Carbide tips create health problems

March 1995

Workers who file saw blades or those who machine tools with tungsten carbide (or other "hard metal") tips may be exposed to toxic levels of cadmium, a cancer-causing agent, and cobalt, a suspected cancer-causing agent. Grinding and filing hard metals may produce high levels of exposure to cobalt, and brazing operations may create high exposures to cadmium. Even though employers use local ventilation and wet grinding methods, overexposure still may occur. According to medical studies, toxic effects of exposure may include kidney disease, asthma, anemia, emphysema, and hard metal lung disease with reduced lung function.

Q: What are "hard metals?"

A: Hard metals are metal alloys with properties of extreme hardness, wear-resistance, and high temperature stability.

Hard metals are used for cutting and drilling tools, as well as for metalworking dies and special machine parts.

Hard metal alloys are actually metal composites, made by mixing metal carbides and binder metals in powdered form, and then pressing the compound into desired shapes under high temperature and pressure.

Tungsten carbide is the most commonly used hard metal in the U.S. Cobalt is the most common binder metal.

The amount of cobalt in most hard metal alloys varies from as little as 2 percent up to 25-30 percent. Certain hard metals, such as "stellite," may contain more than 50 percent cobalt, although airborne cobalt exposures with stellite grinding may be lower than with grinding other hard metals.

Cadmium is common in the brazing solders used to attach hard metal pieces to other metal pieces.

Q: Which operations involve exposure to hard metals that could be a concern?

A: Currently, there are no businesses in Washington that are known to actually make hard metal. However, hard metals are commonly encountered here either as an existing component in a manufactured tool or as hard metal pieces used in manufacturing or reconditioning tools.

There is no evidence of substantial exposure to cobalt or cadmium during the actual use of tools containing tungsten carbide or other hard metal. But workers can be significantly exposed or overexposed to cobalt or cadmium during the manufacture or reconditioning of tools with hard metal parts, such as tungsten carbide-tipped saw blades.

Tooling operations that commonly produce exposure to cobalt or cadmium include: dry or wet grinding of hard metal tips/parts on saw blades or other metal tools, and brazing or welding hard metal tips/parts on to saw blades or other tools.

Workers who may be involved in these operations include tool makers, saw filers, grinders, machinists, brazers, welders and others.

These people may work in hard metal tool manufacturing firms, at businesses that recondition dull or broken hard metal tools, or in tool reconditioning or machining shops within larger businesses that use hard metal tools. Lumber mills, for example, commonly employ full-time saw filers who repair and maintain hard metal-tipped saw blades.

Other types of wood or metal product fabrication businesses also may have workers routinely involved in hard metal tool reconditioning.

Q: How are workers exposed to cadmium or cobalt in hard metal?

A: A number of inspections in the state have revealed worker overexposures to cadmium from brazing with cadmium-containing solder, from grinding or sand- blasting hard metal tools made with cadmium-containing solder, and even from grinding operations in which "cadmium free" solders were used to attach the hard metals.

Workers also can be exposed to cadmium by ingestion and through contact with cadmium in dust on hands and work surfaces.

Cobalt, which is a routine ingredient of tungsten carbide and other hard metals, may be released into air during the manufacture, finishing, grinding, filing, sharpening, brazing, welding, or sandblasting of hard metal.

Exposure could be in the form of cobalt metal fumes created when hard metal is brazed or welded to other metals, or as airborne cobalt metal produced by dry or wet grinding operations.

Grinding coolants commonly leach cobalt from ground hard metal, and the concentration of cobalt dissolved in coolant can increase over time. Even when hard metals are not actually being ground, wet grinding operations can generate a coolant mist that causes exposure to cobalt dissolved and suspended in the coolant.

All these forms of exposure could result in inhalation of cobalt by the worker at or near the operation. Monitoring of hard metal tool workers at manufacturing. Reconditioning worksites, as well as saw filers at lumber mills, has found many cases of worker overexposure to cobalt. It is not yet known if cobalt dissolved in coolant can be absorbed through the skin.

Q: What are the potential health effects from such overexposures?

A: Acute overexposure to cadmium fumes can cause chemical pneumonia or pulmonary edema (leakage of body fluid into the lungs).

The major adverse health effects associated with long-term exposure to cadmium are on the kidneys and lungs. Long-term overexposures to cadmium can cause irreversible kidney damage or emphysema, a permanent and potentially disabling condition.

The kidney damage typically produces abnormal levels of protein in urine, and one method for monitoring cadmium exposure involves measurement of a urine protein.

