ENGINE RETARDER AND MANUAL BRAKE LIMITING VALVE HAZARDS: THE NTSB REPORT
Responding to eight accidents involving fire apparatus, the National Transportation Safety Board (NTSB) published a special report in March 1991 that contained a critique of the accidents and four recommendations for increasing firefighter safety. Two of these recommendations—those pertaining to engine retarders and manual brake limiting valves—are discussed in this article and were the focus of the September 1992 “Apparatus Safety Bulletin” I prepared for the International Association of Fire Chiefs Maintenance Section. The entire NTSB report should be read, however, since it explains in detail the reasons that led the NTSB to issue the four recommendations.
The bulletin is in response to the NTSB’s request that the 1AFC inform fire departments nationwide of the potential hazards of misusing engine retarders and encourage fire departments to establish operating procedures consistent with manufacturers’ warnings about the improper use of engine retarders (H-91-8).
The Board also urged the 1AFC to encourage fire departments to discontinue using manual brake limiting valves (H-91-9).
The NTSB report was not complimentary of the fire service. It revealed that fire departments were overlooking manufacturers’ recommendations and that warnings issued by the NTSB were not being heeded. Among the Board’s findings were that engine retarders still were being used on wet roads despite numerous warnings from the NTSB, beginning as early as 1985, that retarders not be used under wet-road conditions. In addition, the NTSB report cited the use of engine retarders on wet surfaces when the weight of the vehicle had been substantially reduced—as is the case when the apparatus booster tank is empty—and the continued use of front axle brake limiting valves even after commercial drivers had been warned to stop using them, beginning in 1985.
The report also identified practices and schedules relating to vehicle maintenance, safety inspections, and the use of seat belts.
ENGINE RETARDERS
As our apparatus got bigger and heavier over the years, we began to use a variety of products identified as auxiliary brake systems, which grew in popularity during the ’70s and ’80s. One of them, the engine retarder, has become a standard on most heavy fire apparatus.
As is true in the case of many new apparatus features, a learning curve is involved. Today, far too many drivers of emergency apparatus still do not fully understand that the manner in which engine brakes and engine retarders are operated affects the safety and stability of the apparatus.
Literature and manuals that explain how engine retarders should be operated have been available. The Jacobs Manufacturing Company and the National Highway Traffic Safety Administration (NHTSA), for example, each has published booklets on techniques for driving with engine retarders (Jacobs Manufacturing Company: “Professional Driver Techniques and Owners Manual,” Form No. 011390 100M HU-3-86; NHTSA: “A Professional Truck Driver’s Guide on the Use of Retarders,” DOT HS 806675, January 1985).
An engine retarder basically uses die engine itself to help slow down and control the emergency vehicle. When the retarder is activated, it alters the engine’s exhaust so that the engine is converted to a power-absorbing air compressor. This powerabsorbing function provides a retarding action completely through the transmission and drive lines to the drive axle of the apparatus. Keep in mind this braking effect is only on the drive axle; it does not involve the front axle or steering axle except in the case of four-wheel or all-wheel drive.
Learning to drive with engine retarders is difficult. 1 will discuss here the use of an engine retarder with an automatic transmission, although many apparatus in the fire service have manual transmissions. The principles presented here for the automatic transmission—such as for down shifting—are the same.
Today’s fire apparatus are equipped with multispeed automatic transmissions, to meet current National Fire Protection Association standards. When this transmission is coupled with an engine retarder, it establishes a braking system different from the service brakes with which we are familiar. With service brakes, you push on the brake pedal and force goes to all wheels to slow the apparatus. The more pressure applied, the greater the slowing capacity. When an engine retarder is used, on the other hand, the force is determined by an on/off switch and also normally by a selection switch, where the slowing or braking capacity is predetermined by several selection options that vary with the model and make of the engine as well as other factors.
The important consideration with regard to engine retarders is that braking is predetermined and consistent with the selections made before braking; in other words, the driver/ operator selects in advance the amount of retarding action that he/she wants.
The difficulty with doing this is that the system and its functions are controlled by the engine and its speed. In addition, the driver/operator activates the retarding system in a proactive manner before it is needed or used. During emergency responses, we face many varied situations that require numerous brake applications—herein lies the problem.
The engine retarders are on the input end of the transmission, which means the retarder provides a wide selection of braking options that vary with the gear of the apparatus when the retarder is activated. The gearing effect of the transmission is transmitted through the drive line and drive axle to the tires and road surfaces. The lower the gear selections, the higher the degree of braking or retardation. Also of prime importance here is that the driver is acting and reacting to surrounding traffic and conditions when responding to an emergency. Keep in mind also that the driver controls the service brakes according to prevailing conditions. The retarder activates as soon as the driver’s foot is removed from the throttle. The amount of braking that occurs is controlled by the preselected settings of the switches and controls, a constant; the gear the transmission is in at the time, a variable; and the engine speed, a variable.
As you can see, two of the three items mentioned are variables. The driver, therefore, constantly must be aware of them when using the engine retarder in conjunction with the apparatus service brakes. The bottom line is that the operator must learn to adjust the pressure used on the service brakes according to how the engine retarder will react under a specific set of conditions. Doing this is not difficult for an experienced driver under normal dry road conditions. The degree of difficulty increases substantially, however, when roads are damp or wet. The Jacobs Company manual mentioned above warns of the dangers of using the retarder when operating on wet, damp, or slippery road surfaces. The manual cautions that the driver should not use the retarder until he/she is sure that the truck is maintaining traction without its use and then should use the lower power settings on the retarder. The NHTSA’s manual directs drivers to turn off engine retarders when driving empty trucks on wet pavement.
