ABATEMENT METHODS
TRAINEE OBJECTIVES
After completing Section 6, you will be able to:
Substitution
Process/Equipment Modification
Isolation and Ventilation
Administrative Controls
INTRODUCTION
This section on work methods on steel structures provides general knowledge as to the type of construction activities associated with steel structures, bridges, and demolition that can cause exposure to lead. Also, we will look at what possible engineering controls and work practices can be used to reduce worker exposure. There are many tasks that Laborers perform that can cause very high lead exposure. These include abrasive blasting, welding, cutting, and burning.
This section will focus on lead related tasks, specifically the control of airborne lead, and the measures that can be taken to reduce exposure. Engineering controls (isolation, substitution, change of process, local exhaust ventilation, dilution ventilation) are listed for each task covered, as well as work practice controls.
ENGINEERING CONTROLS
There are three types of engineering control methods that are used by themselves or together to reduce or eliminate lead exposure:
Substitution
With substitution, we would replace the material with a less hazardous material such as using a non lead-based paint instead of a lead-based paint. Substituting one type of equipment for another, or in some cases even changing the process itself, is also a form of substitution. In other words, material, equipment, or an entire process can be substituted to provide effective control of a lead hazard.
Examples of Substitution
Process/Equipment Modification
The modification of the process used or modification of equipment -- for example, using a 6-foot cutting torch instead of a standard-length torch -- will increase the distance from the lead source to the worker's breathing zone, thus reducing the exposure.
Isolation
By isolating the process, exposure is reduced for all workers not involved in the task. A way of protecting these workers, and the environment, would be to erect a sealed negative pressure containment structure. For example, open abrasive blasting operations contained within a sealed negative pressure structure would help ensure that lead-bearing dust remains within the enclosure. Added precautions must be taken to protect those workers that must work within the containment.
Ventilation
There are two types of ventilation systems. The first type-and the kind that would be the best to have in cases where the material is highly toxic-is local exhaust ventilation. If a local exhaust ventilation system is properly designed, it will capture and control the lead at or near its source of generation and transport it to a collection system before it can be dispersed into the work environment, reducing the amount of lead in the air.
General ventilation is used to move large bodies of air through a room. For example, an exhaust fan in the ceiling provides general ventilation. Its purpose is to provide comfort. It must not be used to dilute hazardous material in a work area. In instances where the material is not highly toxic and where the sources of dust generation are numerous and widely distributed, general or dilution ventilation may be the best solution.
The degree of ventilation required depends on the method of paint removal and the type and condition of the paint. For example abrasive blasting of lead paint requires greater ventilation than hand tool cleaning of intact paint.
Examples of Ventilation
WORK PRACTICE CONTROLS
Good work practices can be vital aids for employers in achieving compliance with the OSHA exposure limit for lead, but more important is keeping Laborers and Ironworkers safe and healthy. Work practice involves the way a task is performed. Some fundamental and easily implemented work practices are: housekeeping, good personal hygiene practices, periodic inspection and maintenance of process and control equipment following proper procedures to minimize exposures in operating production and control equipment supervision and administrative controls.
Housekeeping
A good housekeeping program is required in 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 is 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. A regularly scheduled cleanup is especially important because it minimizes the re-entry of lead dust into the air, which can provide an additional source of exposure that engineering controls may not be designed to control.
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 (high efficiency particulate air) filters. Blowing with compressed air is generally prohibited as a cleaning method, unless the compressed air is used in conjunction with a local ventilation system designed to capture the airborne dust created by the compressed air, such as inside a containment structure.
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.
Inspection and Maintenance
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 which 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.
Performance of Task
In addition to the above work practice controls, workers must know the proper way to perform their job tasks to maximize the effectiveness of engineering controls. For example, if a worker inappropriately performs a task away from an exhaust hood, the control measure will be of no use. Failure to properly operate engineering controls may also contaminate the work area. Workers must be trained on safe operating procedures through fact sheets, discussions at safety meetings, and other educational and training means.
Supervision
Good supervision is another important work practice. It provides needed backup support for protection against mistakes. For example, by directing a worker to position the exhaust hood properly or to improve work practices, such as having the worker stand to the side of the cutting torch will reduce the worker's exposure to lead.