Cadmium is also known to cause lung cancer in humans with long-term excessive exposure, and is suspected as a cause of prostate cancer. Cadmium has been shown clearly to induce cancers in laboratory animals.

Cobalt exposures can cause either asthma or "hard metal lung disease" (inflammation or scarring of the lungs). Either of these lung conditions can develop quickly or over a long period of time, and can be associated with relatively low exposure levels.

Both conditions are potentially reversible if detected in early stages, but otherwise can progress rapidly or slowly to cause severe disability. Hard metal lung disease can be fatal. Cobalt is a definite carcinogen in animals, and a suspected carcinogen in humans.

Cobalt can cause skin sensitization and an allergic contact dermatitis (skin rash). Contact dermatitis is common in saw filers and tool grinders. It also may be caused by skin irritation from coolants or by sensitization to other metals, such as nickel or chromium.

Q: What are the "allowable" exposure limits for cadmium and cobalt?

A: Both the federal and state government set permissible exposure limits or "PELs" for exposure to airborne chemicals in industry.

The PELs are established at levels generally believed to ensure that nearly all workers will not suffer adverse health effects, even though they may be exposed daily to these levels in the workplace.

Exposure levels above the PEL are considered potentially harmful, and the law requires that employers ensure that employees are never exposed to levels over the PELs.

The current federal and state airborne PEL for cadmium is 5.0 micrograms per cubic meter of air (5.0 ) g/m3), calculated as an eight-hour time-weighted average.

In 1993, Washington adopted detailed safety and health requirements for protecting employees from overexposure to cadmium.

The rules are in the Washington Occupational Health Standards at WAC 296-62-074 (for general industry) and in the Safety Standards for Construction at WAC 296-155-174 (for construction).

The Washington airborne PEL for cobalt is 50 micrograms per cubic meter of air (50 g/m3), calculated as an eight-hour time-weighted average.

General health standards require ventilation and respiratory protection where overexposures to cobalt exist.

The American Conference of Governmental Industrial Hygienists has concluded that workplace exposures should not exceed 20 g/m3, calculated as an eight-hour time-weighted average (TWA).

A recent study by the University of British Columbia and a report published by the University of Washington each concluded that the existing PEL for cobalt should be lowered at least to 20 g/m3 (TWA), and preferably to 5-10 g/m3 (TWA), to provide adequate protection for workers exposed to cobalt in the form of hard metal. Employers are not required to control cobalt exposures any lower than the 50 /m3 PEL, but it is prudent to do so.

Q: How do I monitor or assess if hard metal workers are being overexposed to cadmium or cobalt?

A: First, be sure you know of all operations where cadmium containing solders are used.

Identify any operations where tools with hard metal tips/ parts (containing cobalt) or with metals containing cadmium are being finished or reconditioned through processes such as brazing, welding, grinding, filing or sandblasting.

If you are not sure whether cadmium or cobalt exists in your workplace, check the Material Safety Data Sheets (MSDS) that must be provided by manufacturers of materials containing hazardous ingredients.

If you identify operations that could lead to cadmium exposures, initial monitoring of the air breathed by exposed workers is required. If you think cobalt exposures are possible, you are required to make sure cobalt exposures do not exceed the PEL. Compliance with this requirement can only be confirmed with air monitoring.

When monitoring for cobalt, one should also monitor for cadmium, because cadmium overexposures have been documented even when cadmium containing solders were not being used.

Monitoring, sample analysis, and interpretation of monitoring data is a specialized technical process that may be conducted by company hygiene professionals, hired safety and health consultants, or government or university occupational health consultants. Government or university hygiene consultants may provide initial monitoring free of charge, especially to small employers.

It is important to note that if a worker is exposed to a hazardous substance, such as cadmium or cobalt, a number of factors determine whether harmful health effects may occur, and the type and severity of effects. These factors include:

• How much of the hazardous substance the worker is exposed to.

• How long workers are exposed.

• Whether the substance is inhaled, ingested, or comes in contact with the skin.

• Which other chemicals the worker may be exposed to.

• Characteristics of individual workers.

Good initial monitoring helps to identify these factors and provides the best possible evaluation of each worker's exposure.

Q: If monitoring reveals overexposures to cadmium or cobalt, what are my obligations under current safety and health laws?

A: Cadmium exposure in excess of the allowable permissible exposure limit (PEL) is a serious occupational health concern.

