Wednesday, 16 March 2011 22:01

Industrial Lubricants, Metal Working Fluids and Automotive Oils

Written by
Rate this item
(0 votes)

The industrial revolution could not have occurred without the development of refined petroleum-based industrial oils, lubricants, cutting oils and greases. Prior to the discovery in the 1860s that a superior lubricant could be produced by distilling crude oil in a vacuum, industry depended on naturally occurring oils and animal fats such as lard and whale sperm oil for lubricating moving parts. These oils and animal products were especially susceptible to melting, oxidation and breakdown from exposure to heat and moisture produced by the steam engines which powered almost all industrial equipment at that time. The evolution of petroleum-based refined products has continued from the first lubricant, which was used to tan leather, to modern synthetic oils and greases with longer service life, superior lubricating qualities and better resistance to change under varying temperatures and climatic conditions.

Industrial Lubricants

All moving parts on machinery and equipment require lubrication. Although lubrication may be provided by dry materials such as Teflon or graphite, which are used in parts such as small electrical motor bearings, oils and greases are the most commonly used lubricants. As the complexity of the machinery increases, the requirements for lubricants and metal process oils become more stringent. Lubricating oils now range from clear, very thin oils used to lubricate delicate instruments, to thick, tar-like oils used on large gears such as those which turn steel mills. Oils with very specific requirements are used both in the hydraulic systems and to lubricate large computer-operated machine tools such as those used in the aerospace industry to produce parts with extremely close tolerances. Synthetic oils, fluids and greases, and blends of synthetic and petroleum-based oils, are used where extended lubricant life is desired, such as sealed-for-life electric motors, where the increased time between oil changes offsets the difference in cost; where extended temperature and pressure ranges exist, such as in aerospace applications; or where it is difficult and expensive to re-apply the lubricant.

Industrial Oils

Industrial oils such as spindle and lubricating oils, gear lubricants, hydraulic and turbine oils and transmission fluids are designed to meet specific physical and chemical requirements and to operate without discernible change for extended periods under varying conditions. Lubricants for aerospace use must meet entirely new conditions, including cleanliness, durability, resistance to cosmic radiation and the ability to operate in extremely cold and hot temperatures, without gravity and in a vacuum.

Transmissions, turbines and hydraulic systems contain fluids which transfer force or power, reservoirs to hold the fluids, pumps to move the fluids from one place to another and auxiliary equipment such as valves, piping, coolers and filters. Hydraulic systems, transmissions and turbines require fluids with specific viscosities and chemical stability to operate smoothly and provide the controlled transfer of power. The characteristics of good hydraulic and turbine oils include a high viscosity index, thermal stability, long life in circulating systems, deposit resistance, high lubricity, anti-foam capabilities, rust protection and good demulsibility.

Gear lubricants are designed to form strong, tenacious films which provide lubrication between gears under extreme pressure. The characteristics of gear oils include good chemical stability, demulsibility and resistance to viscosity increase and deposit formation. Spindle oils are thin, extremely clean and clear oils with lubricity additives. The most important characteristics for way oils—used to lubricate two flat sliding surfaces where there is high pressure and slow speed—are lubricity and tackiness to resist squeezing out and resistance to extreme pressure.

Cylinder and compressor oils combine the characteristics of both industrial and automotive oils. They should resist accumulation of deposits, act as a heat transfer agent (internal combustion engine cylinders), provide lubrication for cylinders and pistons, provide a seal to resist blow-back pressure, have chemical and thermal stability (especially vacuum pump oil), have a high viscosity index and resist water wash (steam-operated cylinders) and detergency.

Automotive Engine Oils

Manufacturers of internal combustion engines and organizations, such as the Society of Automotive Engineers (SAE) in the United States and Canada, have established specific performance criteria for automotive engine oils. Automotive gasoline and diesel engine oils are subjected to a series of performance tests to determine their chemical and thermal stability, corrosion resistance, viscosity, wear protection, lubricity, detergency and high and low temperature performance. They are then classified according to a code system which allows consumers to determine their suitability for heavy-duty use and for different temperatures and viscosity ranges.

Oils for automotive engines, transmissions and gear cases are designed with high viscosity indexes to resist changes in viscosity with temperature changes. Automotive engine oils are especially formulated to resist breakdown under heat as they lubricate internal combustion engines. Internal combustion engine oils must not be too thick to lubricate the internal moving parts when an engine starts up in cold weather, and they must not thin out as the engine heats up when operating. They should resist carbon build-up on valves, rings and cylinders and the formation of corrosive acids or deposits from moisture. Automotive engine oils contain detergents designed to hold carbon and metallic wear particles in suspension so that they can be filtered out as the oil circulates and not accumulate on internal engine parts and cause damage.

