By Chris Daly

A common question I am often asked is: “How many feet does it take to stop if I am going X miles per hour?”

The answer to this question is, “It depends.” The actual question should be, “What is the total stopping distance of my vehicle at X miles per hour?” Total stopping distance is one of the most important concepts a fire apparatus operator must understand.

Perception and Reaction

Total stopping distance is that distance which takes into account all the steps necessary to bring a moving fire truck to a complete stop. Drivers must understand that this distance is more than just the distance necessary to slow the vehicle down and come to a stop. Total stopping distance also includes the time it takes an operator to see a hazard in the roadway, process this hazard in his brain, and send signals to his arms and legs to press the brake pedal or turn the wheel to avoid a hazard. This part of the process is known as perception and reaction distance.

When discussing perception and reaction distance, it is important for fire apparatus operators to understand speed in terms of feet per second (fps) instead of miles per hour (mph). A speed of 60 mph is equal to 88 fps. So in one second, your vehicle will traverse 88 feet. Stop and think about that. It takes the average person around 1.6 seconds to see, process, and react to a hazard. This means that at 60 mph, it takes you 140 feet just to realize there is a problem up ahead and start pushing your foot down on the brake pedal or turning the wheel. This is your perception and reaction distance.

Calculating perception and reaction distance is actually quite simple:

1. Convert the vehicle’s speed from mph to fps by multiplying the speed in mph by 1.466.
2. 60 mph × 1.466 = 87.96 (88).
3. Multiply the vehicle speed in fps by 1.6 seconds, which is the average reaction time for a sober, daylight driver.
4. 88 fps × 1.6 = 140.8 (140) feet.
5. The reaction distance at 60 mph is 140 feet.

Once an operator has perceived and reacted to the hazard, and his foot starts pressing down on the brake pedal, he is now initiating the braking process. Most drivers aren’t skilled enough or experienced enough to master the art of threshold braking (see “Introduction to Braking Energy,” Fire Apparatus & Emergency Equipment, August 2015). Instead, most drivers tend to lock up their wheels and start skidding. As we’ve discussed in previous articles, once the vehicle starts to skid, the driver has no steering control. The vehicle will skid in a straight line until it comes to a stop or strikes an object-i.e., crashes. If the vehicle is equipped with anti-lock brakes, the driver will be able to maintain steering control during the skid; however, the stopping distance will remain relatively the same. (See “Brake Fade and Antilock Brake Options,” October 2015.)

Stopping Distance

Having determined the perception and reaction distance, we must now determine the distance that the vehicle is going to skid-the stopping distance. Before discussing stopping distance, we must first discuss the roadway the operator is driving on. Every roadway has a certain stickiness or, in technical terms, coefficient of friction. This coefficient of friction is a value measured with specialized equipment that gives crash reconstructionists an idea of how sticky the road is. A dry, asphalt road that was recently paved can have a coefficient of friction as high as 0.9. A wet, worn-down road can have a coefficient of friction of 0.4 or less. The r

By Chris Daly

A common question I am often asked is: “How many feet does it take to stop if I am going X miles per hour?”

The answer to this question is, “It depends.” The actual question should be, “What is the total stopping distance of my vehicle at X miles per hour?” Total stopping distance is one of the most important concepts a fire apparatus operator must understand.

Perception and Reaction

Total stopping distance is that distance which takes into account all the steps necessary to bring a moving fire truck to a complete stop. Drivers must understand that this distance is more than just the distance necessary to slow the vehicle down and come to a stop. Total stopping distance also includes the time it takes an operator to see a hazard in the roadway, process this hazard in his brain, and send signals to his arms and legs to press the brake pedal or turn the wheel to avoid a hazard. This part of the process is known as perception and reaction distance.

When discussing perception and reaction distance, it is important for fire apparatus operators to understand speed in terms of feet per second (fps) instead of miles per hour (mph). A speed of 60 mph is equal to 88 fps. So in one second, your vehicle will traverse 88 feet. Stop and think about that. It takes the average person around 1.6 seconds to see, process, and react to a hazard. This means that at 60 mph, it takes you 140 feet just to realize there is a problem up ahead and start pushing your foot down on the brake pedal or turning the wheel. This is your perception and reaction distance.

Calculating perception and reaction distance is actually quite simple:

1. Convert the vehicle’s speed from mph to fps by multiplying the speed in mph by 1.466.
2. 60 mph × 1.466 = 87.96 (88).
3. Multiply the vehicle speed in fps by 1.6 seconds, which is the average reaction time for a sober, daylight driver.
4. 88 fps × 1.6 = 140.8 (140) feet.
5. The reaction distance at 60 mph is 140 feet.

Once an operator has perceived and reacted to the hazard, and his foot starts pressing down on the brake pedal, he is now initiating the braking process. Most drivers aren’t skilled enough or experienced enough to master the art of threshold braking (see “Introduction to Braking Energy,” Fire Apparatus & Emergency Equipment, August 2015). Instead, most drivers tend to lock up their wheels and start skidding. As we’ve discussed in previous articles, once the vehicle starts to skid, the driver has no steering control. The vehicle will skid in a straight line until it comes to a stop or strikes an object-i.e., crashes. If the vehicle is equipped with anti-lock brakes, the driver will be able to maintain steering control during the skid; however, the stopping distance will remain relatively the same. (See “Brake Fade and Antilock Brake Options,” October 2015.)

Stopping Distance

Having determined the perception and reaction distance, we must now determine the distance that the vehicle is going to skid-the stopping distance. Before discussing stopping distance, we must first discuss the roadway the operator is driving on. Every roadway has a certain stickiness or, in technical terms, coefficient of friction. This coefficient of friction is a value measured with specialized equipment that gives crash reconstructionists an idea of how sticky the road is. A dry, asphalt road that was recently paved can have a coefficient of friction as high as 0.9. A wet, worn-down road can have a coefficient of friction of 0.4 or less. The r

By Chris Daly

A common question I am often asked is: “How many feet does it take to stop if I am going X miles per hour?”

