Metalworking fluids (MWFs) are used to reduce
heat and friction and to improve product quality in industrial machining
and grinding operations. There are numerous formulations, ranging
from straight oils (such as petroleum oils) to water-based fluids,
which include soluble oils and semisynthetic/synthetic fluids. MWFs
may be complex mixtures of oils, emulsifiers, anti-weld agents,
corrosion inhibitors, extreme pressure additives, buffers (alkaline
reserve), biocides, and other additives. In use, the fluid complexity
is compounded by contamination with substances from the manufacturing
process (such as tramp oils, hydraulic fluids, and particulate matter
from grinding and machining operations). Furthermore, water-based
metalworking fluids support microbial growth, which introduces biological
contaminants (such as bacterial and fungal cells or cell components
and their related biological byproducts such as endotoxins, exotoxins,
Some 1.2 million workers in machine finishing, machine tooling,
and other metalworking and metal-forming operations are potentially
exposed. Workers can be exposed to the fluids by breathing aerosols
generated in the machining process, or through skin contact when
they handle parts, tools, and equipment covered with the fluids.
The National Institute for Occupational Safety and Health (NIOSH)
defines MWF aerosol as the mist and all contaminants in the mist
generated during grinding and machining operations involving products
from metal and metal substitutes.
Occupational exposures to metalworking fluids may cause a variety
of health effects. Respiratory conditions include hypersensitivity
pneumonitis (HP), chronic bronchitis, impaired lung function, and
asthma. Work-related asthma (WRA) is one of today’s most prevalent
occupational disorders, imposing significant costs in healthcare
and workers’ compensation. Dermatologic exposures are most
commonly associated with, but not limited to, allergic and irritant
dermatitis (skin rash). In addition, substantial evidence shows
that past exposures to some metalworking fluids were associated
with increased risk of some types of cancer. Although actions taken
in the last several decades have reduced that risk, it is not known
if these actions have totally eliminated the risk.
NIOSH recommends that exposures to MWF aerosols be limited to 0.4
milligrams per cubic meter of air (thoracic particulate mass), as
a time-weighted average concentration up to 10 hours per day during
a 40-hour workweek [http://www.cdc.gov/niosh/98-102.html].
The recommended exposure limit (REL) is intended to prevent or greatly
reduce respiratory disorders associated with MWF exposure. Some workers
have developed WRA, HP, or other adverse respiratory effects when
exposed to MWFs at lower concentrations. This REL is technologically
feasible for most metalworking operations.
NMAM method 5524
NIOSH -specified technioque for estimating doses due to inhilation of MWFs.
Several preventive measures are available to reduce MWF exposures
and their effects. Formulations have been developed with safer, less
irritating additives and MWF components. Machinery has been modified
to limit the dispersal of MWF mists. In addition, the use of protective
gloves, aprons, and clothing, the education of workers regarding the
safe handling of MWFs, and the importance of workplace personal hygiene
are all key to controlling the exposures to MWFs.