Cutting Fluids

The three types of cutting fluids used in industry are mineral oils, soluble oils and synthetic fluids. Cutting oils are typically a blend of high-quality, high-stability mineral oils of various viscosities together with additives to provide specific characteristics depending on the type of material being machined and the work performed. Soluble water-in-oil cutting fluids are mineral oils (or synthetic oils) which contain emulsifiers and special additives including defoamants, rust inhibitors, detergents, bactericides and germicides. They are diluted with water in varying ratios before being used. Synthetic cutting fluids are solutions of non-petroleum-based fluids, additives and water, rather than emulsions, some of which are fire resistant for machining specific metals. Semi-synthetic fluids contain 10 to 15% mineral oil. Some special fluids have both lubricating oil and cutting fluid characteristics due to the tendency of fluids to leak and intermix in certain machine tools such as multi-spindle, automatic screw machines.

The desired characteristics of cutting fluids depend on the composition of the metal being worked on, the cutting tool being used and the type of cutting, planing or shaping operation performed. Cutting fluids improve and enhance the metal working process by cooling and lubrication (i.e., protecting the edge of the cutting tool). For example, when working on a soft metal which creates a lot of heat, cooling is the most important criterion. Improved cooling is provided by using a light oil (such as kerosene) or water-based cutting fluid. Control of the built-up edge on cutting tools is provided by anti-weld or anti-wear additives such as sulphur, chlorine or phosphorus compounds. Lubricity, which is important when working on steel to overcome the abrasiveness of iron sulphide, is provided by synthetic and animal fats or sulphurized sperm oil additives.

Other Metal Working and Process Oils

Grinding fluids are designed to provide cooling and prevent metal build-up on grinding wheels. Their characteristics include thermal and chemical stability, rust protection (soluble fluids), preventing gummy deposits upon evaporation and a safe flashpoint for the work performed.

Quench oils, which require high stability, are used in metal treating to control the change of the molecular structure of steel as it cools. Quenching in lighter oil is used to case harden small, inexpensive steel parts. A slower quench rate is used to produce machine tool steels which are fairly hard on the outside with lower internal stress. A gapped or multi-phase quenching oil is used to treat high carbon and alloy steels.

Roll oils are specially formulated mineral or soluble oils which lubricate and provide a smooth finish to metal, particularly aluminium, copper and brass, as it goes through hot and cold rolling mills. Release oils are used to coat dies and moulds to facilitate the release of the formed metal parts. Tanning oils are still used in the felt and leather-making industry. Transformer oils are specially formulated dielectric fluids used in transformers and large electric breakers and switches.

Heat transfer oils are used in open or closed systems and may last up to 15 years in service. The primary characteristics are good thermal stability as systems operate at temperatures from 150 to 315°C, oxidation stability and high flashpoint. Heat transfer oils are normally too viscous to be pumped at ambient temperatures and must be heated to provide fluidity.

Petroleum solvents are used to clean parts by spraying, dripping or dipping. The solvents remove oil and emulsify dirt and metal particles. Rust preventive oils may be either solvent or water based. They are applied to stainless steel coils, bearings and other parts by dipping or spraying, and leave polarized or wax films on the metal surfaces for fingerprint and rust protection and water displacement.

Greases

Greases are mixtures of fluids, thickeners and additives used to lubricate parts and equipment which cannot be made oil-tight, which are hard to reach or where leaking or splashed liquid lubricants might contaminate products or create a hazard. They have a wide range of applications and performance requirements, from lubricating jet engine bearings at sub-zero temperatures to hot rolling mill gears, and resisting acid or water washout, as well as the continuous friction created by railroad car wheel roller bearings.

Grease is made by the blending of metallic soaps (salts of long-chained fatty acids) into a lubricating oil medium at temperatures of 205 to 315°C. Synthetic greases may use di-esters, silicone or phosphoric esters and polyalkyl glycols as fluids. The characteristics of the grease depend to a great extent upon the particular fluid, metallic element (e.g., calcium, sodium, aluminium, lithium and so on) in the soap and the additives used to improve performance and stability and to reduce friction. These additives include extreme-pressure additives which coat the metal with a thin layer of non-corrosive metallic sulphur compounds, lead naphthenate or zinc dithiophosphate, rust inhibitors, anti-oxidants, fatty acids for added lubricity, tackiness additives, colour dyes for identification and water inhibitors. Some greases may contain graphite or molybdenum fillers which coat the metallic parts and provide lubrication after the grease has run out or decomposed.

