reports. Data from other published sources were used for those controls that NIOSH has not studied. Employers may find that occupational lead exposures in their workplaces differ from those described below. Lead exposures in the construction industry are highly variable. The most important variables for exposure measurements during construction activities are the method used, the contractor's work practices, preexisting surface lead concentrations, environmental conditions, engineering controls used, and sampling methods.

Alternatives to Traditional Abrasive Blasting

Overcoating

Overcoating is the application of a new coating on top of existing coatings; this was made possible by the design of specific overcoating products. This is similar to interim controls or in-place management, which are common alternatives to abatement of LBP in housing. Because much less of the existing LBP is removed or disturbed during overcoating, it reduces the potential risk to worker health. In most cases, areas with corrosion or deteriorated paint are repaired before overcoating the whole structure.

The first step of the overcoating process, washing the surface, is designed to remove accumulated salts and dirt, but not the intact paint coatings. Then a penetrating primer is used to coat exposed steel and rusted areas. The final step is application of a topcoat (or coats) over the entire structure. Overcoating advantages are (1) little waste generation or disposal; (2) no containment structure; (3) no (or very little) airborne lead generated; (4) lower project costs; and (5) the lead-based coating continues to provide excellent corrosion protection. The disadvantages are that the longevity of the overcoating is dependent on the quality of the old coatings and the LBP may need to be removed at some later date.

When feasible, overcoating may be the best way of reducing hazardous lead and silica exposures during steel structure repainting and repair work. It may prove to be a satisfactory alternative over the useful life of a structure. However, overcoating cannot be used in every situation, i.e., on surfaces with poorly bonded old paint. Additional research is needed to develop and evaluate overcoating programs, to improve surface-tolerant coatings, and to evaluate life-cycle costs for steel structures such as bridges and water tanks.

Chemical Stripping

Chemical stripping involves spraying an alkaline chemical on the painted surface, allowing it to react, and then scraping the decomposed paint and excess caustic from the steel surface. The surface is subsequently rinsed with water followed by quick abrasive blasting to remove traces of remaining paint and to establish a suitable surface profile, or anchor pattern, for repainting. Liquid runoff and solid wastes are collected using plastic sheets under the structure.

Worker lead exposures during the chemical spraying, scraping, and rinsing at one chemical stripping site evaluated were below the OSHA PEL.⁹ However, during the abrasive blasting that followed, high air lead (100 times the PEL) and alkaline dust concentrations occurred. A positive factor was that the time required for this quick abrasive blasting (and thus the total lead exposures) were reduced to about half that of normal abrasive blasting. The tradeoff is that the process introduces an additional chemical exposure hazard to the eyes, skin, and upper respiratory tract.

If the final blasting step could be eliminated by painting directly after the rinsing process, the chemical stripping process would be much safer. If abrasive blasting is needed to prepare the surfaces for repainting, it may be possible to improve the rinse method to reduce the airborne lead concentrations during subsequent blasting.

Wet Blasting

Wet methods have been used to reduce dustiness associated with LBP removal projects. Both high-pressure water alone and water mixed with abrasive have been used. Dust levels are reduced by the presence of water, but the extent of reduction is not presently known. Wet methods reduce the airborne lead concentration, but not necessarily below the PEL. NIOSH evaluated this process at a demonstration site and found an airborne lead concentration 30 times the PEL.¹⁰

Disadvantages are that the contaminated water may be difficult to contain and collect, and may be considered a hazardous waste. Also, water-soluble rust inhibitors are often used in this process to prevent rusting; however, their long-term effectiveness with new coatings is unknown.

Power Tools

Power tools can be used to sand, scrape, or chip coatings from steel structures. Power tools are often used to remove deteriorated paint from specified areas of a steel structure while leaving paint in nearby areas intact. The need to apply power tools firmly against the surface at all times can create worker fatigue and musculoskeletal hazards, and some tools may not be able to clean irregular surfaces. Another limitation of power tools when compared to abrasive blasting is that the production rate for paint removal is much less.

NIOSH has measured worker lead exposures up to 70 times the PEL during use of electric wire brushes and four times the PEL during use of pneumatic hammers (chisels).¹¹

Power tools equipped with HEPA-filtered LEV systems, also known as vacuum tools, are used to reduce worker exposures during LBP removal. Vacuum tools also reduce airborne lead emissions and hazardous waste volume. NIOSH has not tested the effectiveness of LEV systems on power tools, but studies indicate that vacuum tools reduce, but do not eliminate hazardous worker lead exposures. For example, airborne lead concentrations of up to 10 times the PEL have been reported for operators of vacuum needleguns.¹² On the other hand, a U.S. Environmental Protection Agency (EPA) study of LBP removal on highway bridges found that lead exposures of vacuum needlegun operators were very low (none detected), compared to exposures of 100 to 890 µg/m³ for conventional abrasive blasting on a similar bridge.¹³ In the same study, the EPA reported that the estimated project cost using vacuum needleguns was 33 percent higher than during conventional abrasive blasting, although 97.5 percent less hazardous waste was generated.