Administrative Controls
Administrative controls are another form of work practice controls that can be used to influence the way a task is performed. For example, employees' exposures can be controlled by scheduling production and/or workers' tasks in ways that minimize employee exposure levels.
The interim final rule for Lead in Construction requires that if the employer uses a job rotation schedule the employer must:
METHODS OF PAINT REMOVAL
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.
Typical structures to be cleaned with abrasive blasting include bridges, buildings, tanks and towers, pipe racks, pressure vessels, process equipment, supporting steel, and ships.
Open Abrasive Blasting
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 overspray, 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. The U.S. Environmental Protection Agency (EPA) has now promulgated regulations requiring the erection of containment structures for open abrasive blasting operations, to protect the soil, air, and water from lead.
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 due to waste material build-up on footing surfaces. This is where good engineering controls and housekeeping play an important part in eliminating slips and falls.
Contaminant structures vary in design and ability to contain debris. Containments or enclosures can be either partial or full enclosures. Partial containment consists of totally enclosing a section of a structure where active work is being performed, which is usually more convenient due to the large size of most structures and it is much easier to ventilate. Full containment is the total enclosure of all of a structure, and is usually difficult to accomplish due to the size of most steel structures.
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.
Engineering Controls
Work Practice Controls
Open Abrasive Blast Cleaning with Recyclable Abrasive
This system, like blast cleaning with expendable abrasive, uses compressed air to force the abrasive to the surface being cleaned. The difference, however, is that the spent abrasive and waste is collected and separated, and the abrasive reused. Blast cleaning with recyclable abrasive, such as steel grit or aluminum oxide, requires specialized equipment for vacuuming or collecting the abrasive for reuse, separating the lead dust from the reusable abrasive and, in the case of steel grit, maintaining clean, dry air to avoid rusting of the abrasive.
The abrasive cleaner must be extremely efficient in removing lead dust otherwise, lead is reintroduced into the containment, which when combined with the paint being removed, can increase worker exposures to lead. This method provides the same high-productivity and high-quality cleaning as blast cleaning with expendable abrasive, but the volume of debris generated is greatly reduced.
The containment area must be designed to ensure effective removal of waste and abrasive. Recycling equipment must be monitored to ensure waste is removed from the abrasive and not reblown into the containment area.
Vacuum Blast Cleaning
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 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.
Vacuum blasting has several disadvantages. It is more time-consuming than conventional open abrasive blasting, because the nozzle must be held close to the blast surface. Abrasive may escape if the brush attachments aren't completely sealed around the substrate because of operator fatigue, poor work practices, and small or irregular surfaces. Workers can't always see the blast surface because the vacuum system and brushes are in the line of sight, so some areas may need to be blasted repeatedly because they are missed on the first or second pass. Further, some blast heads are heavy, and workers may need to take more frequent breaks due to fatigue.
Wet Abrasive Blast Cleaning
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 rust inhibitors may be necessary to use to avoid rusting. The containment must also 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.
High Pressure Water Jetting
High pressure water jetting, up to 20,000 psi (pounds per square inch) uses a pressure pump, a large volume of water, a specialized lance and nozzle assembly and, in some cases, a supply of inhibitor to prevent rusting. High-pressure water can remove loose paint and rust, but will not efficiently remove tight paint or rust, and will not remove mill scale. If the original surface was blasted clean, the old paint can be removed to restore it to the original condition.
Because water is used, little dust is generated. The containment must be constructed for the collection of water, rather than to control dust emissions. The debris generated is made up of paint, rust, and water. If the lead debris can be filtered from the water, the volume of debris is low. Typically, 5 to 10 gallons of water per minute are used.
This system is efficient for removal of loose, flaky paint. It may not be efficient to remove tight paint. The productivity and the ability to remove tight paint, rust, and mill scale can be improved through the addition of abrasives into the water stream.