Industrial Lubricants, Grease and Automotive Engine Oil Additives

In addition to using high-quality lubricant base stocks with chemical and thermal stability and high viscosity indexes, additives are needed to enhance the fluid and provide specific characteristics required in industrial lubricants, cutting fluids, greases and automotive engine oils. The most commonly used additives include but are not limited to the following:

  • Anti-oxidants. Oxidation inhibitors, such as 2,6-ditertiary butyl, paracresol and phenyl naphthylamine, reduce the rate of deterioration of oil by breaking up the long-chain molecules which form when exposed to oxygen. Oxidation inhibitors are used to coat metals such as copper, zinc and lead to prevent contact with the oil so they will not act as catalysts, speeding up oxidation and forming acids which attack other metals.
  • Foam inhibitors. Defoamants, such as silicones and polyorganic silioxanes, are used in hydraulic oils, gear oils, transmission fluids and turbine oils to reduce surface film tension and remove air entrapped in the oil by pumps and compressors, in order to maintain constant hydraulic pressure and prevent cavitation.
  • Corrosion inhibitors. Anti-rust additives, such as lead naphthenate and sodium sulphonate, are used to prevent rust from forming on metallic parts and systems where circulating oil has been contaminated with water or by moist air which entered system reservoirs as they cooled down when the equipment or machinery was not in use.
  • Anti-wear additives. Anti-wear additives, such as tricresylphosphate, form polar compounds which are attracted to metal surfaces and provide a physical layer of additional protection in the event that the oil film is not sufficient.
  • Viscosity index improvers. Viscosity index improvers help oils resist the effects of temperature changes. Unfortunately, their effectiveness diminishes with extended use. Synthetic oils are designed with very high viscosity indexes, allowing them to maintain their structure over wider temperature ranges and for much longer periods of time than mineral oils with viscosity index improver additives.
  • Demulsifiers. Water inhibitors and special compounds separate water out of oil and prevent gum formation; they contain waxy oils which provide added lubricity. They are used where equipment is subject to water wash or where a large amount of moisture is present, such as in steam cylinders, air compressors and gear cases contaminated by soluble cutting fluids.
  • Colour dyes. Dyes are used to assist users to identify different oils used for specific purposes, such as transmission fluids and gear oils, in order to prevent misapplication.
  • Extreme pressure additives. Extreme pressure additives, such as non-corrosive sulphurized fatty compounds, zinc dithiophosphate and lead naphthenate, are used in automotive, gear and transmission oils to form coatings which protect metal surfaces when the protective oil film thins or is squeezed out and cannot prevent metal to metal contact.
  • Detergents. Metal sulphonate and metal phenate detergents are used to hold dirt, carbon and metallic wear particles in suspension in hydraulic oils, gear oils, engine oils and transmission fluids. These contaminants are typically removed when the oil passes through a filter to prevent their being recirculated through the system where they could cause damage.
  • Tackiness additives. Adhesive or tackiness additives are used to enable oils to adhere to and resist leakage from bearing assemblies, gear cases, large open gears on mills and construction equipment, and overhead machinery. Their tackiness diminishes with extended service.
  • Emulsifiers. Fatty acids and fatty oils are used as emulsifiers in soluble oils to help form solutions with water.
  • Lubricity additives. Fat, lard, tallow, sperm and vegetable oils are used to provide a higher degree of oiliness in cutting oils and some gear oils.
  • Bactericides. Bactericides and germicides, such as phenol and pine oil, are added to soluble cutting oils to prolong the life of the fluid, maintain stability, reduce odours and prevent dermatitis.

 

Manufacturing Industrial Lubricants and Automotive Oils

Industrial lubricants and oils, grease, cutting fluids and automotive engine oils are manufactured in blending and packaging facilities, also called “lube plants” or “blending plants”. These facilities may be located either in or adjacent to refineries which produce lubricant base stocks, or they may be some distance away and receive the base stocks by marine tankers or barges, railroad tank cars or tank trucks. Blending and packaging plants blend and compound additives into lubricating oil base stocks to manufacture a wide range of finished products, which are then shipped in bulk or in containers.

