1. Emergency Vehicle Operations Unit VI Theory and Principals of Vehicle Dynamics
This unit is the least exciting but probably the most important unit in the whole class. Students need to understand the forces present and how they effect our vehicles in order to understand why we continue to have incidents and need policies and enforcement.

2. Unit VI Objectives
The EVO will be able to identify reason why we crash
The EVO will be able to describe the physical forces that influence vehicle handling
The EVO will be able to identify the dynamics and physics behind large vehicle behavior and their relationship to vehicle speed and size

3. The manner in which the EV is driven to and from the emergency scene is the most important contributing factor that affects crash avoidance.
Excessive speed puts the EV driver in the
position of:
Being unable to negotiate curves
Being unable to stop before hitting another vehicle
Being unable to stop before entering an intersection
Loosing control due to weight shift
Losing control due to right side wheels leaving road surface
Losing control from poor road conditions such as pot holes, speed bumps, wet, icy or snowy road surfaces
Open discussion and get examples of each

4. Why Do We Crash Emergency Vehicles Responding and Returning from Calls?
Drive too fast
Don’t Stop at Intersections
Don’t wear our seatbelts
Refuse to use spotters
Fail to understand the difference between these vehicles and personal automobiles
Discuss each topic

5. Vehicle Dynamics Physical Forces Following Distances Braking Distances
Let’s look at:
Physical Forces
Following Distances
Braking Distances

6. Physical Forces Include:
Friction
Momentum
Inertia
Centrifugal Force
IF THEY ARE EXCEEDED, CONTROL IS LOST!

7. Physical Forces Always present Understandable Negative effects
Physical forces are understandable yet rarely understood

8. Physical Force Function Of: Size (mass) Speed (velocity)
Highway Geometry
Which do you control??
We totally control our speed
We have some control over size and weight of vehicle
Unless you work for the highway department you can not control how the road was built. You might be able to work with planning departments to make sure future roads are built with emergency vehicles in mind

9. Physical Forces Inertia- Newton’s 1st Momentum- Newton’s 2nd
Reaction-Newton’s 3rd
Friction- resistance to motion
Center of gravity
Velocity

10. Force Engine = 42,000 lbs. Ladder Truck= 56,000 lbs.
At 25 MPH = 47,250 lbs..
At 55 MPH = 115,500 lbs..
Ladder Truck= 56,000 lbs.
At 25 MPH = 63,000 lbs..
At 55 MPH = 154,000 lbs..
Look at the huge increase in force with an increase in either size or mass

11. KNOW THE CONDITIONS AND THE LIMITS AT WHICH TO STAY!
EXAMPLES:
Driving too fast for weather, road, or tire conditions
Accelerating too hard
Braking inappropriately
Changing directions too abruptly
KNOW THE CONDITIONS AND THE LIMITS AT WHICH TO STAY!
Anyone ever accelerated too fast and felt the wheel get loose?
Many accidents happen when the driver over corrects from a small problem.

12. Changing directions too abruptly caused this rollover.
Most accidents show that the vehicle does not go off the road and roll. Most times there is a series of over corrections and the rig will “pinball” back and forth several times before control is lost.

13. Why is friction important for vehicle control?
What is Friction?
Friction is the resistance to slipping.
Friction occurs whenever two surfaces rub together.
How many tires are on the ground?
What factors effect friction? Tire wear, proper inflation, ice, leaves
Why is friction important for vehicle control?

14. It would be impossible to control a vehicle without friction
It would be impossible to control a vehicle without friction. Friction enables the EV to stop, accelerate, and change direction.
Friction is a good thing. Just like fire is a good thing. When we control it!

15. Friction at the Brakes
The brake shoes pressing on the drums or pads clamping the disc create friction and slow the wheels.
The friction at the brake surfaces generates heat.
Heat due to excessive, hard braking creates brake fade. ( scary at best - deadly at it’s worst.)
Do we know how to ride brakes on a hill?