In the case of cadmium, even exposures over the "action limit" (2.5 g/m3), which is one-half the PEL (5.0 g/m3), are a significant health concern.

If worker exposures exceed the cadmium action limit, an employer must meet applicable sections of the general industry cadmium standard (WAC 296 62-074) or the construction industry cadmium standard (WAC 296-155-174).

Major sections of these standards require periodic exposure monitoring; establishing special "regulated areas"; engineering and work practice controls; respiratory protection; protective work clothing and equipment; clean change rooms, showers, hand-washing facilities, and lunchroom facilities; general housekeeping; medical monitoring of exposed workers (and removal of workers, if necessary); training; and recordkeeping.

The general and construction industry cadmium standards require that employers provide a medical monitoring program for workers with cadmium exposures above the action limit.

In some cases, the standards also require that medical monitoring be provided for workers who have acceptable or even no cadmium exposure at the present time, but who had higher exposure in the past.

The federal Occupational Safety and Health Administration has developed a computer program, "GOAD," that can help physicians and others in the decision-making process associated with the biological monitoring program required by the cadmium standard. This computer program is available through the Labor News Bulletin Board (202-219-4784) and the Cadmium Council (703-7091400). OSHA also makes GOCAD accessible on Internet by FTP to GABBY.OSHASLC.GOV through anonymous logon.

Current state regulations require only that a worker's airborne exposure to cobalt be limited to less than the PEL (50 g/m3). However, in view of the mentioned recommendations, it is prudent to strive for cobalt exposures well below the PEL.

The University of Washington report strongly recommended that periodic medical monitoring be offered to workers exposed to cobalt from hard metal to help early detection of symptoms of hard metal lung disease or asthma. Although this is not required by law, it is prudent to do so.

Q: What type of controls are available to eliminate or reduce exposures?

A: The best control for cadmium exposures is to eliminate the use of cadmium, such as by replacing cadmium- containing solder or "filler metals" with cadmium-free materials for brazing operations.

Cadmium-free solders are commercially available for a wide range of applications, and tool and saw blade manufacturers have successfully used them in many situations.

If a cadmium-free material cannot be used, another option is to physically confine the process and provide an efficient local air exhaust system to vent cadmium fumes away from the breathing zone of workers.

Hard metal workers should be protected from cobalt overexposures through proper confinement and local exhaust of certain operations, such as dry or wet grinding.

Local exhaust or confinement systems should be designed and tested by qualified individuals to ensure that the systems are effective in controlling exposures.

Workers may need to wear proper respiratory protection to protect themselves from exposures until the confinement or local exhaust system is set up, tested, and shown to reduce exposures effectively. However, respirators should not be considered a satisfactory long-term solution to exposure control.

Using respirators as an interim control measure requires that the respirators be chosen properly and fit-tested, and that the other requirements of the respirator standard (WAC 29662-071) be satisfied.

To minimize exposures through ingestion, consumption of food, beverages and tobacco products should not be allowed in areas where exposures could occur. In addition, workers should wash their hands before eating, drinking, smoking or applying cosmetics.

Q: How can I get help in evaluating, controlling, or eliminating exposures of hard metal workers to cadmium and cobalt?

A: To the extent practical, be proactive to prevent the possibility of occupational health hazards for workers potentially exposed to cobalt or cadmium at your workplace.

Thoroughly explore all available options for help in evaluating and, if necessary, controlling or eliminating worker exposures to cadmium and cobalt.

Contact manufacturers of cadmium-free solders and work with them to find a product that will work well for your particular application.

Be aware that wet grinding does not necessarily control exposure hazards, and that dust levels that are not visible could still cause overexposures.

Work with company professionals or hired consultants to identify, install, and test confinement or local exhaust systems that will provide adequate exposure control for workers at brazing or hard metal grinding stations, or at other locations where cadmium or cobalt exposure could occur. Fully enclosed and ventilated saw sharpeners are commercially available.

Call government, university or private hygiene consultants to get information and help on how to comply with existing safety and health regulations or how to set up a medical monitoring program for employees exposed to cadmium or cobalt.

Train employees on the signs, symptoms, and prevention of cadmium and cobalt health hazards.

Workers should be advised to report all breathing difficulties that occur at work, even those for which there may be no obvious cause.

For more information: If you have other questions, please contact the industrial hygiene consultants in the L&I regional office nearest you. Look in the telephone directory under "Washington, State of, Department of Labor & Industries."

If your company would like more information on this serious health hazard, please contact a Labor & Industries consultant in your area.


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