The blending and compounding processes used to manufacture lubricants, fluids and greases depend on the age and sophistication of the facility, the equipment available, the types and formulation of the additives used and the variety and volume of products produced. Blending may require only physical mixing of base stocks and additive packages in a kettle using mixers, paddles or air agitation, or auxiliary heat from electric or steam coils may be needed to help dissolve and blend in the additives. Other industrial fluids and lubricants are produced automatically by mixing base stocks and pre-blended additive and oil slurries through manifold systems. Grease may be either batch produced or continuously compounded. Lube plants may compound their own additives from chemicals or purchase pre-packaged additives from specialty companies; a single plant may use both methods. When lube plants manufacture their own additives and additive packages, there may be a need for high temperatures and pressures in addition to chemical reactions and physical agitation to compound the chemicals and materials.

After production, fluids and lubricants may be held in the blending kettles or placed in holding tanks to ensure that the additives remain in suspension or solution, to allow time for testing to determine whether the product meets quality specifications and certification requirements, and to allow process temperatures to return to ambient levels before products are packaged and shipped. When testing is completed, finished products are released for bulk shipment or packaging into containers.

Finished products are shipped in bulk in railroad tank cars or in tank trucks directly to consumers, distributors or outside packaging plants. Finished products also are shipped to consumers and distributors in railroad box cars or package delivery trucks in a variety of containers, as follows:

  • Metal, plastic and combination metal/plastic or plastic/fibre intermediate bulk containers, which range in size from 227 l to approximately 2,840 l, are shipped as individual units on built-in or separate pallets, stacked 1 or 2 high.
  • Metal, fibre or plastic drums with a capacity of 208 l, 114 l or 180 kg are typically shipped 4 to a pallet.
  • Metal or plastic drums with a capacity of 60 l or 54 kg, and 19 l or 16 kg metal or plastic pails, are stacked on pallets and banded or stretch wrapped to maintain stability.
  • Metal or plastic containers with a capacity of 8 l or 4 l, 1 l plastic, metal and fibre bottles and cans and 2 kg grease cartridges are packaged in cartons which are stacked on pallets and banded or stretch wrapped for shipment.


Some blending and packaging plants may ship pallets of mixed products and mixed sizes of containers and packages directly to small consumers. For example, a single-pallet shipment to a service station could include 1 drum of transmission fluid, 2 kegs of grease, 8 cases of automotive engine oil and 4 pails of gear lubricant.

Product Quality

Lubricant product quality is important to keep machines and equipment operating properly and to produce quality parts and materials. Blending and packaging plants manufacture finished petroleum products to strict specifications and quality requirements. Users should maintain the level of quality by establishing safe practices for the handling, storage, dispensing and transfer of lubricants from their original containers or tanks to the dispensing equipment and to the point of application on the machine or equipment to be lubricated or the system to be filled. Some industrial facilities have installed centralized dispensing, lubrication and hydraulic systems which minimize contamination and exposure. Industrial oils, lubricants, cutting oils and grease will deteriorate from water or moisture contamination, exposure to excessively high or low temperatures, inadvertent mixing with other products and long-term storage which allows additive drop-out or chemical changes to occur.

Health and Safety

Because they are used and handled by consumers, finished industrial and automotive products must be relatively free of hazards. There is a potential for hazardous exposures when blending and compounding products, when handling additives, when using cutting fluids and when operating oil mist lubrication systems.

The chapter Oil and natural gas refineries in this Encyclopaedia gives information regarding potential hazards associated with auxiliary facilities at blending and packaging plants such as boiler rooms, laboratories, offices, oil-water separators and waste treatment facilities, marine docks, tank storage, warehouse operations, railroad tank car and tank truck loading racks and railroad box car and package truck loading and unloading facilities.

Safety

Manufacturing additives and slurries, batch compounding, batch blending and in-line blending operations require strict controls to maintain desired product quality and, along with the use of PPE, to minimize exposure to potentially hazardous chemicals and materials as well as contact with hot surfaces and steam. Additive drums and containers should be stored safely and kept tightly sealed until ready for use. Additives in drums and bags need to be handled properly to avoid muscular strain. Hazardous chemicals should be properly stored, and incompatible chemicals should not be stored where they can mix with one another. Precautions to be taken when operating filling and packaging machinery include using gloves and avoiding catching fingers in devices which crimp covers on kegs and pails. Machine guards and protective systems should not be removed, disconnected or by-passed to expedite work. Intermediate bulk containers and drums should be inspected before filling to make sure they are clean and suitable.