16. Coefficient of Friction
Measures how slippery a road is
Dry asphalt has a value of 0.8 to 0.9
Wet or icy roads drop to 0.2 or 0.3
The lower the value, the longer it takes to come to a complete stop
Can’t drive the same on warm dry days as you can on cold rainy days
Coefficient of friction effects our stopping distance

17. The Total Braking Distance =
Perception Distance
Reaction Distance
Brake Lag Distance
Braking Distance
What does total braking distance mean? Ask students
We think about actual stopping (skid mark) distance, BUT
It all adds up!

18. Perception Distance - How far the vehicle travels when the need to brake occurs and the driver recognizes that need.
Several Things happen before you hit the brakes

19. Reaction Distance – How far the vehicle travels as the driver reacts and applies the brake. (Perception/Reaction Distance based on 1.60 Second Reaction Time)
Most of this happens automatically, but it all adds time
Did I just see a deer? Now what do I do?

20. Brake Lag Distance – How far the vehicle travels from the time the brakes are applied and the vehicle begins to slow down. (Apparatus Equipped with Air Brakes – Air Lag Distance Based on 0.5 Seconds)
There is a series of mechanical stuff that happens in the vehicle itself.

21. Braking Distance – How far the vehicle travels from the brakes starting to slow the vehicle and the vehicle coming to a complete stop.
This is what we normal think of when we say braking distance.

22. Total Distance The total distance includes Perception Distance
Reaction Distance
Brake Lag Distance
Braking Distance
Each of these items however small they may seem add to make the total stopping distance.
When you factor in how many feet per second the vehicle is moving it becomes a large distance.

23. Vehicle weight and speed affect stopping distance.
The speed being equal, it will take a large tanker longer to stop than most pumpers.
Factor of momentum. The weight of the water in the tanker makes it a heavier vehicle then the pumper.

24. 2003 Seagrave Pumper w/Anti-Lock Air Brakes
GVW 36,900 lbs.
Reaction Time: 1.6 Seconds Air Lag Time: 0.5 Seconds
Speed / MPH
Reaction
Distance
Air Lag
Braking Distance
Total 10
23.47
7.34
6.54
37.34 20
46.94
14.67
26.14
87.76 35
82.15
25.67
80.07
187.89 45
105.62
33.01
132.35
270.98 55
129.10
40.34
197.71
367.15
Look at how the braking distance grows as the speed increases
This information obtained from:
Stephen A. Coulon Fire Service Instructor,
Collision Reconstruction Specialist,
Adjunct Instructor N.Y. City Fire Department
181 Quinnipiac Ave
North Haven, CT 06473

25. How Far is 367 Feet?
From blacktop to stands is 367’. Field is 100 yards (300’), each end zone is ten yards (2 equals 60’) and then extra grass strip(7’)
Notice how many tractor trailers would fit in that length.
How long does it take a kickoff returning to go end zone to end zone?
WOW that is a long ways!

26. Emergency Vehicle Operations
Stopping Distance
Perception Distance
Reaction Distance
Braking Distance
Speed, Weight, Road Surface
60 MPH = 88ft/sec
30 MPH = 44 ft/sec
Variables
By looking at speed in feet per second you can see how all the components of braking distance add up.

27. What Happens to this Distance if the Coefficient of Friction drops from 0.8 to 0.2 because of ice?
Can you even see something that far ahead to start the braking process?

28. Antilock Brakes
Anti lock brakes don’t make the vehicle stop any faster
This video is tractor trailers but all the same principles apply to big trucks and many of us now pull trailers for Haz-Mat, four wheelers, trench rescue etc.

29. Let’s first cover some basic terminology.
AIR BRAKES
Air brakes have many common applications in vehicles today.
They can be found on school busses, dump trucks, fire trucks and most any vehicle over pounds.
Let’s first cover some basic terminology.
The airbrake section is pretty self explanatory. If the department you are at uses airbrakes it is a good thing to cover. If not you may delete it.

