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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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Publication Number: FHWA-RD-98-179
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Bridge Lead Removal and General Site SafetyWork Methods on Steel Structures
Table of Contents
This section on work methods on steel structures will give workers general knowledge as to the type of construction activities associated with steel structures, bridges, and demolition that can cause exposure to lead. It also looks at what work practices can be used to reduce worker exposure. Many tasks that workers perform can cause very high lead exposure, including abrasive blasting, welding, cutting, and burning. A good housekeeping program is required on all jobs to keep airborne lead levels below permissible limits. Good housekeeping can be as easy as setting up a schedule to make sure that accumulations of lead dust and lead containing debris are reduced to a minimum. Lead dust in the workplace on overhead ledges, equipment, floors, and other surfaces must be removed before disruption like traffic, vibration, or random air currents can cause dust to become airborne again. Such cleaning operations should be conducted whenever possible, and always at the end of each day and after normal operation ceases. Furthermore, everyone doing the cleanup should be provided with suitable respiratory protection and personal protective clothing to prevent contact with lead. Vacuuming is considered to be the most reliable method of cleaning surfaces on which dust accumulates. When vacuuming equipment is used, the vacuums must be equipped with HEPA filters. Blowing with compressed air is generally prohibited as a cleaning method. All lead-containing debris and contaminated items accumulated for disposal must be collected and put into sealed, impermeable bags or other closed, impermeable containers. Bags and containers must be appropriately labeled as lead-containing waste. Scheduled inspection and equipment maintenance, such as for ventilation systems, is another important work practice control. At work sites where total containment is used as an engineering control, the failure of the ventilation system in the containment area can result in high levels of lead exposure. Often, equipment that is near failure will not perform normally. Regular inspections can detect problems so that timely maintenance can then be performed. If equipment is routinely inspected, maintained, and repaired, or replaced before equipment failure happens, there is less chance that hazardous exposures will occur. In addition to the above work practice controls, workers must know the proper way to perform their jobs. For example, if a worker inappropriately performs a task away from an exhaust vent, the exhaust vent will be of no use. All training will be provided by the employer. Good supervision is critical. It provides needed backup support for protection against mistakes. For example, directing a worker to position the exhaust vent properly or improving work practices, such as by having the worker stand to the side of the cutting torch, will reduce the worker's exposure to lead. The most common method of removing lead-based paint from steel structures is open (nozzle) abrasive blasting. The abrasive material, generally steel shot/grit, sand or slag, is forced by compressed air through hoses. The material cleans the surface of the structure, exposing the steel. The abrasive also conditions the steel, which improves the adherence of the new paint or weld. Until recently, abrasive blasting work was conducted in open air, which helped to reduce the airborne concentration of abrasive dust containing lead in the workers' breathing zone. Tarpaulins were generally used only to protect neighboring homes and automobiles from a damaging blast of abrasive dust or to reduce residents' complaints about over spray, dust, and dirt. Now that the health effects are clearly known, it is even more important to ensure that lead-containing debris does not contaminate the surrounding area. Regulations now require the erection of containment structures for open abrasive blasting operations. Although containment structures are designed to reduce the release of lead into the environment, they usually increase worker exposure to airborne lead inside the containment, reduce visibility, and increase the risk of slip and fall injuries resulting from waste material buildup on footing surfaces. Contaminant structures vary in design and ability to contain debris. Some containment structures consist of tarpaulins made of open mesh fabrics (screens) that are loosely fitted around the blasting area; some use rigid materials, such as wood, metal, or plastic to enclose the blasting area, and some use a combination of flexible and rigid materials. Large air-moving devices may be connected to an enclosed containment structure to exhaust dust-laden air and create negative pressure inside the containment. These steps should be followed:
Vacuum blasting is a variation on open abrasive blasting. The blast nozzle has local containment (a shroud) at its end, usually accomplished by brush lined attachments at its outer edges and a vacuum inlet between the blast nozzle and the outer brushes. The brushes prevent release of the abrasive and debris as they rebound from the steel surface. These particles are removed from the work area by the built-in vacuum system. The abrasive can be disposed of or cleaned and recycled. Vacuum blast cleaning is the most efficient method, with minimal dust generation if used properly, except where accessibility is difficult, such as between back-to-back angles. A variety of heads are available to achieve a tight seal for inside corners, outside corners, and flat surfaces. The advantages of vacuum blasting are that most of the waste materials and abrasive are collected at the site of generation and are not transported to the breathing zone of the workers, and the need for containment may be reduced or eliminated. Wet abrasive blast cleaning is a modification of traditional open abrasive blast cleaning. This system uses compressed air to propel the abrasive material to the surface being cleaned. Water is injected into the abrasive stream either before or after the abrasive exits the nozzle. The water reduces dust levels and minimizes the need for the containment enclosures, which would be required for dry blast cleaning. A disadvantage to using water is that it may be necessary to use rust inhibitors to avoid rusting. The containment also must be designed to capture the water. Wet abrasive/paint debris is more difficult to handle and transport than dry debris, and unless the water can be filtered, it may add to the volume of debris generated. Old paint also can be removed from steel structures using chemical strippers. These strippers can be solvent- or caustic-based and be applied by hand or sprayed on. Depending on the thickness of the paint, the chemical remains on the surface anywhere from 5 minutes to 48 hours. After the chemical has had time to do its job, scraping and brushing are used to clean the chemical and paint off. Pressurized water may also be used. It is very important that all of the waste is contained so it will not contaminate the environment. Chemicals used can be hazardous. They can be inhaled, ingested, or absorbed through the skin. Many of these chemicals will cause eye and skin irritation or burns. It is very important to ensure that workers are protected from not just the hazards of lead but also the chemicals. Proper training in the use of chemical strippers must take place. Respirator cartridges and protective clothing must be selected for the specific chemicals that are used. Hand Scraping of Lead-based Paint The hazard of hand-held scraping comes from dust generation and paint chips released from the scraping process. A wet method with a HEPA vacuuming ventilation system should be used. Heat Gun Removal of Lead-based Paint In this process, a heat gun, which is similar to a hair dryer, is used to peel paint away. This process uses heat to separate the paint from the steel structure and the paint can then be removed with a putty knife. The health hazards associated with this process come from lead fumes released into the air during the heating process and from lead paint chips created from the scraping. Heat guns should be restricted to 700°F (371°C) by using a built-in thermostat. Above this temperature lead is vaporized into the air. Commercial heat guns can produce temperatures as high as 1000°F (538°C), generating and releasing high levels of airborne lead. WELDING, BURNING, AND TORCH CUTTING IN MAINTENANCE, RENOVATION, AND DEMOLITION High levels of lead are emitted when welding or burning takes place on lead-painted steel structures. Exposure can result from a large variety of construction projects, from bridge rehabilitation to demolition of a high-rise building. Welding is a process that joins two pieces of metal together, generating many hazardous compounds from the metal itself. When lead paint is added to it, the hazard is compounded. Cutting metal with lead coating on it results in the same problems as welding. Both welding and cutting cause the metal and its coating to be released in the air as fumes, making it available for inhalation by workers.
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