Machine coolant alone can be dangerous.  It is not meant to be breathed.  Fortunately air handling equipment is easy to install and pretty inexpensive.

The real health problems arise when machine coolant is mis-handled and bacteria in machine coolant is allowed to grow and metals are allowed to contaminate the machine coolant.  For more information on Machine Coolant and finding a coolant management plan that will increase work safety visit our Coolant Filtration Index.

For a Healthier Work environment Try filtering your Machine coolant.  See the difference that filtering your machine Coolant can make in your shop.  For more information check out our blog on machine coolant filters.

Using a machine coolant filter unit will also greatly reduce the amount of bacteria and contaminates in your machine coolant and reduce exposure to these health risks.

Bacteria Problems

Occupation Mortality in Washington State 1950 – 1989 http://www.cdc.gov/niosh/pdfs/96-133.pdf

Wood / Lumber / Sawmill Workers, Occupation Code 974, Total deaths 19,395 

Bacterial infections are caused by the presence and growth of microorganisms that damage host tissue. The extent of infection is generally determined by how many organisms are present and the toxins they release. Worldwide, bacterial infections are responsible for more deaths than any other cause. Symptoms can include inflammation and swelling, pain, heat, redness, and loss of function. The most important risk factors are burns, severe trauma, low white blood cell counts, patients on immunotherapy treatment, and anyone with malnutrition or vitamin deficiency.

Bacteria are generally spread from an already infected person to the newly infected person. The most common invasion routes are inhalation of airborne bacteria, ingestion into the stomach from dirty hands or utensils, or through contaminated food or water, direct contact with an infected area of another person's body, contaminated blood, or by insect bite. 

Disease group: bacteria - Condition count: 97

Classes: classes list

Metalworking Fluids Health Effects 

Skin Problems

Skin problems such as irritation, rashes, and dermatitis are common among people exposed to metalworking fluids.

Cancer

We have known for a long time that exposure to metalworking fluids can cause skin cancer. Machinists who put oily rags in their pants pockets sometimes developed scrotal cancer. 

In the mid-1980s U.S. studies started to show that workers exposed to metalworking fluids were developing various kinds of cancers.  In the summer of 1992 a major study of General Motors workers in the United States showed excess levels of a number of different kinds of cancers. This GM / UAW study of 46,000 Michigan workers is disturbing.  The GM / UAW study of workers exposed to machining fluids and some other studies done in the U.S. and Europe found excess levels of these kinds of cancers: Skin cancer, cancer of the larynx, cancer of the rectum, stomach cancer, cancer of the esophagus, colon cancer, bladder cancer, sinonasal cancer, lung cancer, prostate cancer, and cancer of the pancreas.

Lung Disease

U.S. studies of workers exposed to metalworking fluids have found increased numbers of asthma, bronchitis, lipid pneumonia, hypersensitivity pneumonitis (extrinsic allergic alveolitis) and fibrosis.  By measuring workers' ability to breathe at the beginning of the work shift compared to the end of the work shift, researchers in the U.S. found that workers exposed to quite small amounts of metalworking fluids had a reduced ability to breathe.

Safety Measures

Check the labels of the metalworking fluids used so that you know the type of metalworking fluids. 

Read the MSDSs (Material Safety Data Sheets) so that you will know the ingredients of the metalworking fluids. You need to know about the additives as well as the fluid itself. These additives are used to prevent corrosion and bacteria build up. When bacteria grow in metalworking fluids, the fluids go bad and smell awful. Fungi also grows in metalworking fluids. Both fungi and bacteria can cause lung disease and cancer.

 Find out if the additives are nitrites or ethanolamine-type chemicals. These additives produce nitrosamines which cause cancer. Anytime you see the words "corrosion inhibitor" or know that metal has been treated or coated to prevent rust, be suspicious. Even though nitrites or ethanolamines may not be listed as an additive, they may be found in the corrosion inhibitor. Insist that a less harmful additive be substituted.

Find out if any substance that may be used to coat or treat the metal as a rust inhibitor contains nitrites. If the metalworking fluid you use contains ethanolamine and there is a coating of a nitrite containing corrosion inhibitor on the metal you are working on, they will combine to form nitrosamines. 