30. Air compressor and governor
AIR BRAKES
Air compressor and governor
The air compressor pumps air into the storage tanks (reservoirs) this compressor can be driven by gears or most common a V-belt
The governor controls the pressure going to the storage tanks. When the air pressure reaches 130 psi depending on the system requirements the governor will shut the compressor off until a pressure loss is detected.

31. AIR BRAKES Air storage tanks
Storage tanks will hold enough air to allow the brakes to be used in the event the compressor stops working

32. AIR BRAKES Safety valve
A safety relief valve is installed in the first air tank (quick build up tank) this protects the braking system from over pressuring. This safety valve in most vehicles will pop off at 150 psi, then reset itself.

33. AIR BRAKES
Drain valve
The tank drain valve, when opened, will allow any moisture or water to be drained from the air tank at its lowest point. This valve should be opened at least once a week for 2 to 3 seconds then closed.

34. AIR BRAKES Brake drums, shoes, and linings.
Brake drums are located at the end of each axle and the wheels are bolted to the drums.
The brake shoes and linings are located inside the drums and push against the inside of the drum to provide friction needed for stopping.

35. AIR BRAKES
Air chamber
Holds the parking brake spring and applies pressure to a piston that will push on the s-cam. This will put pressure on the slack adjuster then to the brake pads.
Rear air chambers
Front air chamber

36. AIR BRAKES Air supply gauge
All air-braked vehicles have an air supply pressure gauge. This gauge allows the driver to see the pressure in the system at all times. This is also used to check for air leaks when the system is off.

37. AIR BRAKES Low pressure warning buzzer.
This warning device will give the driver an audible warning in the event the system air pressure falls to the danger zone. In most fire trucks this alarm will sound at 60 < psi. Should this buzzer sound when the vehicle is in motion locate a safe location to pull the vehicle to a stop and check the system for damage.

38. AIR BRAKE INSPECTION NFPA 1915-10-3 3.12 THROUGH 3.12.10.10
The breaking system shall be inspected and maintained in accordance with the manufacture’s service recommendations .
If no service recommendation exist the shortest interval recommendation by the braking system manufacture, based on time or mileage, shall be adhered to.

39. AIR BRAKE INSPECTION
The braking system should be inspected at least once a week. Many full time fire departments require there emergency vehicles to be checked at the start of each shift.
In the volunteer sector emergency response vehicles should be inspected at least once a week. The most important point to remember is to document each inspection and keep the records for not less than 5 years.

40. AIR BRAKE INSPECTION Wet dry switch (valve)
This switch (valve) will reduce the braking capacity of the front wheels to about 50% of normal. This will help to control the vehicle on wet or icy roads.
This switch should be in normal mode on dry roads.

41. AIR BRAKE INSPECTION
The entire braking system should be inspected by an ASE certified mechanic once a year or every 3000 miles.
There are some simple test that should be completed during all in-house inspections.

42. AIR BRAKE INSPECTION AIR LEAK-DOWN RATE NFPA 1915-10-3.12.10.9
With a fully-charged air system (typically 125 psi) turn the engine off and the wheels chocked and the barking brake off. Note the pressure and the time.
For single system, unit there should not be more than a 3 psi drop in one minute. If the pressure drop is more than 3 psi the system should be inspected for damage or leaks.

43. AIR BRAKE INSPECTION PARKING BRAKE TEST PROCEDURE.
With the system air pressure in the normal operating range and the driver in the vehicle with seatbelt on and the shifter in natural; the parking brake off, allow the vehicle to roll forward. Apply the parking brake and the vehicle should come to a rapid stop and prevent vehicle movement.

44. AIR BRAKE INSPECTION Compressor system
The compressor system should also be inspected for safe operation. Areas to be inspected will be the drive belt, hose fittings, and mounting brackets.
It should also be noted in the vehicle inspection form the pressure that the low air warning alarm starts and stops.

