Brazing Tungsten Carbide - Health and Safety

From the book Building Superior Brazed Tools    Buy the Book 

Contents

1. Standard Procedures
2. Possible Damage
3. “Safe” Braze Alloys Can Still Be Dangerous
4. Protecting the employee
5. Sources for Health Information

Introduction

I am not a medical doctor and I do not represent myself as an expert in these areas.  I believe this information to be true and accurate but I do not guarantee it.  There can be different standards in different localities and standards change all the time.  Think of this as background information.  If the issue is important then contact an expert listed, your company safety officer, someone with your state or local government, someone from a local university or any other expert.  You can also get more information on many of the Tool Materials listed in our Tool Tipping Materials Index 

Standard Procedures

The standard brazing operation for tungsten carbides exposes the brazing employee to a minimum of six substances rated at least as “very high” health risks and causes damage to kidneys, lungs, eyes, liver, digestive tract, and to various body parts, especially the bone structure in the form of cancer. There is no “perhaps” involved - there are definite and serious health hazards. 

The standard brazing operation consists of a stick of silver solder (braze alloy) containing cadmium which is coated with a flux containing potassium salts of fluoride and Boron and an acetylene or natural gas torch with Oxygen, which is used to heat the cobalt-matrix tungsten carbide. 

The materials involved are tungsten, carbon, and cobalt in the tungsten carbide; silver, cadmium, zinc, copper, and nickel in the solder; and various fluorine, Boron and potassium compounds in the brazing flux. These are the compounds we know to exist and does not even attempt to establish the hundreds of other compounds possible because of various substances in the gases used to heat or that are added to the flux and about which there is no readily available information. 

The dangers of cadmium are fairly well publicized since it is very toxic and very readily identifiable. It is usually classed with arsenic for reasons having to do with its toxicity and with its chemical makeup. Less well known is that Boron, cobalt, fluorine, fluoridates, and fluorides are rated in the same “high” class as cadmium, while fluorine monoxide, which is a possible by-product, is rated as “very high.” 

Possible Damage

A man sitting with a stick of solder is exposed to damage of a permanent and irreversible nature. The early symptoms masquerade as a cold or headache, sometimes approaching flu-like symptoms such as an upset stomach and nausea, and in an advanced stage there are symptoms such as pain the back of the legs, leading to permanent crippling. The formation of a yellow ring on the neck of the teeth leading to total yellowing, continuing upper respiratory distress leading to emphysema, and chronic gastric distress (upset stomach) leading to severe liver and kidney damage are also symptomatic. 

A woman brazing with a stick of solder and a torch suffers all the same problems as a man, plus there is additional hazard. There have been studies done that indicate that there is a very real added risk of damage to the placenta in a pregnant woman. What has not been established is the damage to a pregnant woman who is not only being exposed to cadmium directly, but already has high levels of cadmium in her bloodstream from previous exposure as a cigarette smoker. There is no evidence that such increased exposure would be beneficial. 

If an employee smokes, his cadmium level is already high enough to cause health problems and there is every evidence that he should not be allowed to be exposed to this type of brazing to any extent for his own safety and to protect the employer from claims arising from the employee’s own actions - in this case, smoking cigarettes. 

An employee who drinks in any amount and brazes tungsten carbides in this manner (that is, with a torch) is at an increased risk, because he already suffers some liver and kidney damage from the alcohol. 

Women of any possible childbearing age are probably the best kept away from this type of brazing due to possible placenta damage. An employee who smokes cigarettes or drinks to any great extent had a high risk already and it would take consequently less to push him into a serious problem than it would someone who didn’t smoke cigarettes. 

There’s an additional problem with those who smoke while they work. They put the cigarette down and pick it up while they are using a stick of solder and a torch. Their hands are much closer to the flames than their noses so that there might be a safe level at the shirt collar, which is where standard testing equipment is attached (so as to be between the face and the fumes), but the levels will be much higher at their fingers. They pick up their cigarettes with their fingers, put them in their mouths in a lot of cases touching their mouths) and they’ve directly transmitted cadmium as a solid. 