Report on a conference on hazards associated with metal working fluids.
"A symposium on the Industrial Metalworking Environment: Assessment and Control" 
Nov 13-16, 1995 
Sponsored by:
The American Automobile Manufacturers Association (AAMA)
Occupational Safety and Health Administration (OSHA)
The National Institute of Occupational Safety and Health
United Automobile Workers (UAW)
and fourteen other organizations. 

The results have been reported as follows: 

"It is well known that prolonged or repeated contact with Metalworking fluids can cause contact dermatitis, or skin irritation. Less well known are the general effects of metalworking fluids on operator health."

"Furthermore, representatives agreed that the severity of the distress depended not only on the levels of bacteria and endotoxins in the fluid, but also on the amount of particulate matter in the fluid and the amount of exposure to and control of mists. The implication of all these findings is that bacterial populations need to be closely controlled and that filtration is as important now as it has ever been." 

"It is equally important that manufacturers take steps to minimize contamination of metalworking fluids with tramp oils, abrasive materials, and metal fines."

In other words, an OSHA sponsored conference concluded that filtering is as important now as it ever was and that elimination of abrasive materials and metal fines from grinding machine coolant is "important.”"

Skin irritation from metalworking fluids typically comes from the skin drying because of the detergent action of the machine coolant. The problem gets worse as concentration levels get higher. Contaminants in the machine coolant such as lubricating and hydraulic oils, abrasive particles, metal fines, dissolved metals (especially nickel, chromium, and cobalt), acids, and salts also increase the potential for damage. 

Epidemiology
One study seemed to indicate that exposure to metalworking fluids results in an increased risk of esophageal, pancreatic, and rectal cancers, especially among grinder operators. Another study done at foundries and engine plants showed increases in stomach and lung cancers, but the cancers did not seem attributable to metalworking fluids exposure. Questions about these studies were raised because of the many outside variables (e.g., smoking, diet influences, ethnic origin) that were not considered and the incomplete work histories of the subjects. Further complicating the epidemiological studies was the fact that machine coolants used when the data were gathered had different formulations from those used today. 

Toxicology
Alkanolamine manufacturers maintained that their research indicates alkanolamines are safe, but the UAW expressed strong concerns about them. The results of studies presented were largely inconclusive. Additional research was requested.  

The biocides used in metalworking fluids are the most studied and regulated ingredients in these fluids. Their toxicological profiles should certainly be considered as primary sources of information in selecting biocides for these applications. But the end user should select biocides in conjunction with the fluid supplier to assure compatibility of the biocides and the fluids.  

The Triazine Consortium, composed of the manufacturers and marketers of triazine biocides, discussed the results of studies it commissioned on the relationship between triazine - biocide use and formaldehyde exposure in the workplace. The conclusion was that triazine biocides do not release detectable levels of formaldehyde and are safe metalworking fluids components.  

Ann Ball of Cincinnati Milacron suggested that, based on her studies, a PEL of 2 Mg/M3 to 10 Mg/M3 would not cause pulmonary irritation in workers. While the research was well documented, there is reason to believe that PELs below which respiratory irritation will not be experienced will vary significantly according to the composition of the fluid, and it may be difficult to set one PEL for all types of fluids. Further studies are needed.  

Two other presenters, Dr. Don Milton of Harvard University and Dr. Peter Thorne of the University of Iowa, dealt with the role of bacteria and their growth byproducts (endotoxins) in causing respiratory distress among workers exposed to metalworking fluids mists. It was concluded that virgin fluid produced less distress and irritation than did used fluid. Furthermore, representatives agreed that the severity of the distress depended not only on the levels of bacteria and endotoxins in the fluid, but also on the amount of particulate matter in the fluid and the amount of exposure to and control of mists. The implication of all these findings is that bacterial populations need to be closely controlled and that filtration is as important now as it ever has been. 

Cobalt Safety & Health - Cobalt Leaching
As a binder in HSS and carbide tools, nothing beats cobalt. No other material imparts the toughness of cobalt to the tool while providing a uniform latticework of support for the hard, wear-resistant cutting grains. The cobalt that escapes the tool is another matter. When workers repeatedly come in contact with this free-floating cobalt, released into the shop's air and machine coolant while the tool is being made or sharpened, they suffer a host of medical problems. 