45. Air brakes and steep grades (Hills)
BRAKING TECHNIQUES
Air brakes and steep grades (Hills)
If you were faced with a 6% grade that went for a total distance of 6 miles and if you did not use any braking action during your decent.
With a vehicle with a GVW (gorse vehicle weight) of 38,000 pounds your speed would climb to 238 mph this is called terminal velocity. Therefore we must learn how to brake on hills.

46. AIR BRAKE OPERATION Down hill braking
For many years drivers of fire vehicles were taught to apply light steady brake pressure to keep vehicle speed in check during down hill braking.
This method is still taught to this day however after much testing and research this theory has been proven WRONG.

47. AIR BRAKE OPERATION Down hill braking con’t
SNUB braking is now the recommended method for downhill braking.
This method works by allowing the vehicle to speed up to the desired or posted safe speed then applying the brakes and slowing the vehicle down 5 to 10 mph below the posted speed.
Then allowing the speed to pick up and the process is repeated.

48. AIR BRAKE OPERATION Down hill braking con’t
By applying the brakes in this method there is time to allow the brakes and the brake drums to cool to help control heat buildup as well as to reduce the chance of brake fade .

49. Applying the parking brake.
AIR BRAKE OPERATION
Applying the parking brake.
Whenever you bring the vehicle to a total stop with the transmission in neutral, you must set the brake. If you are on an incline, turn the steer wheels towards the curb on a decline.
On an incline the wheels should be turned away from the curb.

50. 1. Inspect vehicle brake systems not less than once a week.
Key points to remember
1. Inspect vehicle brake systems not less than once a week.
2. Document each inspection and keep records for 5 years.
3. Have brake systems inspected by an ASE certified mechanic every 3000 miles or once a year.
4. Insure a good driver training program is in place and train all new drivers on air brake systems.

51. Following distance is influenced by:
Following Distances
Following distance is influenced by:
Reaction Distance =1.6 seconds and is the distance the EV travels from the time the operator recognizes the need to brake until the brake pedal is applied. (ADD .5 seconds for air lag)
Braking Distance =7.02 for a Pumper. The distance traveled from brakes being applied until the EV comes to a full stop is feet.
Other factors are the WEIGHT and MECHANICAL CONDITION of the EV.

52. Four SECOND RULE
Four Second Rule - Keep a separation of at least two seconds between the EV and the vehicle being followed
Four seconds is a good rule of thumb

53. When to increase following distance:
2 Seconds might be adequate for smaller trucks and speeds under 40mph
3 seconds should be used if traveling over 40mph
4 seconds should be used for emergency vehicles.
Greater distance is required under poor road conditions, overloaded vehicles, etc.
Another important factor here is understanding what the driver in front of you will do if you are in emergency mode.

54. Following Distance in The Emergency Mode
Many operator’s reactions and performance get worse under stress.
Motorist may react in unusual ways to lights and sirens. If they stop abruptly, the EV Operator will need as much distance as possible to respond.
A greater following distance permits the EV Operator to get “The Big Picture” of the traffic situation.
How often does the average driver encounter emergency vehicles on the road. Most areas this will be very rare and drivers do not know how to react.

55. Centrifugal Force
Centrifugal force is the force that tends to push a vehicle away from the center of the turning radius. .
Use a model truck or an eraser to show this point
So what happens when we have speed and a tight curve?

56. Centrifugal Force
The force that tends to make a body move away from the center of rotation
Pushes a vehicle out of a curve
4500lb Engine, 500’ 25 MPH = 3844 lbf
Same 55 MPH = lbf
Again, speed and weight play a major role
F=mv2/r

57. Obey posted speed limits in curves and exit ramps from highways.
Does anyone really look at speed signs on curves?
They should, they are there for more then to just give the DOT something to do.
Hey, what about the skid marks?
Do you think there is a reason they are there?
How does Center of Gravity play in here?
Skid marks should be a clue, others have made this mistake. DON’T REPEAT IT!