Vacuum tools are effective in controlling lead exposures when they are used properly. The tool must be held firmly against the surface at all times during paint removal for effective capture of lead dust.

Additional research is needed to provide LEV specifications for power tools, evaluate the effectiveness of LEV systems, and analyze the cost effectiveness of power tools with LEV compared to abrasive blasting with containment.

Controls for Abrasive Blasting Removal of LBP

Isolation/Automation During Blasting

Isolation is a very promising method under development for removing the worker from the airborne lead environment. The blasting process can be automated and conducted inside an enclosure while workers are stationed safely outside. At one test site, airborne lead concentrations in samples taken in the work area outside the enclosure were below the PEL.¹⁴ Typically, as much as 80 percent of the steel on some structures can be automatically blasted, and traditional methods could be used for the remaining areas. This technology is currently being tested on a limited basis and is not generally available.

Vacuum Blasting

Vacuum blasting is a method that uses specialized abrasive blasting equipment equipped with LEV. The exhaust system contains and collects dust at the generation source before the dust can escape. Vacuum blasting can greatly reduce the airborne emissions and the amount of hazardous wastes generated. This method is safer, but less productive, than traditional open abrasive blasting, and may not be suitable for irregular surfaces. The vacuum blasting nozzle must be held firmly against the work surface and therefore may cause worker fatigue and musculoskeletal hazards. A NIOSH survey of vacuum blasting found operators' lead exposures equal to the PEL.¹⁵ Research is needed to support consensus specifications for vacuum blast equipment.

General Dilution Ventilation

General dilution ventilation is used with some containment structures during LBP removal operations to provide negative pressure relative to the outside and reduce dust emissions. However, even with well-designed airflow patterns, workers near the abrasive blasting will still have hazardous lead exposures.

General ventilation designs and techniques vary greatly from site to site. In an in-depth survey at one site, NIOSH researchers found worker lead exposures as high as 400 times the PEL despite relatively good ventilation.¹⁶ Theoretically, ventilation techniques that provide fresh air directly to the worker and remove air near the lead generation source could significantly reduce lead concentrations in the breathing zone of workers. However, even well-designed ventilation systems are difficult to implement at construction sites because workers are continually moving around the structures. Research is needed to optimize ventilation parameters for containment structures.

Substitutes for Silica Sand Abrasive

Silica has traditionally been used as a material in the abrasive blasting process. However, because hazardous levels of airborne silica may accompany LBP removal projects, NIOSH recommends against the use of silica sand (or other substances containing > 1 percent free silica) as abrasive blasting material.⁴ Due to the prevalence of silicosis among blasters, the United Kingdom passed a regulation in 1949, and since then, a number of other countries, including Germany, Sweden, and Belgium have either partially or fully banned the use of silica sand for abrasive blasting material.^17,18,19,20 Substituting less toxic abrasive materials for the traditional high-silica-containing abrasive is becoming more common in the United States. The United States Navy has banned silica sand or any abrasive materials containing greater than 1 percent crystalline silica by weight for abrasive blasting on ships.²¹ However, even with a low-silica- content abrasive (<1 percent free silica), work in containment structures or in confined spaces may result in hazardous silica and lead exposures.²²

Respiratory Protection for Work on Steel Structures

NIOSH recommends engineering controls as the primary means of protecting workers. However, even with engineering controls, airborne lead exposures may greatly exceed the PEL during abrasive blasting and other paint removal methods. In these cases, respiratory protection is also necessary. When respirators are used, the employer must establish a comprehensive respiratory protection program as required by the OSHA respiratory protection standard (29 CFR 1910.134) and the construction lead standard (29 CFR 1926.62).

NIOSH-approved Type CE respirators are required for use by abrasive blasting operators (29 CFR 1910.94). The Type CE respirator with continuous flow and a loose-fitting hood or helmet is commonly used to protect workers during abrasive blasting. Based on the results of a simulated workplace study in 1995, OSHA indicated that for enforcement of the construction lead standard, certain Type CE respirators (Bullard Model 77 and Model 88) would be regarded as having an assigned protection factor (APF) of 1000 (protective for exposures up to 1000 times the PEL), provided that they were properly used.²³ In general, for lead exposures during abrasive blasting more than 25 times the PEL, NIOSH recommends the use of a positive- pressure, supplied-air Type CE respirator with a full (tight-fitting) facepiece, which has an APF of 2000. However, some contractors have reported that these more protective Type CE respirators are not feasible for outdoor work on steel structures because of inadequate peripheral vision and user comfort. To address these issues, manufacturers should design and seek NIOSH approval for improved respirators for outdoor abrasive blasting.

Table 4.1 Lead Exposures during LBP Removal on Steel Structures, NIOSH Sites

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