Any employee who is exposed to this type of brazing should be checked regularly and information should be kept, so as to detect any unusual recurrent or stubborn symptoms of flu’s, colds, or upset stomach. 

I badly understated the cancer risks in the First Edition. I made the assumption that someone who smokes and drinks alcohol and brazed with torch was at increased risk. I originally advanced the argument that the risk increased such that if each item had had a separate hazard rating so that smoking was 5 and alcohol was 3 and torch brazing was 4 then they added to 12.  It appears that a more accurate description would be that they multiply so that 5x3x4 is 60. 

A Short Explanation

Brazing carbides can be hazardous or it can be safe depending on the operator.   Silver and silver solder with Cadmium create a danger only when they are overheated.  When the solder gets too hot some of the metals in them start to fume and then to boil.  These boiling metals create fumes just like boiling water creates steam.  These fumes can condense as a very fine powder just as steam condenses into water.  The fumes and the resulting powder are not dangerous unless they are allowed to enter the body. 

There are two principal ways they enter the body.  They can be breathed and they can be eaten.  Ventilation systems to remove the fumes from the workplace are simple, relatively cheap and very effective.  They must always be used and they must not be re-adjusted.  A very slight adjustment in a ventilation system can do a great deal of damage.  Every state has a department of Labor and Industries that will test the air and the individual worker and help the employer decide what kind of ventilation system is necessary if one is necessary at all. 

In addition there are a lot of different styles of respirators that are comfortable and very effective in filtering out hazardous fumes if they should be necessary.  They must be worn as directed and they must have the filters changed and be generally serviced by the operator as necessary. 

If one is brazing there can be dust collected on the hand and fingers so you should wash your hands before eating or smoking.  You should also keep your workplace clean, which is what a good operator does anyway.

The danger from brazing solder increases greatly as the material is heated past the designated operating temperatures.  The metals do begin to fume and create a hazard at lower temperatures.  This is where free testing from the state can be particularly valuable.  Generally speaking, if you braze properly then you will produce a better braze joint and you will be safe.  Sloppy brazing will produce poor quality work and create dangers for you and your co-workers through overheating the solder.  Do not overheat the solder.  If you have any doubts about how to braze, ask.  Your health and your job both depend on proper brazing.  

Lastly, the fumes created by over-heating solder do damage to the body similar to the damage caused by tobacco and alcohol.  Your employer will provide you with safety equipment as necessary and will give you all the training you need to braze safely.  If you braze improperly and combine that with alcohol and tobacco then you run a serious risk of doing yourself significant damage.  If you braze properly you will not increase your risk of illness. 

“Safe” Braze Alloys Can Still Be Dangerous

There are Cadmium free braze alloys being sold and people are referring to them as “safe” alloys. Alloys without Cadmium may be less dangerous than alloys with Cadmium but they are still not safe.  “Less dangerous” does not mean “safe” in braze alloys. 

Braze alloys with Cadmium are dangerous.  Cadmium causes cancer.  It also attacks your liver and kidneys.  Over the last ten years the federal government has dramatically increased regulations on Cadmium.  All the states have followed the federal government’s lead and many states have enacted regulations that considerably exceed federal standards.  

There are braze alloys that are being sold as “safe’ because they do not contain Cadmium.  There are two problems with this.  Some Cadmium-free alloys actually do contain Cadmium.  Even those alloys that do not contain Cadmium can still be dangerous.   

Some Cadmium free braze alloys may contain Cadmium.  Braze alloy standards are set by the American Welding Society (AWS) which specifies alloy percentages to one tenth of a percent (0.1%).   The AWS specifications allow trace contaminants to fifteen hundredths of a percent (0.15%).   An alloy can have 0.14% cadmium in it and still be technically a Cadmium free alloy.   However this will be enough Cadmium to concern the EPA.  