In researching the problem of cobalt exposure, experts in the fields of chemistry and metallurgy have tried to discover how the cobalt is freed from the tool matrix. Some is released as dust during grinding and cutting operations, but researchers also have found that some is leached by many of the amino alcohols and amine-base additives found in almost all water-miscible machining fluids. The mechanism by which amines leach cobalt is uncertain. One possibility is that the amines chelate cobalt, a process by which the amine molecules chemically link up with the cobalt atoms to form a water-soluble complex. This happens most frequently as carbide is being ground.

It can also happen when carbide tools come in contact with the machining fluid as they are being used. 

When regularly exposed to fluids with amino alcohol, tungsten carbide tooling will lose the cobalt needed to hold it together. The cobalt leached out by the amines eventually winds up as a contaminant in the Metalworking fluid itself, causing performance, health and environmental concerns. 

In the case of Hardmetal machining, cobalt leaching can be controlled by adding inhibitors to the fluid, such as triazoles. While this is effective initially, the inhibitor becomes depleted as the fluid is used and loses its effectiveness. However, inhibitors do little to control cobalt leaching during the manufacture of tungsten carbide tools, and during carbide grinding, where metal fines are a problem.  

Cobalt leaching is at the heart of three potentially costly problems. First, it reduces the performance and life of the tool. Next, cobalt is believed to be responsible for health problems in some workers, causing dermatitis in handling the fluid and respiratory distress from contaminated machine coolant mist. Finally, wastewater disposal may become a serious matter if cobalt levels in used fluids exceed the regulatory limit for heavy metals. 

Since learning how cobalt is leached from cemented carbide, researchers have been searching for ways to prevent the chemical reaction from taking place. They've enjoyed some success by adding a chemical barrier to the machine coolant that keeps the amines from attacking the cobalt. But the most effective solution appears to be a machine coolant formulated with amines that don't have such a strong affinity for cobalt.  

The Trouble With Cobalt
Modern machining practices have made it especially important to find a low-leaching machine coolant. Economic and environmental pressures have forced toolmakers and tool users to use machining fluids and fluid-handling systems that permit machine coolants and lubricants to be recirculated many times. Extending fluid life significantly lowers costs by reducing the number of times workers must shut down the line to change fluid and by minimizing the amount of fluid the workers must throw out and replace. However, the longer the fluid is used, the more opportunities the amines in the fluid have to grab cobalt out of the carbides that are being machined. Over time, the cobalt in the fluid reaches hazardous levels. 

As the cobalt content in the fluid rises, so do the health risks to the workers. Cobalt dust in a shop's air is known to cause respiratory and skin problems, and it is reasonable to suspect that the cobalt dissolved in the machining fluid will have many of the same effects. Cobalt-contaminated fluid causes dermatitis on skin that comes in contact with it. 

Workers also may suffer respiratory problems if they inhale contaminated machine coolant mist. 

Contaminated fluid also poses risks to the environment, and because of these risks, shops may find it more difficult and expensive to dispose of cobalt-tainted machine coolant. Although federal regulations do not single out cobalt, there are regulatory limits on the amount of heavy metals a company's effluent can contain. Should cobalt levels in a shop's wastewater rise above these limits, federal regulators may require the shop to treat the water as hazardous waste. 

Cobalt leaching is hazardous to carbide tools, as well. When the tool loses its binder, the surface is weakened and may be subject to accelerated wear. Also, the weakened surface structure will compromise the bond between the tool and any coating applied to it.  

Industry Response
Producers of Metalworking fluids have tried to block the amine/cobalt reaction with inhibitors such as benzozole and tolyltriazole. The inhibitors are believed to react with the cobalt on the surface of the tool before the amines have a chance to react with the cobalt and draw it out of the tool.  

Leaching inhibitors do work. However, once an inhibiting molecule reacts with the cobalt, it is no longer available for further reactions as the machining process exposes more cobalt. Eventually, the inhibitor is depleted, leaving any cobalt exposed beyond this point vulnerable to attack from the amines in the fluid.  

This explains the typical performance of a metalworking fluid that contains both cobalt-leaching amines and a leaching inhibitor. At first, the cobalt level in the fluid remains low. But over time, leaching causes the level to reach that found in an uninhibited fluid. The inhibitor may extend the life of the fluid, but the cobalt contamination will still force the operator to replace the fluid before it would have to be replaced if no leaching occurred. 

