 |
| An EVT measures the slack adjuster with the parking brake released and no pressure on the brake pedal. (Fire Apparatus Photos by Brian Brown) |
 |
| An EVT measures slack adjuster travel while another technician in the cab steps on the brakes. The distance traveled was 1 3/8 inches. |
 |
| The chart shows when automatic slack adjusters should be readjusted for different sizes of air brake chambers based on federal DOT regulations. |
While many fire departments have a program in place that requires daily inspections of their fire apparatus, unfortunately many do not. A thorough daily apparatus inspection program should ensure that the apparatus is response ready and safe to drive.
Some states require that the engineers/driver operators of fire apparatus have a commercial vehicle driver license, and consequently a pre-trip inspection is required. One mandatory item is brakes, whether it is a required pre-trip inspection or a daily inspection.
Safety Advisory
Many fire departments do not take the time to make sure that operators are properly trained to identify problems associated with brakes. All air brake systems have components that need to be inspected and tested, including valves, lines, tanks, air dryers, brake chambers and slack adjusters. The most often overlooked issue is slack adjuster travel, and it’s one that requires professional assistance if adjustments are needed.
Last fall the National Institute for Occupational Safety and Health (NIOSH) issued a safety advisory that “manual adjustment of automatic slack adjusters may contribute to unexpected brake failure on automotive fire apparatus.”
NIOSH said all fire departments should make sure that maintenance is only performed by qualified technicians who meet the requirements of the National Fire Protection Association (NFPA) 1071 Standard for Emergency Vehicle Technician Profession Qualifications.
When an automatic slack adjuster is found to be out of adjustment, the NIOSH bulletin warned that it signifies the existence of a larger braking system problem that needs to be corrected immediately.
NIOSH officials said they issued the advisory in response to an investigation of a firefighter fatality and noted that the International Association of Fire Chiefs (IAFC) had issued a 2006 report warning of the dangers of manually adjusting automatic slack adjusters.
The NIOSH advisory noted that an automatic slack adjuster is a mechanical component of the air brake system that adjusts brakes as necessary when the vehicle is in operation to compensate for wear in the brake shoes (drum brakes) or pads (disc brakes).
All air brake systems have brake chambers that are identified as Type 20, Type 24, all the way up to Type 36. This number indicates the square inches of effective air pressure area that a brake chamber has. For example, in a Type 20, 20 square inches of effective air pressure area should be in the brake chamber. The most common type of brake found on fire apparatus is the clamp type “S” cam brake. The brake chamber is a diaphragm-type actuator that converts the energy of air pressure into mechanical force.
Slack adjuster travel is the distance traveled by the push rod in the brake chamber to the slack adjuster to apply the brakes. For instance, the maximum travel for a Type 30 brake chamber is 2 inches, or a 90-degree angle or less while looking at the slack adjuster. The maximum travel for other brake chambers varies depending on the size.
Maximum Travel
All the driver needs to verify is the maximum travel of the slack adjuster when the brakes are applied. This can be done by chocking the vehicle, placing someone in the driver seat (do not start the vehicle), releasing the parking brake and having the driver fan (apply and release) the brake pedal until the air pressure gauges attain 90-95 psi. The recommended air pressure reading when measuring the stroke travel is 80-95 psi. Then apply air pressure by stepping on the brake pedal and holding it in place.
Once all of this is carried out and it is safe, the driver operator can roll under the vehicle on a creeper and visually look at each slack adjuster at every wheel position. A tape measure can also be used to verify the slack adjuster travel by the inches moved when the brakes are released. The slack adjuster travel can be measured at each wheel position by stepping on the brakes several times. After the under-truck inspection is performed, if any slack adjusters exceed the maximum travel allowed based on a federal Department of Transportation standard, then they need to be adjusted.
Always have a certified emergency vehicle technician (EVT), Automotive Service Excellence (ASE) mechanic or Title 49 CFR 396.25 brake inspector handle any adjustments or repairs to your vehicle.
Inspection Items
Brake inspection items that can take a fire apparatus out of service are identified in several National Fire Protection Association standards: NFPA 1911, 2007 edition, the Standard for the Inspection, Maintenance, Testing, and Retirement of In-Service Automotive Fire Apparatus; NFPA 1071, 2006 edition, the Standard for Emergency Vehicle Technician Professional Qualifications; and NFPA 1002, 2009 edition, the Standard on Apparatus Driver/Operator Professional Qualifications. When complex problems occur always consult the manufacturer’s troubleshooting guidelines to accurately identify and repair the problem.
A few common out-of-service problems are: linings missing; audible air leak at chamber; linings/pad too thin; loose air chamber; loose or broken spider or camshaft bracket. Consult your NFPA standards documents or contact the commercial division of your state motor vehicle agency.
Slack adjuster travel is not the only item that needs to checked and inspected. The following are some other items that should be inspected when the shift starts. If you are a member of a volunteer department, you can check these items after you return and before the next call. While performing brake inspections, remember that no two vehicles operate under identical conditions, and maintenance intervals may vary.
Parking Brake Check
(Daily Inspection)
To adequately check the parking brake, refer to the NFPA 1901 and 1911 standards and your most current International Fire Service Training Association (IFSTA) and locate a steep grade. You may not be able to find a 20-percent grade in your area. While the driver operator is seated in the vehicle and is applying the service brakes, apply the parking brake and set the wheel chocks an inch or two forward of the front or rear tires. Have the engineer/driver release the brake pedal and check to see if the parking brake holds the truck on the grade.