There are other dangers in braze alloys.   Most braze alloys for tungsten carbides are Silver, Copper, Zinc and Nickel with Cadmium, Manganese or Tin.   These metals can all be dangerous if they are inhaled.  In addition the fumes from the flux and the torch can also be dangerous. 

There are two main means of exposure.  The first is from pretinning and brazing.  In pretinning the part is heated up with a torch or an oven until the alloy flows across it.   It is very easy to overheat the braze alloy and vaporize the metal if you are using a torch or a “ceramic kiln” type oven.  There is a big problem with overheating the material.  When you overheat the material the metals start to vaporize and come out of it.   The torch flame, the flux fumes and the metals in the alloy and carbide can all be hazardous if handled improperly.   The second route of exposure is from the grinding operation.  Grinding parts, whether wet or dry, can create dusts and mist that can contain hazardous particles. 

When done properly, brazing and grinding can be safe.   The big secret is to keep the metals from getting inside people. 

One important point is cleanliness.  Wash your hands before eating or smoking a cigarette.   People who smoke while brazing are constantly putting dangerous materials inside their lungs.  The cigarettes are dangerous in themselves.  The cigarette also collects metals and contaminants that get passed into the mouth.  The brazers or grinders hands are close to the work and get contaminants on them, which then get passed onto the cigarette when they pick it up.  

Another essential point is proper ventilation.   If you wash your hands then you will probably not eat much contaminant.  The next step is to keep from breathing it.    A suction device at the brazing station or the grinding station can make a tremendous amount of difference.    There are several excellent devices on the market that collect the fumes just above the point of generation.  Smoke tests show that the efficiency is incredibly high.  These devices are inexpensive, small and easy to work around. 

Heating the parts

If only that amount of heat is used so that the solder will flow, then the health risk is greatly reduced. Since many brazing operations consist of the operator heating the tungsten carbide piece and then applying the solder-flux combination to a hot tip, the tungsten carbide must be at least hot enough to melt the solder. Most skilled operators can braze a tip a second or considerably faster with generally one to three taps of the flux-solder rod, yet it can take up to three seconds for the solder to melt completely across the same piece of tungsten carbide in a temperature-controlled oven. This extremely rapid melting indicates that the tungsten carbide piece is well above the melting point of the solder. An experienced operator will learn to judge by color when the tungsten carbide is the correct temperature to melt the solder rapidly but there is really no indication of having the tungsten carbide too hot. 

When judging temperature by eye, the Metalcaster’s Bible, under a chart headed “Judging the approximate temperature of an object in the dark by eye,” shows that full blood red is 1050°F, dull-cherry red is 1195°F; A light cherry is 1550°F, running into oranges, yellows, and then whites. The problem comes from judging an object in the uneven light of an oxyacetylene torch, which would tend to make the object lighter than it is.  The additional problem with judging the temperature of an object by eye is distinguishing full cherry or light cherry because everyone sees and understands colors a little differently.  No two tips are going to braze at exactly the same temperature because this is a method subject to many variables.  When too much heat is used, additional health hazards are created because the more heat used the more chance of the various compounds burning out and the more chance of them oxidizing, creating additional harmful substances.

Protecting the Employee

There are two methods of protecting the employee from the fumes that are generated. The first is a ducting system to pull the fumes away from the work so that the operator cannot inhale them. This system usually consists of a duct placed slightly over the work with a fan of sufficient force so that random breezes caused by drafts, doors, passing equipment, and people will not affect the much grater air flow into the duct. 

Particular attention should be paid here since a great many operators consider the duct a nuisance and will move it what they consider a slight distance out of their way so that they may work more efficiently. Any kind of rudimentary testing will rapidly establish the fact that there is a significant fall off in airflow for every inch moved. If the operator moves it a matter of a couple of inches, he has, in effect, all but negated the safety involved in having the ducting installed. The cost of installing such a system will depend on the number of work stations involved and the distance from the work station to the disposal point, since that will determine the amount of ducting required, and the amount and length of ducting will in turn influence the size of the fan required to move the fumes with sufficient force to provide safety. 