A confined-space permit system should be established for entry into storage tanks and blending kettles for cleaning, inspection, maintenance or repair. A lockout/tagout procedure should be established and implemented before working on packaging machinery, blending kettles with mixers, conveyors, palletizers and other equipment with moving parts.

Leaking drums and containers should be removed from the storage area and spills cleaned up to prevent slips and falls. Recycling, burning and disposal of waste, spilled and used lubricants, automotive engine oils and cutting fluids should be in accordance with government regulations and company procedures. Workers should use appropriate PPE when cleaning spills and handling used or waste products. Drained motor oil, cutting fluids or industrial lubricants which may be contaminated with gasoline and flammable solvents should be stored in a safe place away from sources of ignition, until proper disposal.

Fire protection

While the potential for fire is less in industrial and automotive lubricant blending and compounding than in refining processes, care must be taken when manufacturing metal working oils and greases due to the use of high blending and compounding temperatures and lower flashpoint products. Special precautions should be taken to prevent fires when products are dispensed or containers filled at temperatures above their flashpoints. When transferring flammable liquids from one container to another, proper bonding and grounding techniques should be applied to prevent static build-up and electrostatic discharge. Electrical motors and portable equipment should be properly classified for the hazards present in the area in which they are installed or used.

The potential for fire exists if a leaking product or vapour release in the lube blending and grease processing or storage areas reaches a source of ignition. The establishment and implementation of a hot-work permit system should be considered to prevent fires in blending and packaging facilities. Storage tanks installed inside buildings should be constructed, vented and protected in accordance with government requirements and company policy. Products stored on racks and in piles should not block fire protection systems, fire doors or exit routes.

Storage of finished products, both in bulk and in containers and packages, should be in accordance with recognized practices and fire prevention regulations. For example, flammable liquids and additives which are in solutions of flammable liquids may be stored in outside buildings or separate, specially designed inside or attached storage rooms. Many additives are stored in warm rooms (38 to 65°C) or in hot rooms (over 65°C) in order to keep the ingredients in suspension, to reduce the viscosity of thicker products or to provide for easier blending or compounding. These storage rooms should comply with electrical classification, drainage, ventilation and explosion venting requirements, especially when flammable liquids or combustible liquids are stored and dispensed at temperatures above their flashpoints.

Health

When blending, sampling and compounding, personal and respiratory protective equipment should be considered to prevent exposures to heat, steam, dusts, mists, vapours, fumes, metallic salts, chemicals and additives. Safe work practices, good hygiene and appropriate personal protection may be needed for exposure to oil mists, fumes and vapours, additives, noise and heat when conducting inspection and maintenance activities while sampling and handling hydrocarbons and additives during the production and packaging and when cleaning up spills and releases:

  • Work shoes with oil- or slip-resistant soles should be worn for general work, and approved protective toe safety shoes with oil- or slip-resistant soles should be worn where hazards of foot injuries from rolling or falling objects or equipment exist.
  • Safety goggles and respiratory protection may be needed for hazardous exposures to chemicals, dust or steam.
  • Impervious gloves, aprons, footwear, face shields and chemical goggles should be worn when handling hazardous chemicals, additives and caustic solutions and when cleaning up spills.
  • Head protection may be needed when working in pits or areas where the potential exists for injury to the head.
  • Ready access to appropriate cleaning and drying facilities to handle splashes and spills should be provided.

 

Oil is a common cause of dermatitis, which can be controlled through the use of PPE and good personal hygiene practices. Direct skin contact with any formulated greases or lubricants should be avoided. Lighter oils such as kerosene, solvents and spindle oils defat the skin and cause rashes. Thicker products, such as gear oils and greases, block the pores of the skin, leading to folliculitis.

Health hazards due to microbial contamination of oil may be summarized as follows:

  • Pre-existing skin conditions may be aggravated.
  • Lubricant aerosols of respirable size may cause respiratory illness.
  • Organisms may change the composition of the product so that it becomes directly injurious.
  • Harmful bacteria from animals, birds or humans may be introduced.

 

Contact dermatitis may occur when employees are exposed to cutting fluids during production, work or maintenance and when they wipe oil-covered hands with rags embedded with minute metal particles. The metal causes small lacerations in the skin which may become infected. Water-based cutting fluids on skin and clothing may contain bacteria and cause infections, and the emulsifiers may dissolve fats from the skin. Oil folliculitis is caused by prolonged exposure to oil-based cutting fluids, such as from wearing oil-soaked clothing. Employees should remove and launder clothing that is soaked with oil before wearing it again. Dermatitis may also be caused by using soaps, detergents or solvents to clean the skin. Dermatitis is best controlled by good hygiene practices and minimizing exposure. Medical advice should be sought when dermatitis persists.