In addition, research conducted in 1982 and 1983 by the Transportation Research Institute of the University of Michigan and sponsored by the NHTSA concluded the following:
- Drivers of retarder-equipped vehicles should be informed that they may avoid potential control problems by turning off the retarders when operating empty or lightly loaded apparatus on wet and slippery road surfaces.
- An experienced driver could not recover from a skid on a wet surface when turning an empty vehicle while decelerating with the engine retarder engaged.
A recent safety tip published by the Jacobs Manufacturing Company recommends that when weather conditions become wet and dangerous, the drivers/operators go to the lowest level of retardation and then moderate their speed and action. Almost everyone agrees that retarders should be used limitedly or be turned off when roads are wet and slippery. Keep in mind that when it rains the water begins to lift oil and grease from the road’s pores up to the surface. It can be almost as dangerous as driving on ice. The longer it has been since the last rain, the worse the problem will be, as the oil and grease accumulate over time, The first 10 or 15 minutes are the most dangerous. Every precaution should be taken to improve apparatus stability and control during this period of time especially. Turning the engine retarder off during these situations is the safe and prudent approach.
Special attention also is needed when decelerating on turns and when using downhill ramps to exit a highway. Often the service brake is used with the engine retarder during these operations. Too often the result is premature rear axle lockup and consequent loss of control.
Unfortunately, no fire service publications or manuals at the national level address these safety issues. One nationally published fire service manual, in fact, makes the following statement when discussing engine brakes and retarders: “Both devices save wear on the service brakes and make the apparatus easier to manage on hills and slippery roads.”
Even though the manual goes on to recommend that drivers become thoroughly familiar with all manufacturers’ recommendations—which is excellent advice—the warning is preceded by the above quote, which is not consistent with warnings and recommendations issued by the NTSB, the NHTSA, the Jacobs Manufacturing Company, and others with respect to slippery road surfaces.
To avoid the possibility of jeopardizing firefighter safety by improper/ unsafe use of engine retarders, your department should do the following:
- Read the NTSB special investigation report on emergency fire apparatus.
- Make sure that all drivers read and understand the manufacturers’ instructions for the types of engine retarders used in your department.
- Institute and enforce these safety recommendations in your emergency vehicle driver programs immediately.
- Update information in your driver training programs and fire service manuals to reflect the dangers of using engine retarders on wet and slippery road surfaces.
FRONT BRAKE LIMITING VALVES
Most fire apparatus manufactured before Federal Motor Vehicle Safety Standard #121 (FMVSS-121) was adopted in March 1975 were equipped with a front brake limiting valve. Typically, it was controlled by a dashboard switch or level marked with two positions, slippery road and dry road. The original purpose of this device was to help maintain apparatus control on wet or slippery roads by reducing the air pressure on the front brakes by 50 percent when the limiting valve was placed in the slippery road position. The intent was to eliminate front steering axle lockup, thereby allowing the driver to continue to steer the apparatus under heavy braking conditions even when the rear wheels were locked and skidding. An operator manual from a 1970 model truck even went so far as to state, “This assists you in holding a straight stop or when you are turning and braking at the same time on wet roadways.”
The problem is that none of these operator manuals addressed the fact that stopping distances were increased significantly when the limiting valve was in the slippery road setting. In addition, since these pieces of apparatus were built (prior to 1975), NHTSA research has shown (as early as 1985) that two-axle vehicles with weight comparable to fire apparatus consistently performed better with the front axle limiting valve in the dry road position, even on wet surfaces. It further stated: “Use of limiting valves on this type of vehicle appears unwise; it degrades performance.”
As a result of this research, the NTSB concluded that because fire apparatus often stop suddenly, because they frequently are operated at higher speeds than conventional vehicles, and because they are operated under hazardous conditions, using manual brake limiting valves can diminish the apparatus’ stopping capability and, therefore, use of the valves should be discontinued.
Again, the problem is to get word out to fire service drivers. Virtually no information is available through fire service-related instructional manuals to support the NTSB position. A recently published national fire service training manual released in 1989 addresses neither the issue of increases in stopping distances nor that of discontinuing using the limiting valves altogether.
To prevent accidents involving these valves, all drivers of emergency fire apparatus should do the following:
- Discontinue the use of the slippery road position on all apparatus equipped with front brake limiting valves.
- Post, placard, or otherwise lock out the front brake limiting valve so that it cannot be used accidentally.
- Update driver training programs and fire service manuals to include information that reinforces the NTSB position that front brake limiting valves not be used.
NATIONWIDE NETWORK NEEDED
The intent of the IAFC bulletin is not to criticize or place blame on the fire departments that have not followed proper procedures and recommendations. It is much more important that we learn from our mistakes and work to disseminate the lessons we have learned in the past. Because the fire service in this country is so diverse and different organizations serve different groups, it is very difficult to get the word out to fire departments that need the information. The U.S. Fire Administration of the Federal Emergency Management Agency is the recognized government entity at the federal level and is best equipped to reach the vast number of departments. My hope is that all national fire service organizations will work together with the USFA to get this information out to all fire departments across the country as quickly as possible.
Many have indicated that they would like to establish a nationwide network to share vital information— such as apparatus safety and maintenance issues. Unfortunately, lack of commitment or funds so far have kept that goal from becoming a reality.
To rectify the situation, the fire service, collectively, should ask the National Fire Academy to establish at least one current nationwide program that addresses fire apparatus specification, care, and maintenance issues. With the support of all of the nation’s fire service organizations, maybe such a network can become a reality.
