1998-02-23

Brake Fluid Vaporization as a Contributing Factor in Motor Vehicle Collisions 980371

In August of 1994 the Major Accident Investigation Team (M.A.I.T.) became aware of a collision involving a well maintained five year old minivan with 79,000 miles. The collision resulted in the death of a 1½ year old child. The cause of the collision was loss of brake pressure due to vaporization of the brake fluid. Over the years other investigators within the state have occasionally suspected brake fluid failure as a possible link to the cause of certain collisions. However, there was no accident record data on motor vehicle collisions resulting from brake fluid failure, and no standardized procedure for inspecting a vehicle and identifying the cause of the collision as a brake fluid failure. The Washington State Uniform Collision Report has a classification for “defective brakes”. The category is not specific as to the type of defect in the braking system.
Currently, domestic manufacturers of motor vehicles do not list the regular changing of brake fluid as a scheduled maintenance item. (European/Asian manufacturers have a maintenance scheduling recommendation.) Police agencies do not typically have the equipment or an investigative procedure to identify fluid failure as a possible collision causing circumstance.
M.A.I.T., with the assistance of the Washington State Traffic Safety Commission (TSC) and the Washington State Department of Transportation (WSDOT), entered into a two phase testing program. The purpose was two-fold:
  1. 1
    To identify the typical brake fluid condition on the average motor vehicle and;
  2. 2
    To identify the conditions in which a collision investigator can recognize fluid failure as a collision causing circumstance.
The project was broken into two phases. Phase one consisted of developing a database of boiling points in randomly selected vehicles and documenting the boiling point of the brake fluid in relation to the make, model, year, mileage, and service type. This data was compared to available data from a New Zealand/Australia study completed several years ago.
Phase two involved the testing of three different classes of vehicles. The vehicles selected represented truck class, utility class and small passenger car class. The influence of vehicle classification and braking systems was compared with the manner and type of failure associated with vaporization of the fluid. A mixture of 5%, 3% and zero percent moisture contaminated fluid was used in the study.
The Washington State Patrol, Traffic Safety Commission and Department of Transportation entered into a contract with the University of Washington for the purpose of equipping the three test vehicles for phase two. The University was responsible for assisting in the selection of data acquisition equipment, calibrating thermocouples and sensors to work with the equipment, determining proper installation procedures according to established testing specifications and SAE standards, and overseeing the accuracy of the testing.

SAE MOBILUS

Subscribers can view annotate, and download all of SAE's content. Learn More »

Access SAE MOBILUS »

Members save up to 43% off list price.
Login to see discount.
Special Offer: With TechSelect, you decide what SAE Technical Papers you need, when you need them, and how much you want to pay.
X