In some cases all that is needed is a standard bathroom exhaust fan and some flexible ducting such as dryer exhaust flex tubing. The fumes should be exhausted outside the building for the widest dispersal possible. Ideally they will be exhausted through the roof. 

There is also a method in use that consists of a box fan blowing across the tips as they are brazed. This may make sense if only a few tips are being done per day but it does turn the area in the shop down wind into a toxic waste dump and increases the health hazards for all employees while reducing it for only one. 

The second method is the oven-brazing method, whereby the tungsten carbide pieces are brazed in the ovens and the fumes are exhausted from the oven and away from the operator. The oven method is rapidly gaining popularity because it also allows for a much greater efficiency in production. The operators are able to process more tips more rapidly, and it permits the use of operators with a much lower skill level. Ducting of whatever sort for an oven may be arranged so that fume collection is done only when the door is open, without the airflow in the first method which serves a heat sink to significantly slow the speed of operation. 

One of the real problems in the use of ducting in torch brazing is that if the air flow is strong enough to do any good, it has also got to be strong enough to cause a waver or distortion in the torch flame and the flame is cooked so that it takes longer for it to heat the tip. 

The employee may further be protected by the use of cadmium-free solder. If the tungsten carbides are properly cleaned and prepared, the cadmium-free solder will actually give a bond with considerably greater bonding strength than a cadmium solder bond on an untreated or poorly treated tungsten carbide piece.  

Fluxes

This is different from the fluxes. The fluxes are designed to first liquefy and spread across and secondly to gas.  If one brazes properly, one will see a layer of black flux covering the finished work piece. 

What we should try to do is avoid too high temperatures and establish a brazing process precise enough so that we are not burning out the cadmium. When it gets hot enough to burn out the cadmium, it burns out the silver, and it burns out the cobalt, particularly if you’re using a torch. The number of compounds possible runs into the thousands. 

A lot of acetylaldehydes and other organic compounds simply have no known health effects associated with them because the research hasn’t been done, so that once they get into the body it’s tough to tell what damage they’re doing. We have to remember that these things are very, very deceptive. 

You consistently hear that if you get any piece of tungsten carbide hot enough and keep hitting it with a stick of solder, they’ll all braze. Some of the literature from some of the companies even says that silver solder (braze alloy) does not readily flow on tungsten carbide, it puddles. This is wrong. A well made piece of tungsten carbide will oxidize from day one just as a clean piece of steel will rust but if you take a good piece of tungsten carbide and clean it a little the tungsten carbide wets extremely readily and the solder flows across it beautifully. 

An employee who keeps heating the tip repeatedly hitting it with a stick of solder is: 1. Burning the tip and the solder creating additional health hazards; 2. Using a great deal more solder than is actually necessary (sometimes as much as 3 to 5 times the necessary solder); 3.  Disguising a defect in the surface of the tungsten carbide tip that will probably never be revealed since the tip will shatter when it spins out for no apparent reason. This problem is greatest where shims are used since the shim is cut to be the same size as the area being brazed. If there is a pocket where the solder doesn’t want to flow it won’t show up since the shim will act like a plate that’s been tack-welded over a defect. The same problem arises in automatic brazing processes where there is no inspection of the pre-tinned tip before it is brazed on the saw. 

The color of the brazed tip, if one is using a torch method, can give evidence of the quality of the braze. If the tip is properly prepared and there is no burning or contaminants introduced then the color of the silver solder (braze alloy) on the tip will be identical in color to the original silver solder (braze alloy). All you’re doing is melting the solder. If it is burned or altered or contaminated then the color that you’re getting can help identify the problems you’re having. If the tip is getting hot enough so that the cobalt is coming out then you get a blue-green color from the cobalt-tungsten. With cobalt from the tip and bromine from the potassium salts of bromine and fluoride in the flux you get a dark pink color. Copper from the solder and carbon from the tungsten carbide yields a yellow or dark green color from copper carbonate. Copper tungstate yields a light green color. Burning fluorine oxide yields an orange color starting out as brown gas turning into a red liquid and then into an orange solid. Nickel and bromine will yield a yellow-brown or yellow-green color. As the flux burns off it goes from black or very dark brown to a white substance. 