In the extensive review conducted as a basis for its criteria document, the US National Institute for Occupational Safety and Health (NIOSH) found an association between exposure to metal working fluids and the risk of developing cancer at several organ sites, including the stomach, pancreas, larynx and rectum (NIOSH 1996). The specific formulations responsible for the elevated cancer risks remain to be determined.

Occupational exposure to oil mists and aerosols is associated with a variety of non-malignant respiratory effects, including lipoid pneumonia, asthma, acute airways irritation, chronic bronchitis and impaired pulmonary function (NIOSH 1996).

Metal working fluids are readily contaminated by bacteria and fungi. They may affect the skin or, when inhaled as contaminated aerosols, they may have systemic effects.

Refinery processes such as hydrofinishing and acid treatment are used to remove aromatics from industrial lubricants, and the use of naphthenic base stocks has been restricted in order to minimize carcinogenicity. Additives introduced in blending and compounding may also create a potential risk to health. Exposures to chlorinated compounds and leaded compounds, such as those used in some gear lubricants and greases, cause irritation of the skin and may be potentially hazardous. Tri-orthocresyl phosphate has caused outbreaks of nerve palsies when lubricating oil was accidentally used for cooking. Synthetic oils consist mainly of sodium nitrite and triethanolamine and additives. Commercial triethanolamine contains diethanolamine, which can react with sodium nitrite to form a relatively weak carcinogen, N-nitrosodiethanolamine, which may create a hazard. Semi-synthetic lubricants present the hazards of both products, as well as the additives in their formulations.

Product safety information is important to employees of both manufacturers and users of lubricants, oils and greases. Manufacturers should have material safety data sheets (MSDSs) or other product information available for all of the additives and base stocks used in blending and compounding. Many companies have conducted epidemiological and toxicological testing to determine the degree of hazards associated with any acute and chronic health effects of their products. This information should be available to workers and users through warning labels and product safety information.

 

Back

Read 8695 times Last modified on Tuesday, 28 June 2011 14:18

" DISCLAIMER: The ILO does not take responsibility for content presented on this web portal that is presented in any language other than English, which is the language used for the initial production and peer-review of original content. Certain statistics have not been updated since the production of the 4th edition of the Encyclopaedia (1998)."

Contents

Preface
Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Electrical Appliances and Equipment
Metal Processing and Metal Working Industry
Smelting and Refining Operations
Metal Processing and Metal Working
Microelectronics and Semiconductors
Glass, Pottery and Related Materials
Printing, Photography and Reproduction Industry
Woodworking
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides

Metal Processing and Metal Working Industry References

Buonicore, AJ and WT Davis (eds.). 1992. Air Pollution Engineering Manual. New York: Van Nostrand Reinhold/Air and Waste Management Association.

Environmental Protection Agency (EPA). 1995. Profile of the Nonferrous Metals Industry. EPA/310-R-95-010. Washington, DC: EPA.

International Association for Research on Cancer (IARC). 1984. Monographs on the Evaluation of Carcinogenic Risks to Humans. Vol. 34. Lyon: IARC.

Johnson A, CY Moira, L MacLean, E Atkins, A Dybunico, F Cheng, and D Enarson. 1985. Respiratory abnormalities amongst workers in iron and steel industry. Brit J Ind Med 42:94–100.

Kronenberg RS, JC Levin, RF Dodson, JGN Garcia, and DE Griffith. 1991. Asbestos-related disease in employees of a steel mill and a glass bottle manufacturing plant. Ann NY Acad Sci 643:397–403.

Landrigan, PJ, MG Cherniack, FA Lewis, LR Catlett, and RW Hornung. 1986. Silicosis in a grey iron foundry. The persistence of an ancient disease. Scand J Work Environ Health 12:32–39.

National Institute for Occupational Safety and Health (NIOSH). 1996. Criteria for a Recommended Standard: Occupational Exposures to Metalworking Fluids. Cincinatti, OH: NIOSH.

Palheta, D and A Taylor. 1995. Mercury in environmental and biological samples from a gold mining area in the Amazon Region of Brazil. Science of the Total Environment 168:63-69.

Thomas, PR and D Clarke. 1992 Vibration white finger and Dupuytren’s contracture: Are they related? Occup Med 42(3):155–158.