Metalworking fluids and mist control
Greater safety, but greater costs

by Kevin Devine

As a metalworking tool cuts into the metal, pressures can exceed 400,000 pounds per square inch (psi), creating temperatures of up to 800 degrees C.  Cutting fluids absorb and carry away much of this heat, reduce friction, and protect the working surfaces.  The fluids also reduce the power needed to operate the tool and to flush debris from the site.

Cutting fluids are a key ingredient in metalworking, but new rules based on reported health risks will change how manufacturers handle, use and protect workers from these compounds.

Some tests show that workers exposed to the aerosol created from using the metalworking fluids face several hazards such as skin irritation (dermatitis and acne), respiratory irritation (pneumonia and asthma) and possibly cancer.

Further, a 1992 study published in the Scandinavian Journal of Work, Environment & Health suggests that metalworkers face a higher risk for cancers of the larynx, rectum and bladder than the general public.

Because of this study and concern for the safety of their members, the United Auto Workers (UAW) filed suit in 1993 petitioning OSHA for emergency release from the existing metalworking oil aerosol standards.  The UAW wanted the existing standard of 5 mg/m3 reduced immediately.  It believed, and NIOSH subsequently agreed, that lowering the standard would improve worker health and continue the decreasing trend of respiratory disease in metalworkers.

Getting the straight answers
In 1995, the UAW and American Automotive Manufacturers Association (AAMA) sponsored the first of several symposia on the issue.  Technical papers and studies presented at these meetings suggested the existing standard was probably too high for optimum safety, but issues were also raised about the validity of the studies.  For example, the original NIOSH study looked at metalworkers exposed to higher mist concentrations than those common today.  The studies also focused on fluids that are no longer available which leads some to question the validity of applying these studies to today’s metal workers.

In early 1998, NIOSH filed a final criteria document recommending a new metalworking mist standard: 0.4 mg/m3 of air as a time-weighted average concentration for up to 10 hours per day.  The recommended standard is measured as thoracic particulate mass, which means it is measured below the larynx in the respiratory system.  If the new standard is measured on the old basis of total particulate mass, it corresponds to approximately 0.5 mg/m3, or 10% of the previous level.

Technically, there is no existing standard for metalworking aerosol, says Dennis O’Brian, director of the Engineering Control Branch at NIOSH.  

“What currently exists is an oil mist standard, but because relatively few sites still use straight oil, the standard is greatly outdated,” he says.

Simple methods of reducing aerosol concentrations have been known for years, which includes everything from opening windows to enclosing machining lines.  The new standards will require more sophisticated means of removing aerosol exposure, such as filtration systems and increased fluid maintenance.

Ventilation systems can control mist by sucking the contaminated air into a removal or filtration system or by providing positive air pressure which isolates harmful aerosols and replaces contaminated air with fresh air.

Aerosols can be isolated using enclosure hoods provided by the original equipment manufacturer or added later.  However, retrofit enclosures tend to be less effective than those from the manufacturer.

Mist collectors and filters provide another method of removing contaminated air.  Available filter systems include media filters, electrostatic precipitators and centrifugal impact filters.  Each has its advantages and disadvantages and there is a tradeoff between initial cost vs. operating and maintenance costs.

Select the right fluid first
Experts say the best way to reduce exposure to metalworking aerosols is through proper metalworking fluid selection, use and maintenance. 

“Regardless of the mist concentration, metalworking fluids are probably safer today than years ago,” says Bill Lucke, manager of environmental science for Cincinnati Milacron.  “Worker safety can increase substantially when you use metalworking fluids more intelligently.  Regulations only put a box around the problem.  Using fluids correctly helps solve the problem."

Some steps your shop can take to improve metalworking fluid maintenance include keeping the fluid at the correct storage temperature.  NIOSH experts report that lower fluid temperatures are better because they help stabilize the fluid and reduce microorganism growth.  Other steps include monitoring and maintaining the correct fluid concentration and pH, applying the fluid at the lowest possible pressure and flow volume and regular maintenance of fluid recycling and filtering systems.

Some of the risk of inhaling metalworking aerosols comes from inhaling bacteria and fungi that develop in the metalworking fluid.  This problem requires careful fluid monitoring and appropriate biocide use to minimize microbial growth.  But because microbes can exist throughout the workplace, controlling worker exposure is a larger issue. 

“Microbes can grow in sources other than metalworking fluids, so just reducing the mist isn’t going to solve the problem,” says Lucke.

Finally, NIOSH recommends metalworking shops integrate their efforts to reduce metalworking mist with a complete program to increase worker awareness and safety.  Increased worker training in sanitation and hygiene, providing workers with protective clothing and equipment and periodic medical examination for workers at risk can greatly reduce the possibility of health problems from metalworking coolants.

Meeting the new standard will be expensive.  Based on a study by Robert Kramer of Ford Motor Company’s transmission and chassis operations, the cost to enclose a single metalworking machine could exceed $10,000.

Applied to an entire plant, the automaker is looking at over $8.5 million per million square feet, with nearly half a million dollars a year in operating costs.  Applied to the entire U.S. metalworking industry, the total could reach $10 billion, experts project.

This article appeared in the June/July 1998 issue of MRO Today magazine.  Copyright, 1998.

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