If you lightly wash the tip you can see a white or colorless substance which is a fairly normal product of the Potassium-Boron and Potassium-Fluorine reactions. If it gets hot enough the potassium will react with cobalt or carbon to produce a rose color. In properly prepared tips that are properly brazed, there should be no color change in the solder.  

Melting doesn’t affect the color of the solder. What does affect the color is burning the solder either by itself or in combination with some of the other substances. Anything such as a rose to red, green to light greens, or yellows, are indicative that nickel, silver, and even in some cases the cobalt has been burned. The tip that has gotten too hot will have a definite blue color. It’s a very pretty blue and it is cobalt blue. If the tips are washed after they’re brazed you can detect a difference in the wash water. There’s a process that enriches the surfaces of the tip with cobalt so that the wash water comes out with a blue tinge. In properly prepared tips, the water comes out pretty much a true gray or gray-brown from the unburned flux. 

Conclusion

There are very real and very great dangers in brazing tungsten carbides with silver solder (braze alloy) but they are controllable. 

1.   Use only tungsten carbide from a manufacturer who supplies clean tungsten carbides. The addition of a plating, coating, etc., increases the possibilities of health risks, generally reduces the bonding strength and adds to the cost of the tip. 

2.   Clean the tip with a solution designed to remove grease, dirt, etc., and to soften the oxide layer on the surface of the tip. A properly prepared tip from a manufacturer may not need this step but we do it anyway. 

3.   Do not overheat the tip. Heat the tip to the point where the solder flows evenly over the surface with one tap of a fluxed rod if you are using a torch or only until full flow has been achieved if you are using an oven. 

4.   Do not burn the solder. If there is any color change in the solder on the pre-tinned tip from the original solder color the solder has been burnt. Burning silver solder (braze alloy) creates severe hazards and reduces the strength of the material. 

5.   Do not breathe the fumes.  Do not permit any brazing activity to occur unless there is a suction system to vent the fumes out of the shop. The greatest hazards are associated with the lowest concentrations since the operator will be poisoned without any awareness of what is occurring. 

6.   Do not try to force the tip to braze or tin through the use of additional heat or by continuous heating and application of solder. If the tip is that dirty it should be cleaned again. 

Sources for Health Information

Industrial Toxicology

Hamilton and Hardy - Third Edition

(State of Washington - Department of Labor and Industries)

(Industrial Safety and Health Division) 

The Analytical Toxicology of Industrial Inorganic Poisons

Morris B. Jacobs, Ph.D. 

Occupational Diseases - A Guide to Their Recognition

Us Department Of Health, Education, and Welfare 

BORON COMPOUNDS

TOTAL HEALTH RISK = HIGH and therefore considered an industrial poison. Used in medicine as sodium borate, boric acid or borax, which is a common cleaner.  

Boron poisoning causes depression of the circulation, persistent vomiting and diarrhea, followed by profound shock and coma. The temp becomes sub-normal and a scarletina-form rash may cover the entire body.  

The careless use of borax as a skin cleaner should be discouraged. 

Boron Oxide - Total Health Risk = Animal experiments suggest relatively LOW.

Boron Trifluoride - (Synonym(s): boron fluoride), Colorless gas. Pungent, irritant odor.  

CADMIUM

Total Health Risk = The oral toxicity of Cadmium and its compounds is HIGH.  

Inhalation

The inhalation of fumes or dusts of Cadmium primarily affects the respiratory tract; the kidneys may also be affected. Even brief exposure to high concentrations may result in pulmonary edema and death.  