High Pressure Water Jetting with Abrasive Injection
This system uses an expendable abrasive material that is added into a pressurized water jet for surface preparation. Although airborne lead exposure is virtually eliminated, wet abrasive is more difficult to handle and move than dry abrasive, and the volume of debris also increases. Because the abrasive exposes the bare surface, inhibitors, such as sodium nitrate or amines are often required to avoid rusting.
Abrasives used for injection include sand and slag materials, as well as soluble abrasives, such as sodium bicarbonate. The sodium bicarbonate will not remove paint, rust and mill scale as efficiently as sand or slag abrasives. However, the advantage is that the abrasive is water-soluble, and if the lead can be filtered from the water, the volume of debris is reduced as the dissolved sodium bicarbonate is not hazardous.
Ultra High Pressure Water Jetting
Ultra-high pressure water jetting uses pressurized water from 20,000 to 40,000 psi. Ultra-high pressure water jetting is similar to high-pressure water jetting, except the higher pressures clean more efficiently, and are better able to remove tight paint and rust. In addition, the volume of water required is reduced, with less than 5 gallons per minute typically used.
The water reduces dust by mixing the dust into the water droplets and airborne lead exposures are virtually eliminated.
The greatest disadvantage to this process is the difficulty in collecting the contaminated water. Wherever the water goes, debris is carried along. Dust generation, debris generation, and the type of containment necessary are all similar to high-pressure water jetting. Inhibitors are also often required to avoid rusting. Mill scale is not removed, but if the surface was previously blast cleaned, the surface is restored.
Sponge Jetting
Sponge jetting involves the use of specialized blasting equipment that forces a combination of an abrasive material, such as steel or garnet, encased in a soft sponge (foam) material.
A damp sponge can remove dust without over wetting the surface, and can also break up the paint coating into larger particles.
The low dust generation can help reduce containment requirements, although screens and tarps will be necessary to separate the work area and to allow for the collection of the sponge and debris. Productivity is lower than open abrasive blasting using more traditional abrasives. This disadvantage is offset by not having to spend as much time building complex containment structures.
The debris generated is less than when using slag or sand abrasives because the sponge is recycled. The recycling unit uses a series of vibrating screens to remove large and small particulates for disposal.
Carbon Dioxide (Dry Ice) Blasting
Cryogenic (cold) cleaning involves blasting with dry ice pellets. A stream of dry ice pellets, at -100º F, moves at high velocity through a blast hose and nozzle. The pellets stick to the surface and then evaporate, leaving only paint debris for clean-up. The greatest advantage to carbon dioxide (CO2) blasting is that the blast material evaporates and needs no further handling or disposal.
The cost of cryogenic cleaning is expensive and it doesn't work as well with lead-based paints compared with other coatings. In addition, the production rate of CO2 blasting is slow compared to conventional abrasive blasting. And since only the paint is removed, to prepare the surface for coating the surface may need additional blasting with an abrasive to produce a rough surface to improve adhesion of the new coating on the surface.
Chemical Cleaning
Old paint can also 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.
The production rate of chemical stripping tends to be slow when compared to abrasive blasting, but the amount of lead released into the air is much less. Usually with chemical stripping, some abrasive blasting needs to be done to remove rust and mill scale prior to painting. As far as a health hazard, this rust removal step will still contain lead, but in reduced levels.
Power Tool Cleaning
Power tool cleaning involves the use of power-operated impact, grinding, or brushing tools. Power tools available for paint removal include needle guns, disk sanders, grinders, power wire brushes, rotary hammers, and rotary peeners. Each of these tools can be used with or without local exhaust ventilation. Health hazards associated with power tool cleaning are created due to the large amount of lead dust and paint chips generated.
Engineering and Work Practice Controls:
Hand Scraping of Lead-based Paint
The hazard of hand-held scraping comes from dust generation and paint chips released from the scraping process.
Engineering Controls:
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.
Engineering Controls:
WELDING, BURNING, AND TORCH CUTTING
High levels of lead are emitted when welding or burning takes place on lead-painted steel structures. The exposure can come 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 you add lead paint to it, it compounds the hazard. 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.