As an alternative, the operator can add fresh inhibitor, but this has its drawbacks as well. It's difficult to predict when cobalt contamination will reach dangerous levels. As a result, the operator must regularly monitor the cobalt level to determine when more inhibitor is required. The extra inhibitor also adds to the shop's machine coolant costs; in a typical case, the shop will spend about $5 per 100 gal. of machine coolant used for one tank side treatment.  

The easiest solution would be to eliminate the amines from the metalworking fluid altogether. Unfortunately, this is not always possible, because the amines perform vital functions better than any other substance. During fluid formulation, amines are used as corrosion inhibitors and emulsifiers both in their unreacted state and as key components in fluid additives. All amines added to the solution during the formulation of a metalworking fluid remain in the product.  

The industry has tried to find substitutes to take the place of amines in metalworking fluid, but these replacements have their own drawbacks. The only substances that approach the performance of the original amines are inorganic substances such as potassium hydroxide, but they are not as effective as amines in controlling fluid pH and ferrous-metal corrosion. These replacements also are extremely caustic. Prolonged contact can chemically burn a worker's skin. 

The Right Amine
Fortunately, researchers have found that they don't have to eliminate amines completely to reduce a Metalworking fluid's cobalt-leaching tendency. Fluid formulators seeking a rust inhibitor or emulsifier for their products have a number of amines to choose from, and these substances vary widely in their tendency to leach cobalt. 

One study compared the cobalt-dissolving tendencies of different amines when mixed with water in a 1% solution. Deionized water containing no amines also was tested and compared to the results of the amine-containing solutions. 

At the conclusion of the test, the solution with the highest-leaching amine had 10 times more cobalt in the fluid than the solution with the lowest leaching amine. For this study, the researchers used methods designed to replicate real-world results. The screening test they used to determine the amount of cobalt in the water and the different solutions is known to correlate with results in carbide tool manufacturing plants. During this test, water or one of the solutions was placed in a jar with swarf from an actual carbide grinding operation. The cobalt concentration in all the swarf samples was adjusted to yield 1500-ppm total cobalt based on the weight of the test solution. The mixture of swarf and water or solution was then vigorously mixed on a jar roller for 5 days. At the end of this period, the water or solution was filtered and atomic absorption was used to measure the amount of dissolved cobalt in the filtrate.  

As might be expected, deionized water leached the least cobalt. Straight water usually is not a suitable machining fluid, however, because it can corrode work pieces and lacks lubricity. The researchers found that the solution with the amine AMP-95 most closely matched the performance of deionized water containing no amines. At the conclusion of the test, the concentration of cobalt in the deionized water was 14 ppm; the concentration in the solution with AMP-95 was 23 ppm. Dissolved cobalt levels for the other solutions were 116 ppm for monoethanolamine, 198 ppm for mixed isopropanolamines, and 241 ppm for triethanolamine.  

Safety machine coolants
There seem to be many sales people in the market selling machine coolants that will not dissolve cobalt. Some of them are wrong and their machine coolants actually dissolve more cobalt. Some of them are partially right and their machine coolants dissolve cobalt more slowly than other machine coolants. We do not know of any machine coolant that truly does not dissolve any cobalt, ever.

Most machine coolant is basic because cobalt dissolves in acids better than bases. However Cobalt does dissolve in bases (also called caustic solutions). It just dissolves more slowly. 

The Materials Handbook says “cobalt...is dissolved by dilute sulfuric, nitric, or hydrochloric acids and is attacked slowly by alkalis”.

Webster’s Dictionary
“Alkalis”1. Any base or hydroxide 2.any substance than can neutralize acids, with a pH greater than 7.0.Strong alkalis are caustic.”

7.0 is a neutral pH. It is neither acidic nor basic (caustic). A pH below 7.0 is acid. A pH above 7.0 is basic. In our analyses of most machine coolants they show a pH that is slightly basic. Usually slightly above 8.0. 

Dr. Susan Kennedy of the University of British Columbia has tested various machine coolants. In her opinion some of the machine coolants sold as safety machine coolants are actually worse than non-safety machine coolants. In other words some machine coolants are sold with the claim that they dissolve less machine coolant and they dissolve more machine coolant. 

Chemical reaction
There is a chemical process called chelation. Chelation is: 1. A chemical compound in which the central atom (usually a metal ion) is attached to neighboring atoms by at least two coordinate bonds in such a way as to form a closed chain. or 2. To cause (a metal ion) to react with another molecule to form a chelate. 

