The braking system
of a vehicle uses hydraulic power generated by a master cylinder to activate the
four-wheel brake assemblies. The
hydraulic power is transmitted throughout the brake system via brake fluid.
Brake fluid is a special liquid formulated from a silicone based or
glycol based product. Brake fluid
is not developed through the petroleum fractionating process.
There
are three classes of brake fluid commonly used in modern automobiles: DOT 3, DOT
4, and DOT 5. These are Department of Transportation specification grades; the
increasing numbers reflect increased boiling point. DOT 3 and DOT 4 are glycol
based, with DOT 3 most commonly used in disc brake systems. The glycol base is
hygroscopic (meaning it tends to attract water), and as such DOT 3 and 4 brake
fluids are most often changed when contaminated with moisture, which could boil
and cause erratic brake operation. DOT 5 is a silicone-based fluid that has a
higher boiling point and is much less hygroscopic than the glycol-based fluids.
Due to its relative expense, DOT 5 fluids are not normally seen in production
vehicles, but rather in racing applications that involve heavy braking.
More information on types of brake fluid can be found in Appendix J.
Brake fluid should not be dumped into septic systems, gutters, and storm
systems or onto the ground. It
should not be disposed of in the trash. Used
bake fluid is a hazardous waste and cannot be released into the environment.
The greatest safety issue with brake fluid is eye damage. Always use safety glasses when working around brake fluid. Gloves are also a good idea as dermal absorption does occur. Modern anti-lock brake systems have very high-pressure accumulators that could cause injury if not discharged properly. Consult service manuals for correct procedures.
Consult the MSDS for brake fluid to determine its makeup. If an automotive fluid contains toxic additives or contaminants it will have to be managed as a hazardous waste . All used brake fluid must be collected separately, labeled, and disposed of as a hazardous waste.
Brake fluid is hygroscopic, that is, it absorbs moisture. Do not keep a large stock of brake fluid on hand. Maintain an inventory only large enough to do the work at hand. If brake fluid is allowed to absorb moisture, it must not be used and is therefore wasted. Use the smallest container possible to avoid brake fluid “leftovers”.
Brake fluid can be included in some recycling programs but should not be
mixed with engine oil as part of an oil recycling or re-refining process.
The determination of the hazardous characteristic of used brake fluid depends on its initial composition (some brands contain hazardous constituents) and whether it has been contaminated during use or vehicle servicing. Brake fluid can become contaminated with chlorinated solvents if brake cleaner is carelessly sprayed into it during brake repairs. Most brake fluids are glycol based and should not be added to used oil. Brake fluid can pose serious health and safety risks if disposed of improperly. As a glycol based product it cannot be mixed with used oil for disposal. Brake fluid can be recycled.
In the event that the shop services vehicles that use silicone-based DOT
5 brake fluid, you may be required by your waste hauler to keep the glycol-and
silicone-based brake fluids separated. The two types of brake fluids are
color-coded to aid in identification: glycol-based DOT 3 and DOT 4 brake fluids
are clear to amber, while silicone-based DOT 5 brake fluid is purple.
DO
DO NOT