Inhalation of dust or fumes may cause dryness of the throat, cough, headache, a sense of constriction in the chest, shortness of breath (dyspnea) and vomiting. More severe exposure results in marked lung changes, with persistent cough, pain in the chest, severe dyspnea and prostration which may terminate fatally. X-ray changes are usually similar to those seen in broncho-pneumonia. The urine is frequently dark. These symptoms are usually delayed for some hours after exposure, and fatal concentrations may be breathed without sufficient discomfort to warn the workman to leave the exposure. A yellow discoloration of the teeth has been reported in workers exposed to Cadmium.  Cadmium oxide fumes can cause metal fume fever resembling that caused by zinc oxide fumes. 

Ingestion

When these materials are ingested, the irritant and emetic action is so violent that little of the Cadmium is absorbed and fatal poisoning does not as a rule ensue.  Ingestion of Cadmium results in a gastrointestinal type of poisoning resembling food poisoning in its symptoms.  

Cadmium Borotungstate - Yellow triclinic crystals.

Cadmium Fluoride - Cubic white crystals.  Total Health Risk is HIGH via oral route.

Cadmium Fluoborate - Acute toxicity data:

Cadmium Oxide - amorphous, brown crystals; Total Health Risk - HIGH via oral and inhalation routes.

Cadmium Oxide Fume - Total Health Risk is HIGH irritant via inhalation route. 

Harmful Effects

Local - Cadmium is an irritant to the respiratory tract. Prolonged exposure can cause anosmia and a yellow stain or ring that gradually appears in the necks of the teeth. Cadmium compounds are poorly absorbed from the intestinal tract, but relatively well absorbed by inhalation. Skin absorption appears negligible. Once absorbed Cadmium has a very long half-life and is retained in the kidney and liver. 

It has been shown that cadmium is a poison entirely analogous to arsenic and mercury. Cadmium melts at 320.9°C, a few degrees lower than lead.  In industry, cadmium poisoning usually occurs from the accidental absorption of cadmium fumes or dusts through the respiratory system. It seldom occurs by ingestion.  

Recently, solders containing in varying amounts with copper, lead, tin, zinc, and silver, especially silver solder (braze alloy)s, known to be widely used, have been a source of poisoning. Such hazards exist chiefly because of ignorance of the toxic potential of cadmium so that no precautions are taken. 

Industrial and experimental evidence shows cadmium to be one of the most hazardous metals. It has a significant vapor pressure at its melting point; a concentration of 5,000 times the safe limit vale can be produced. Freshly generated fumes of cadmium have been shown to be more acutely poisonous than “old” settled fumes that are inhaled as a dust.  

Systemic Effects – short term

Systemic - Acute toxicity is almost caused by inhalation of cadmium fumes or dust which is produced when cadmium is heated. There is generally a latent period of a few hours after exposure before symptoms develop. During the ensuing period, symptoms may appear progressively. The earliest symptom is slight irritation of the upper respiratory tract. This may be followed over the next few hours by cough, pain in the chest, sweating, and chills which resemble the symptoms of nonspecific upper respiratory infection. Eight to 24 hours following acute exposure severe pulmonary irritation may develop, with pain in the chest, dyspnea, cough, and generalized weakness. Dyspnea may become more pronounced as pulmonary edema develops. The mortality rate in acute cases is about 15%. Patients who survive may develop emphysema and corpulmonale; recovery can be prolonged. 

Systemic changes due to cadmium absorption include damage to the kidneys with proteinuria, anemia, and elevated sedimentation rate. Of these, proteinuria (low molecular weight) is the most typical. In advanced stages of the disease, these may be increased urinary excretion of amino acids, glucose, calcium, and phosphates. These changes may lead to the formation of renal calculi. If the exposure is discontinued, there is usually no progression of the kidney damage. Mild hypochromic anemia is another systemic condition sometimes found in chronic exposure to cadmium. 

It is established that intense exposures to cadmium oxide can cause fatal pulmonary edema. Repeated exposures may damage the kidneys, respiratory tract, and gastrointestinal tract, including the liver.  Old and new reports suggest cadmium can cause changes in the skeleton and changes in the teeth. Piscator is of the opinion that changes in calcium metabolism are secondary to cadmium induced renal damage.  