Dissolving would mean that the Cobalt would break up into individual cobalt molecules in the water. Chelation means that it forms unique chemical compounds. This chelation is where we get the reddish or purplish coloration.  

Bacteria

Bacteria break complex substances such as sugar down into things like alcohol. They also break the chemicals in grinding machine coolants down into other things and they will use
 

Cobalt as part of the process.

The bacteria grow well for several reasons. First, they grow well in the undisturbed sludge and particles in the bottom of the sump. Second, they are anaerobic (do not need air) and grow well under water. Third, they feed on the substances in some grinding machine coolants. Fourth. They really like the tramp oils. Fifth, the tramp oils seal the top of the water so that no possible air gets to the bacteria. 

Water contains oxygen in two ways. Water has oxygen as part of its chemical make up as H₂O.Water also contains dissolved oxygen. (Boiled water tastes flat because the dissolved oxygen has been boiled out. The Boy Scout Handbook says to pour the water from one bucket to another to get oxygen back in which will make it taste better.) Dissolved oxygen also helps prevent the growth of anaerobic bacteria.

Filtering helps: 
1.Removes the particles before they can either dissolve or chelate or react other wise in the machine coolant. 
2.Removes the sludge and particulate that provide a nesting bed for bacteria in the bottom of the sump.
3.Removes the bacteria. 
4.Removes the oils that the bacteria eat. 
5.Aerates the mixture to help keep the oxygen content high so that the bacteria cannot grow. 

Studies on human health and inhaled machine coolants
Dr. Susan Kennedy at the University of British Columbia had done a survey of sawmill filing rooms. Her research seemed to show that there was a lot more danger in cobalt from tungsten carbide tools than anyone had realized. Breathing grinding machine coolant with dissolved cobalt is a real danger. Filtering the cobalt out of the machine coolant before it dissolves helps lessen that danger.

Breathing grinding machine coolant with chunks of wheel and carbide in it causes problems at least five ways. 

1.The machine coolant alone causes problems. It can cause a rash like dishpan hands. If you breathe in the mists then you can get these rashes in your throat and lungs. 

2.Size 
The human breathing system starts at the nose, which has nostrils about a quarter inch across. The respiratory system branches and splits and rebranches until you get down into the smallest part of part of the lungs, which handles air molecules that are about one ten billionth of an inch across. If you have grinding particles that are about one ten millionth of an inch across they are going to be able to get pretty far into the lungs. These big particles block the lungs like a basketball dropped into fish net.

 3.These particles are sharp.
The particles are typically rough chunks of tungsten carbide, diamond or cubic boron nitride. They are designed to have rough edges. The particles in grinding machine coolant get recirculated when the machine coolant is recirculated. These little, sharp particles can get inhaled and plug up your lungs as well as cutting and scarring lungs. The lungs are very soft and moist so that air molecules can pass through them. The rough chinks of material tear up the soft lung tissue causing scarring and loss of function. Breathing these rough chunks is like putting broken glass between your lip and your gums. Washington State Department of Ecology explains that anything below 10 microns in size will get into your lungs and lodge in the holes really well. About 59% of the billions and billions of particles in grinding machine coolant are at or under 10 microns in size. 

4.Allergic reactions
machine coolants dissolve metals. The dissolved metals can cause allergic reactions and scarring in your lungs, which gradually causes of loss of lung function. It appears that there is an allergic reaction to cobalt that differs from person to person. As with all allergic reactions the effect is much greater with some people than others. Some people die from bee stings but most people do not. However a bee sting hurts almost everyone. It seems to be a similar thing with cobalt. Cobalt affects some people much more than others but it is not a good thing for anyone.

5.Bacteria grow in machine coolant. They make it smell bad and they are a health hazard. Filtering removes the sludge that bacteria use to breed as well as removing tramp oils that bacteria eat and filtering keeps oxygen in the water. These are anaerobic bacteria, which means “non-oxygen” or non- air. They do not like air so keeping the machine coolant aerated helps prevent their growth.  

Basic housekeeping
If you run machine coolant through a clean filter you can remove up to 90% of all cobalt. 

Do not splash grinding machine coolant any harder or farther than you have to. What happens is that grinding machine coolant gets sprayed onto the work as a liquid then the splashing breaks the liquid up into really small drops (aerosols) and this is what you breathe. 