The parking brake can also be tested by the engineer/driver operator alone. Place the unit on a flat surface. Be sure the brake will hold the vehicle by shifting into a lower gear and gently pressing the throttle so that a pull is created against the parking brake.
Hydraulic Brake Check
(Daily Inspection)
For a daily hydraulic brake check, with the engine running, apply firm pressure to the service brakes with the brake pedal and hold for five seconds. The brake pedal should not move (depress) during the five seconds.
If the vehicle is equipped with a hydraulic brake reserve (backup) system, leave the key off, and depress the brake pedal and listen for the sound of the reserve system electric motor. Also check that the warning buzzer and/or light are off.
Check the service (foot) brake operation by moving the vehicle forward slowly (about 5 mph) and apply the brake firmly. Note any vehicle “pulling” to one side, unusual feel or delayed stopping action.
DOT Air Brake Check
(Daily Inspection)
Air brake safety devices vary; however this procedure is designed to check that any safety device operates correctly as air pressure drops from normal to a low-air condition. For safety purposes, in areas where an incline is present, you will need to use wheel chocks during the air brake check.
The proper procedures for daily inspections of the air brake system are as follows:
- Test air leakage rate. With a fully-charged air system (typically 120 psi), turn off the engine, chock the wheels, release (push in) the parking brake button (all vehicles) and trailer air supply button (for combination vehicles and tillers) and time the air pressure drop. After the initial pressure drop, the loss rate should be no more than 2 psi in one minute for single vehicles and no more than 3 psi in one minute for combination vehicles.
- Test air brake system for leaks. With the parking brake (all vehicles) released (pushed in), apply firm pressure to the service brake pedal. Watch the air supply gauge and listen for leaks. After the initial pressure drop, the loss rate for single vehicles should be no more than 3 psi in one minute and no more than 4 psi in one minute for combination vehicles and tillers. If the air loss rate exceeds these figures, have the air system repaired before operating.
- Test low pressure warning alarm and/or signal. Turn the key to the “on” position. Rapidly fan (apply and release) the brake pedal to reduce air tank pressure. The low-air-pressure warning signal must come on before the pressure drops to less than 60 psi in the air tank. If the warning alarm/signal doesn’t work, you could be losing air pressure without knowing it. This could cause the parking spring brakes to activate suddenly. Remember, if this should happen while driving the vehicle, only limited braking can be done before the parking spring brakes automatically come on.
- Check that the spring brakes come on automatically. Continue to rapidly fan (apply and release) the service brake pedal to further reduce air tank pressure. The trailer air supply button, if it is a combination vehicle or tiller, and parking brake button should pop out when the air pressure falls to the manufacturer’s specification, usually between 20 to 40 psi. This causes the parking spring brakes to come on.
- Check rate of air pressure buildup. Based on current Department of Transportation standards, when the engine is operating at 1,200 rpms, the air pressure should return to 120 psi within 90 seconds in dual air systems. If the vehicle has larger than minimum air tanks, the build-up time can be longer and still be safe. Check the manufacturer’s specifications. Most fire apparatus have rapid air build-up tanks so your build up time could be considerably less. Know your fire apparatus. If the air pressure does not build up fast enough, the apparatus air pressure may drop too low while driving, requiring an emergency stop.
- Test service brakes. Wait for normal air pressure and then release the parking brake and trailer air supply button for combination vehicles or tillers. Move the vehicle forward slowly at about 5 mph and apply the brakes firmly using the brake pedal. Note any vehicle “pulling” to one side, unusual feel or delayed stopping action. This test may show you problems that you otherwise would not know about until you needed to use the brakes on the road.
Remember, if your brakes are marginally in adjustment when the brakes are cold, they will certainly be out of adjustment when the brake drums build heat. As the drums heat up, they expand and move away from the brake lining, causing the brake chamber pushrod and slack adjuster to travel even farther. Always have an EVT or a certified mechanic or brake inspector handle any adjustments or repairs.
Obviously, there are many ways to perform brake check inspections, and it is critical to have a program in place. If you don’t, your department is crossing a dangerous line with the lives of the firefighters and the citizens they are sworn to protect in the balance.
A daily inspection of the brakes is a proactive approach to improve apparatus safety while significantly
reducing the legal liability for any department. A well-oiled apparatus inspection and maintenance program is not just fleet maintenance, but also risk management.
I want to credit my friend Ralph Craven for his assistance with this column. Ralph, who has worked in apparatus maintenance for almost 40 years, has investigated many emergency vehicle accidents and has been instrumental in recalls for safety-related defects. Among his accomplishments, he is co-founder, officer and investigator of the National Institute of Emergency Vehicle Safety. He is also co-founder of the California Fire Mechanics Academy and former president of the Northern California Fire Mechanics Association, as well as a former member (10 years) of the NFPA 1901 committee.
Editor’s Note: Brian Brown is bureau chief of fleet services for the South Metro (Colo.) Fire Rescue Authority. He has over 30 years’ experience in fleet services, with more than 20 years in fire apparatus fleet services, and is a former president of the Colorado Fire Mechanics Association. His certifications include Master Automobile Technician, Master Medium/Heavy-Duty Truck Technician, Emergency Vehicle Fire Apparatus Technician Management Level I and Level II, Emergency Vehicle Technician Management I, Fire Fighter II, Fire Instructor I and Hazardous Materials Responder Technician.
More Fire Apparatus Current Issue Articles
More Fire Apparatus Archives Issue Articles