Chronic Effects – Long term

Chronic cadmium poisoning has been reported after prolonged exposure to cadmium oxide fumes, cadmium oxide dust, cadmium sulfides, and cadmium stearates. Heavy smoking has been reported to considerably increase tissue Cadmium levels. In some cases, only the respiratory tract is affected. In others, the effects may be systemic due to absorption of the cadmium. Lung damage often results in a characteristic form of emphysema which in some instances is not preceded by a history of chronic bronchitis or coughing. This type of emphysema can be extremely disabling. Some studies have not shown these effects. 

In studies with experimental animals, cadmium has produced damage to the liver and central nervous system, testicular atrophy, teratogenic effects in rodents after intravenous injection of cadmium, decrease in total red cells, sarcomata, and testicular neoplasms. Hypertensive effects have also been produced. None of these conditions, however, has been found in man resulting from occupational exposure to cadmium. Heavy smoking would appear to increase the risk of cumulative toxic effects. 

Control of Toxic Effects

Cadmium should not be used where it may contaminate food or drink. 

Because of cadmium retention in the body, these presently used levels may not protect from harmful effects arising from long-term exposure. Elkins published air data associated with illness confirming the relationship between exposure and toxic effect as well as the value of engineering controls. Urinary cadmium levels reflect absorption but do not correlate with disease of intensity of exposure. 

Personal Protective Methods

Most important is the requirement that each worker be adequately protected by the use of effective respiratory protection: Either by dust masks, vapor canister respirators, or supplied air respirators. Clothing should be changed after each shift and clean work clothing issued each day. Food should not be eaten in contaminated work areas. Workers should shower after each shift before changing to street clothes.  

COBALT

The toxicology of cobalt from an industrial hygiene point of view has been reviewed by Fairhall. The use of cobalt industrially has increased within the past decade, principally in Stellite-, tungsten carbide-, and Alnico-type alloys. It is also used as bonding material in the preparation of tungsten carbide. While the toxicity of cobalt by mouth is low - indeed it has been shown that cobalt is a micronutrient, particularly for sheep and cattle - cobalt salts have been shown to cause polycythemia in animals, and powdered cobalt produces dermatitis. 

Cobalt Compounds

Total Health Risk = Experiments show that the toxicity of Co by mouth is LOW. In animals, administration of cobalt salts produces polycythemia. In humans, a single case of poisoning, liver and kidney damage has been attributed to cobalt. Locally, Co has been shown to produce dermatitis and certain investigators have been able to demonstrate a hypersensitivity of the skin to Co. There have also been reports of hematologic, digestive, and pulmonary changes in humans. It is a suspected carcinogen of the connective tissue and lungs. 

Cobalt Fluoborate II - Total Health Risk = HIGH via oral and inhalation routes. 

Cobaltic Fluoride - Hexagonal brown crystals.

Cobaltic Hydroxide - Black-brown powder.

Cobaltic Oxide - Black-gray powder.

Cobalt Monoboride - Prisms.

Cobaltous Fluoride - Monoclinic, rose-red crystals.

Cobaltous Oxide - (cobalt oxide) - Cubic green-brown crystals - Total Health Risk = MOD via oral and inhalation routes. An experimental carcinogen.  

FLUORIDES

Total Health Risk = HIGH irritant to skim, eyes, mucous membranes, via oral and inhalation routes.

Fluorides may occur in industrial processes as dusts, fumes, and vapors. 