Engineering and Work Practice Controls:
BABBITTING
Babbitting is a process where molten metal (either lead or zinc) is used to anchor wire cable into a socket. It is commonly found on bridge support systems or cranes used on job sites to lift materials into place. Basket sockets or what is sometimes referred to as Zinc or Spelter Sockets are efficient and permanent terminal attachments for wire rope. They are the most reliable of all terminal fittings and when properly attached, these standard drop forged sockets are 100% efficient. They are recommended for all standing ropes and during severe conditions. When lead is used in babbitting, the worker must be informed of the hazardous fumes that can be released into the air. It is recommended that during babbitting, engineering controls and/or respiratory protection be used in compliance with the OSHA Lead in Construction Standard. Only trained and qualified personnel should be permitted to make these connections. A basket socket is usually attached to the end of a wire rope with molten zinc or babbitt metal, and becomes a permanent end fitting. Lead is also used but zinc is considered to have 4 times the strength of lead.
Procedures for Babbitting
Once the wire rope is seized at the proper point, take each strand and separate each wire. Cut the hemp center at the seizing. Clean the wire well with a solvent and then a dilute solution of muriatic acid. Ensure that personal protection is used during exposure to the liquids. Once this step is complete, wash them with a boiling soda solution without any acid or solution penetrating beyond the end of the seizing. At this point draw the end of the wire together and apply a temporary seizing and force the socket down over the end of the wire. Remove the temporary seizing and bend each wire over about one-half of an inch from the end. Pull the wires down into the socket, place putty or clay into the socket to prevent the molten metal from escaping. Fill the basket with the molten metal. As soon as the metal becomes solidified, plunge the metal into water to cool. Remove the putty or clay. You are now ready to put the wire back into use.
INDUSTRIAL VACUUMING
The use of an industrial vacuuming system to remove lead dust from surfaces is a highly recommended procedure. There are many companies that provide the service of cleaning catwalks, structural beams, and plant floors to reduce the exposure for the plant workers to lead and other hazardous metals. These plants can include non-ferrous metal plants or steel plants melting lead-containing scrap in an electric air furnace. The use of HEPA filters on the exhaust air outlet is recommended.
ASSOCIATED MISCELLANEOUS ACTIVITIES
In construction, as in other trades, there are many jobs in which Laborers and Ironworkers are exposed to chemical hazards, including metals, such as lead, that are produced by workers in other trades. We all must become aware of what is happening around us if we are to remain safe and healthy.
Enclosure Movement
This involves the setting up, tearing down and handling of nylon, plastic, and cotton tarpaulins, as well as enclosure framing members that are used to enclose lead dust and fumes. Projects, such as the abrasive blasting of bridges, elevated highways, water towers, and storage tanks involve some type of containment structure.
The sequence of events for a bridge project involves the setting up of a containment structure to protect the environment from the lead debris. After the area in containment is blasted clean and primed, the containment is taken apart in order to move it to a new section to be worked on. It is the removing of the tarpaulins and the framing that allows what ever dust and debris that had settled to be re-released into the air causing workers to be exposed to lead. The structure needs to be cleaned with a HEPA vacuum and wet wiped prior to movement of the enclosure.
Engineering Controls:
Because of the mobile nature of this task, it is not feasible to use any type of ventilation system to reduce exposures.
Miscellaneous Abrasive Blasting
Not only are the workers who do the abrasive blasting exposed to high levels of lead, but anyone working at the site could also be potentially at risk of exposure. Welders and burners working outside and downwind of the lead abatement area could be exposed to lead traveling with the air currents. Other workers can be exposed to lead due to the dispersion of the dust from the abrasive blasting. These workers may be involved in supporting activities, operating recycling and vacuum truck equipment, or tending the abrasive medium transfer and waste removal equipment. Lead exposure can also result from hose connection leaks, the changing of waste drums, malfunctioning recycling equipment, and the cleanup process itself.
Engineering Controls:
Because of the outdoor and stationary nature of these activities, it is generally not possible to use ventilation equipment to reduce lead exposures.
Work Practice Controls:
Regular inspections and timely maintenance of all equipment will eliminate dust leaks and prevent equipment malfunctions.
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ASSIGNMENT SHEET
Process/Equipment Modification
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