Keep the machine coolant away from the operator. Screens, shields, air intakes and cabinets can all be used to collect mist and prevent it from getting to an operator. 

There are lots of other material in grinding machine coolant. There are bits of diamond or CBN from the wheel, there is resin from the wheel and chunks of broken carbide as well as just general grit and dirt. We found that there could be up to 75,000,000 or 80,000,000 pieces of crud in a cubic centimeter. This would be 150,000,000,000 (150 billion) particles in a two-liter soda pop bottle. Filtering can get out over 99% of these particles.

Grinding fumes and dust can be dangerous. Inhaling grinding machine coolant, whether it is clean or dirty, can be dangerous. 

How dangerous it is depends on how much is inhaled, how long it is inhaled and who inhales it. 

Lungs
Your lungs look like two sacks. The left side has two lobes and the right side has three lobes. Each lobe gets divided into thousands of little passageways. Each passageway has thousands and thousands of little rooms going off of it. 

The air gets into these little rooms and gets trapped there when you exhale. The blood is rushing past these little rooms on the outside and the air is on the inside. The rushing blood sucks the air through the walls when you inhale and pushes the carbon dioxide out into the room when you exhale. 

You damage your lungs several ways. One way it to fill these rooms with crud so the air cannot get in or out. Small particles get carried down into these rooms and fill them up. So does the tar in cigarettes. The oxygen gets from your lungs to your blood only through these little rooms. The more of them that are blocked up the less oxygen you can get into your blood. If it gets bad enough you can start plugging up passageways and shutting down corridors and whole sections of lung. 

Another way to damage your lungs is to cut them up and then let scars form where the cuts were. The scars in your lungs are like the scars on your hands. It is different than ordinary skin. It does not breathe. Every time you scar lung tissue you lose some lung capacity. If you scar enough tissue then you die from slow strangulation.

Cadmium, chrome and cobalt
Basically you do not want to eat or drink either cobalt or nickel. Cobalt and nickel are everywhere and your body can handle a little of each but generally the less you breathe or eat the better. An argument about which is more dangerous is sort of like arguing about whether it is better to get hit by a school bus or a cement truck. The real answer is to avoid both.  Here are WISHA (Washington Industrial Safety and Health Act) and OSHA (Federal occupational Safety and Health Act) permissible exposure limits in mg/cu.m (milligrams per cubic meter) 

The real answer is to do as many are doing and set a limit of 100 ppm (parts per million) or 100 mg/L, or whatever else your expert recommends, for cobalt in machine coolant and then safely dispose of it at that level. That is really low by legal limits but it is safe and that should be important to you and I because it is our lungs we are talking about. 

Papers and Experts on Dangers of Cobalt
Here are some of the sources for information. Most of them are written well enough that you can pick out some information even without a lot of technical background.  

1. Maintenance of Stellite and Tungsten Carbide Saw Tips: Determinants of Exposure to Cobalt and Chromium
Dr. Susan Kennedy et.al.
University of British Columbia.
Journal of the American Industrial Hygiene Association (56) July 1995  

2. Toxicological Profile for Cobalt
US Dept. of Health & Human Services
Public Health Agency
Agency for Toxic Substances and Disease Registry Report # TP-91/10 

3. Industrial Exposure and Control Technologies for OSHA Regulated Hazardous Substances
US Dept of Labor
March 1989
Volume 1 of 2 Substances A-1 Cobalt (CAS Number 7440-48-4) 

4. Agency for Toxic Substances and Disease Registry
US Dept. of Health & Human Services
Public Health Service Cobalt 1048.01 

5. The Respiratory Effects of Cobalt
David W. Cugell, M.D. et. al.
In Archives of Internal Medicine Vol. 150 January 1990
Request reprints:
University Hospital 339 Windermere Rd. London, Ontario Canada N6A 5A5 (Dr. Morgan) 

6.Criteria for Controlling Occupational Exposure to Cobalt
US Dept. of Health & Human Services
Public Health Service
Center for Disease Control  October 1981
For sale by Supt. of Documents, Washington DC

7.Cobalt in Hardmetal Manufacturing Dusts
Matti Koponen, et. al.
American Industrial hygiene Journal (43) 9/82 

8. Exposure to Airborne Metals in the Manufacture and Maintenance of Hard Metal and Stellite Blades
Markku Linnainmaa, et. Al.
American Industrial Hygiene Association Journal (57) February 1996