58. Critical Speed of a Curve
The speed at which the vehicle will loose control rounding a curve
The experience of the driver does not matter
Need to know the radius of the curve and the coefficient of friction to figure
If this speed is broken the vehicle will not stay on the road!
There is a speed at which no driver can control the vehicle

59. Ensure Safety at the Training
Things can go wrong even in training
Use this clip to show how the car drifts into a curve because of centrifugal force.

60. CENTRIFUGAL FORCE CLICK HERE Animated Video
In many areas we will face several different curves and angles of curves while responding

61. MOMENTUM is the product of a vehicle’s mass (weight) times its velocity (speed).
CENTRIFUGAL FORCE is the force that tends to push a vehicle away from the center of the turning radius.
This truck will continue down the road. Show it only as long as it takes to introduce the topic

62. CENTRIFUGAL FORCE: Is the force that tends to push a vehicle away from the center of the turning radius. The higher the speed, the greater the centrifugal force. The tighter the curve, the greater the effects of centrifugal force.
This clip shows the EV leaving the highway when the curve is entered at too high a rate of speed.

63. This type of signage indicates: Posted speed limit
Speed limit for vehicles over 8 ft high.
Speed limit for vehicles over 1 ton.
B. Suggested speed limit
Ask students what this type of sign indicates?

64. Emergency Vehicle Operations
Types of Control
Vehicle Control/Loss of Control
Velocity
Change in position in relation to Time
Acceleration, Deceleration, Braking
Directional
Steering

65. Emergency Vehicle Operations
Impact Force
Engine = 42,000 lbs.
At 25 MPH = 439 tons
At 55 MPH = 2125 tons
Ladder Truck= 75,000 lbs.
At 25 MPH = 784 tons
At 55 MPH = 3794 tons
Good example of how both velocity and mass effect force

66. Big Bang Theory The bigger it is and the faster it goes:
The BIGGER THE BANG WILL BE
This was a demo to test security barriers.
What do we have in our districts that would act the same?
Bridge supports
Bunker Silos
Jersey Barriers

67. Center of Gravity Center of Gravity
Center of gravity will effect how the vehicle handles in two ways.
First is side to side

68. Center of Gravity Center of Gravity Second is front to rear.
BOTH will have serious effects on how the vehicle handles

69. Community Expectations
How does Community Expectations affect our vehicles?
Where does all that extra equipment go?
How does it change the center of gravity?

70. Center of Gravity Which has a higher center of gravity?
Easy one here, but lets look at some others

71. Center of Gravity
Without these two vehicles side by side you might not even notice the extra height when you hop in to drive. The wheel base is also different and will effect how these two vehicles react compared to one another.

72. Center of Gravity What is in the upper compartments?
Does the load change when water tank is empty?
Notice how the truck is squatting, How does this effect friction and braking on front tires?

73. Center of Gravity Weight on top effects the center of Gravity
Notice the truck is already leaning
Replace that hose with speedy dry and what happens? More weight will be placed on that side of truck making the situation worse.

74. When Center of Gravity is exceeded
Even large trucks with long wheels bases will roll.

75. DRIVING SKILL AND EXPERIENCE
NFPA Standard 1500, Standard for Fire Department Occupational Health and Safety Program (2002) states: “The fire department shall provide training and education for all fire department members commensurate with the duties and functions that they are expected to perform. Members shall be provided with training and education appropriate for their duties and responsibilities before being permitted to engage in emergency operations.”
Again NFPA standards dictate training

76. Know What you are Driving
It is important to train EV drivers on the vehicle they will be expected to operate under emergency conditions.
Driving in Emergency mode and driving in normal traffic are two completely different animals.

77. Review Exercise is located on Page 68 of the student Training Manual.
Unit VI Review
The EVO will be able to identify reason why we crash
The EVO will be able to describe the physical forces that influence vehicle handling
The EVO will be able to identify the dynamics and physics behind large vehicle behavior and their relationship to vehicle speed and size
Review Exercise is located on Page 68 of the student Training Manual.