The answer to this question is, “It depends.” The actual question should be, “What is the total stopping distance of my vehicle at X miles per hour?” Total stopping distance is one of the most important concepts a fire apparatus operator must understand.

Perception and Reaction

Total stopping distance is that distance which takes into account all the steps necessary to bring a moving fire truck to a complete stop. Drivers must understand that this distance is more than just the distance necessary to slow the vehicle down and come to a stop. Total stopping distance also includes the time it takes an operator to see a hazard in the roadway, process this hazard in his brain, and send signals to his arms and legs to press the brake pedal or turn the wheel to avoid a hazard. This part of the process is known as perception and reaction distance.

When discussing perception and reaction distance, it is important for fire apparatus operators to understand speed in terms of feet per second (fps) instead of miles per hour (mph). A speed of 60 mph is equal to 88 fps. So in one second, your vehicle will traverse 88 feet. Stop and think about that. It takes the average person around 1.6 seconds to see, process, and react to a hazard. This means that at 60 mph, it takes you 140 feet just to realize there is a problem up ahead and start pushing your foot down on the brake pedal or turning the wheel. This is your perception and reaction distance.

Calculating perception and reaction distance is actually quite simple:

1. Convert the vehicle’s speed from mph to fps by multiplying the speed in mph by 1.466.
2. 60 mph × 1.466 = 87.96 (88).
3. Multiply the vehicle speed in fps by 1.6 seconds, which is the average reaction time for a sober, daylight driver.
4. 88 fps × 1.6 = 140.8 (140) feet.
5. The reaction distance at 60 mph is 140 feet.

Once an operator has perceived and reacted to the hazard, and his foot starts pressing down on the brake pedal, he is now initiating the braking process. Most drivers aren’t skilled enough or experienced enough to master the art of threshold braking (see “Introduction to Braking Energy,” Fire Apparatus & Emergency Equipment, August 2015). Instead, most drivers tend to lock up their wheels and start skidding. As we’ve discussed in previous articles, once the vehicle starts to skid, the driver has no steering control. The vehicle will skid in a straight line until it comes to a stop or strikes an object-i.e., crashes. If the vehicle is equipped with anti-lock brakes, the driver will be able to maintain steering control during the skid; however, the stopping distance will remain relatively the same. (See “Brake Fade and Antilock Brake Options,” October 2015.)

Stopping Distance

Having determined the perception and reaction distance, we must now determine the distance that the vehicle is going to skid-the stopping distance. Before discussing stopping distance, we must first discuss the roadway the operator is driving on. Every roadway has a certain stickiness or, in technical terms, coefficient of friction. This coefficient of friction is a value measured with specialized equipment that gives crash reconstructionists an idea of how sticky the road is. A dry, asphalt road that was recently paved can have a coefficient of friction as high as 0.9. A wet, worn-down road can have a coefficient of friction of 0.4 or less. The r

By Alan M. Petrillo

Manufacturers offer several systems to fire departments, districts, and emergency medical services squads in the way of station exhaust systems to remove toxic vehicle exhaust before it can become a problem in apparatus bays, station living quarters, and office spaces.

Exhaust systems for emergency services buildings fall into two categories of equipment: source capture systems that attach a hose directly to a vehicle’s exhaust pipe and hoseless exhaust removal and air filtration systems.

Hoseless Systems

Air Vacuum Corp. makes the AIRVAC 911 engine exhaust removal system, says John Koris, Air Vacuum’s regional sales manager. “It’s a fully automatic system that requires no personnel intervention,” he says, “and the system removes both gases and particulates from diesel exhaust.”

Koris says AIRVAC 911 is a ceiling-mounted filtration system that suspends two- by two- by two-foot units over exhaust points to create a direct path into and through the unit. “When a fire department gets a call, the doors open and trigger door switches that have a photo-beam backup, kicking on the system so it can pick up any backwash as the apparatus leaves,” Koris says. “When the apparatus returns, the system kicks on automatically and extracts any exhaust put into the building.”

1 The Tully (NY) Hose Company chose Air Vacuum Corp.’s AIRVAC 911 engine exhaust removal system for its fire station. (Photo courtesy of Air Vacuum Corp.)

Koris notes that Air Vacuum uses a smart timer to make the system fully automatic. “The smart timer, located on the apparatus room floor or in a utility or communications room, runs all of the units on a cycle, usually of 15 minutes, to remove all the exhaust in the apparatus bays,” he says. “It also has a manual override to turn the system on, like during cold months when you might keep doors closed but want to check chainsaws and other gas-powered equipment.”

The number of units installed in a system depends on the engineering standards for the space involved, Koris points out. “Typically, the standards for exhaust removal in a fire station call for four to six air changes in the cubic footage of the apparatus bay, so you might have one unit per bay or piece of apparatus or one unit every two or three bays.” Filter change in the units is typically based on the level of activity, Koris adds. “Carbon filters have a life cycle, and we recommend a maximum of 24 months of use for them,” he says. “The prefilter should be changed quarterly.”

2 Air Vacuum Corp. installed its AIRVAC 911 engine exhaust removal system in this station for the Westerly (RI) Fire Department. (Photo courtesy of Air Vacuum Corp.)

Daniel Orto, president of Air Technology Solutions, says his company makes the AirMATION vehicle diesel exhaust removal system. “It is a standalone, ceiling-suspended air filtration process,” Orto says, “powered by a 3,000-cubic-feet-per-minute (cfm) direct-drive blower that pulls, directs, and removes diesel exhaust fumes.” Ort