Features
Tech Talk: Let’s talk air brakes

In Canada, unlike the U.S., if your municipality has a fleet garage it must conform to all the rules and regulations in that province. If you work in a fire department with its own apparatus division, you have a huge leg up. Not only can you have vehicles repaired by trained fire apparatus technicians, but the return to service time is also that much quicker as you’re not waiting for a salter or snow blower to be repaired first. 

As for driving a city salter, plow or over the road vehicle with air brakes, both fire and town or municipal workers must have the correct credentials. These include an air brake (Z) endorsement as well as a driver’s license with the correct class required to operate the vehicle in question. In some departments, including mine in Vaughan, a must-have hiring criteria is a Z-endorsement and a Class D driver’s license. However, even with these certifications, when new firefighters are hired, they will not be driving until they meet second class status.

This requires three to four years on the trucks and on the floor assisting before they are brought back as a second class firefighter to participate in a two-week in-house driving and pump course. When instructing these courses, you may think we do not spend time on the finer details of the Z-certification. They successfully earned the credential before they applied so they should know this stuff, right? So we thought.

I have been doing this for over 30 years and it is the same every time — you have to emphasize the importance of air brake basics. Recently, I asked one firefighter who has been on the trucks for six years to advise on cut-in cut-out pressures. They responded that they had not done that since their air brake exam before they started.

I looked at the firefighter with incredulity. They have an air brake endorsement now and drive fire trucks when on duty, but they don’t know what cut-in cut-out pressure is despite being taught before they started and retrained during our driver’s course? Not good. My suggestion is a training drill for all of your certified drivers annually on what their responsibilities are as DZ drivers, AZ drivers, or any other form of licenced driver with a Z-certification.  

In today’s day and age, highway traffic enforcement officers as well as your local or provincial police departments, have no problem stopping and questioning anybody behind the wheel of large class trucks, especially ones with air brakes.

Did you know that in Ontario fire departments are exempt from schedule one MTO pre-trip inspections? We are even exempt from emissions inspections and only have to register a licence plate once.

What this means is in the event of an accident, the driver better know his or her place behind the wheel. Just as if a driver is required to complete a road test, there will be questions with correct answers, which need to be known.

Brakes convert energy produced by the vehicle’s engine to move the equipment. To stop the vehicle, this kinetic energy must be converted into another form. This is called friction. Brakes convert the energy of a moving vehicle into heat through friction between a static and moving part. Once the two meet each other, friction is created, causing heat which must be absorbed. This is done first by the brake material and then by means of ventilation, allowing air to pass through the brake parts.

In most cases fire trucks only know two speeds: full speed and full stop. The amount of heat created depends on a few things, including weight, size of vehicle and road speed. Have you ever watched a Formula One or NASCAR race? If you happen to see a vehicle braking during a night race you may notice the brake parts go red, sometimes white hot, then turn black again as quick as they went red. These vehicles are not heavy, but they do go fast so a significant amount of braking is required to slow them down to a safe speed to take a corner. This is friction in action.

Large vehicles such as fire trucks create a lot more heat than passenger cars, which in turn creates significantly more concern. The drivers of these rigs must know about brake heat and its effect. 

Almost all passenger vehicles for the most part have hydraulic brakes, whereas about 80 per cent of fire or commercial trucks have air brakes depending on their class. Air brakes are used on commercial vehicles because they can transmit high mechanical forces over long distances. This keeps the cost of parts down. Fluid used in hydraulic systems cannot be compressed so the system must remain constantly full. Air brakes systems require all air lines to be full of air first before they will operate. 

For fire trucks, as well as other large vehicles using air brakes, the distance to travel between each part is extensive. Minor delays happen between all of these connected components every time the brake is applied and released. The air brake manuals outline that delays may range from three-tenths of a second to six-tenths of a second depending on the type of vehicle involved and may range from a half of a second to a full second on brake release. These are regulated under the air brake safety standards.

These delays are managed by special values in the system to make sure the time needed to travel between parts is as short as it can be — virtually undetectable. 

Air-over-hydraulic brakes are also common.  Know what your truck is equipped with so you know how to perform a proper truck check and identify any concerns. Some commercial vehicles, such as a Class 6, can have hydraulics with an air-operated parking brake, which, depending on your province, would require an air brake endorsement. Check with your local MTO if unsure.  

The air brake system is then broken down into separate systems. If your department has Z-endorsed drivers, they need to know how the dash gauges work. Which air tanks are which between the wet tank, primary, secondary and auxiliary.  If unsure, you can clearly label each with colour ties and create a legend for easy identification. 

Keep it simple so if you are asked by a police or MTO officer the correct answer is given. Know your cut-in and cut-out pressures and what they mean, as well as your brake chambers and what a brake adjustment looks like. Know how to mark and measure. Firefighters learn these things when they write the air brake test, but I bet if you ask them what their brake chamber is marked and measured at they will come back with “it checks out okay.” Not a good answer.  

Have all of your Z-endorsed drivers complete yearly competency drills and training to review and apply the air brake manual for your province. Do some in-house testing and invite your local MTO officer to discuss what they look for. Being proactive decreases the likelihood of something going wrong. 

In Ontario we did a fire department mechanical week at the fire college where we invited fire pump trainers, ladder representatives, tire specialists, and police and roadside inspection officers. These folks delivered presentations to show us what we need to know. You can do the same with driver training in the department. Remind your engineers and drivers to review air brakes and what their requirements are. 

Remember my friends: Rubber side down. Enjoy a safe and healthy summer.

Chris Dennis is the chief mechanical officer for Vaughan Fire and Rescue Service in Ontario. He can be reached at Chris.Dennis@vaughan.ca.