A most powerful caustic irritant.  Inorganic fluorides are generally highly irritant and toxic. Acute effects resulting from exposure to fluorine compounds are due to hydrogen fluoride. Large doses can cause very severe nausea, vomiting, diarrhea, abdominal burning and cramp-like pains.  Can cause or aggravate attacks of asthma. Can cause severe bone changes, making normal movements painful. Some signs of pulmonary fibrosis are noted. Some enzyme systems effects are reported. An irritant to the eyes, skin and mucous membranes.  Also loss of weight, anorexia, anemia, wasting and cachexia, and dental defects are among the common findings in chronic fluorine poisoning. There may be an eosinophilia, and impairment of growth in young workers. Symptoms of intoxication include gastric, intestinal, circulatory, respiratory and nervous complaints and skin rashes. Organic fluorides are generally less toxic than other halogenated hydrocarbons. Common air contaminants. 

Fluoroborates

Total Health Risk = HIGH irritant to skin, eyes and mucous membranes via oral and inhalation routes. See also fluorides and boron compounds. 

SILVER COMPOUNDS

Silver Acetylide, Silver Difluoride, Silver Fluoride, Silver Oxide

The absorption of silver compounds into the circulation and the subsequent deposition of the reduced silver in various tissues of the body may result in the production of a generalized grayish pigmentation of the skin and mucous membranes - a condition known as argyria.  

ZINC COMPOUNDS

Total Health Risk = Variable, generally of low toxicity.  Zinc is not inherently a toxic element. However, when heated, it evolves a fume of zinc oxide which, when inhaled fresh, can cause a disease known as “brass founders’ ague” or “brass chills.”  

Zinc is not a poison in the usual sense of the word. Pure zinc, in contrast to metals such as lead, arsenic, antimony, and cadmium, has virtually no poisonous qualities even if ingested in relatively large amounts. However, there are indications that continuous ingestion of soluble zinc compounds, for instance, swallowing zinc-bearing dusts with the saliva, may cause chronic gastritis with emesis. Certain zinc compounds are caustic. The one most commonly met in industry is, as was mentioned, zinc chloride. This is used as a glue in soldering, and if spattered may cause bad burns. Zinc sulfate is also caustic, while zinc chromate may cause dermatitis. Other zinc compounds are harmful because of their state of subdivision. This is the greatest single hazard to workers in zinc and zinc products. 

Metal-Fume Fever

 It was formerly thought that zinc metal was the cause of brass-founders’ ague, smelter shakes, and brass chills. The term “metal-fume fever” is now used to cover such affections. It has been shown that the chill and fever thought to be produced by zinc oxide alone can also occur when oxides of other metals are inhaled. Thus, it has been demonstrated that zinc stearate, copper oxide and magnesium oxide can also give rise to this type of illness. Koelsch concluded that metal-fume fever may occur from the inhalation of all heavy metals. Drinker and co-workers found that 45mg of zinc oxide, measured as zinc, per cubic meter of air could be inhaled for 20 min. without causing symptoms. They found that in a metallurgical plant, 14/mg/m3 produced no reaction in 8 hours. 

It is possible for people to become immune to it, but his immunity can be broken by cessation of exposure of only a few days. Zinc oxide dust which is not freshly formed is virtually innocuous. There is no cumulative effect to the inhalation of zinc fumes. Fatalities however have resulted from lung damage caused by the inhalation of high concentration of zinc chloride fumes.  

Exposure to zinc chloride fumes can cause damage to the mucous membranes of the nasopharnyx and respiratory tract and give rise to a pale gray cyanosis. Workers in zinc refining have been reported as suffering from a variety of non-specific intestinal, respiratory and nervous symptoms. Ulceration of the nasal septum and eczematous dermatosis are also reported. 

Zinc chloride, because of its caustic action, can cause ulceration of the fingers, hands and forearms of those who use it as a flux in soldering. It is the opinion of some who work with it that it is carcinogenic. Many Zinc salts are known or suspected carcinogens.  

Treatment and Antidotes: Personnel exposed to zinc chloride fumes should immediately wash the area of contact with copious quantities of warm water and soap. Remove all contaminated clothing at once and if the area of contact is large, subject patient to a deluge-type of shower a quickly as possible. If the eyes are involved in exposure to zinc chloride fumes, they should be irrigated for at least 15 min. with warm water.