Air Bag Progress Report 5:

        The purpose of this report is to determine if air bags can be set off by shock. We can tell by filtering the FARS data for 2008 (1) according to the following criterea:  Vehicle occupants only, front air bag deployed, and then determining the number of cases for each impact point and each manner of collision. In the strange way that FARS records data, they specify an initial and a principal impact point, the theory being that the two might not be the same. As you can see from the data, most of the time they are, but not always. In addition, they specify a Manner of Collision. Basically, the impact points give the location of the impact and the manner of collision gives the direction of collision and/or the part of the colliding vehicle which struck the vehicle it collided with. In order to help the reader better understand the FARS coding we reproduce the relevant instructions from the 2008 FARS coding manual (2) for police officers who write the accident reports. The instructions are often long, complicated, confusing, sometimes contradictory, and many police officers do not bother reading the fine print or worry too much about the details. There is really no need for them to do so since no one checks what they write. The reports are fed directly into the FARS data base from the local police department computers.

        Before referring to the tables which give the results, you may want to study the instructions below in order to better understand the data.

Injury Severity (INJ_SEV):

Definition: ANSI D16.1; 2.3.1 and 2.3.2

Each case must have at least one Person Level form with Injury Severity coded "4."

Code 1 (Possible Injury). A possible injury is any injury reported or claimed which is not a fatal injury, incapacitating injury or non-incapacitating evident injury. This includes: momentary unconsciousness, claim of injuries not evident, limping, complaint of pain, nausea and hysteria.

Code 2 (Non-incapacitating Evident Injury). A non-incapacitating evident injury is any injury, other than a fatal injury or an incapacitating injury, which is evident to observers at the scene of the accident in which the injury occurred. This includes: lump on head, abrasions, bruises and minor lacerations. This does not include limping (the injury cannot be seen). (See code "1").

Code 3 (Incapacitating Injury). An incapacitating injury is any injury, other than a fatal injury, which prevents the injured person from walking, driving or normally continuing the activities the person was capable of performing before the injury occurred. This includes: severe lacerations, broken or distorted limbs, skull or chest injuries, abdominal injuries, unconsciousness at or when taken from the accident scene, and unable to leave the accident scene without assistance. This does not include momentary unconsciousness. (See code "1").

Code 4 (Fatal Injury), must only be used if the death occurred within thirty consecutive 24-hour time periods from the time of the accident. Every effort should be made to determine that the Death Date was within thirty consecutive 24-hour time

Manner of Collision (MAN_COLL)

Angles:
03 Front-to-Side, Same Direction
04 Front-to-Side, Opposite Direction
05 Front-to-Side, Right Angle (includes Broadside)
06 Front-to-Side/Angle – Direction Not Specified

07 Sideswipe – Same Direction
08 Sideswipe – Opposite Direction
09 Rear-to-Side
10 Rear-to-Rear*
11 Other (End-Swipes and Others)*
99 Unknown

AIR BAG AVAILABILITY/DEPLOYMENT (AIR_BAG)

Element Values:

Blanks 00 Not Applicable – Not a Motor Vehicle Occupant

DEPLOYED (For This Seat)

01 From the FRONT (steering wheel, dashboard) 02 From the SIDE (door, seat, canopy) 07 From OTHER Direction (knee, airbelt, etc. ) 08 From MULTIPLE Directions 09 From UNKNOWN Direction

NOT DEPLOYED (For This Seat)

20 Air bag Available – NO DEPLOYMENT 28 Air bag Available – SWITCHED OFF

UNKNOWN IF DEPLOYED

29 Air bag Available – UNKNOWN IF DEPLOYED

NOT AVAILABLE

30 NOT AVAILABLE (This Seat) 31 PREVIOUSLY DEPLOYED/NOT REPLACED 32 DISABLED/REMOVED

99 UNKNOWN if Air bag Available (For This Seat)

This element is used to record air bag availability and deployment for this person. Code this element according to this person’s Seating Position, regardless of the motor vehicle’s Body Type or the age of the motor vehicle.

Code 00 (Not Applicable – Not a Motor Vehicle Occupant) should be used for any person who is not an occupant of a motor vehicle.

Seating Position (SEAT_POS)

Element Values:

00 Not a Motor Vehicle Occupant

11 Front Seat – Left Side (Driver’s Side)

12 Front Seat – Middle

13 Front Seat – Right Side

18 Front Seat – Other

19 Front Seat – Unknown

21 Second Seat – Left Side

22 Second Seat – Middle

23 Second Seat – Right Side

28 Second Seat – Other

29 Second Seat – Unknown

31 Third Seat – Left Side

32 Third Seat – Middle

33 Third Seat – Right Side

38 Third Seat – Other

39 Third Seat – Unknown

41 Fourth Seat – Left Side

42 Fourth Seat – Middle

43 Fourth Seat – Right Side

48 Fourth Seat – Other

49 Fourth Seat – Unknown

50 Sleeper Section of Cab (Truck)

51 Other Passenger in enclosed passenger or cargo area (includes passengers in 5th row of 15-seat, 5-row vans)

52 Other Passenger in unenclosed passenger or cargo area

53 Other Passenger in passenger or cargo area, unknown whether or not enclosed

54 Trailing Unit

55 Riding on Vehicle Exterior

99 Unknown

*These values are unlikely occurrences and will raise an error flag.

IMPACT POINT-INITIAL/PRINCIPAL (IMPACT1 and IMPACT2)

00 Non-Collision

01-12 Clock Points

13 Top

14 Undercarriage

Special Conditions 18 – This Vehicle Set Something In Motion Causing Injury or Damage (Not a Clock Point)

99 Unknown

IMPACT POINT-INITIAL: Code the point that identifies the area on this vehicle that produced the first instance of injury or property damage involving this vehicle. The event that produced the initial impact for this vehicle may or may not be the First Harmful Event for the crash.

IMPACT POINT-PRINCIPAL: Code the point that identifies the area on this vehicle that produced the most severe instance of injury or property damage involving this vehicle. If this vehicle only has collision events, then the event that produced the principal impact for this vehicle will be the Most Harmful Event for this vehicle.

If principal and initial impact points are the same, code both elements the same.

Codes "01-12" refer to the point on a clock. Refer to the diagram on the following page for examples of how to superimpose the clock point on several vehicle types.

It is important to note that impact point refers mainly to the area of the vehicle that sustained the impact and does not depend upon the attitude of the vehicle (e.g., damage to a grille is still damage at 12 o-clock even if it was caused by sliding sideways past a utility pole).

However, code "13 – Top" may raise questions. The front and rear windows of some vehicles may also be viewed from the top. It may also be difficult to code impacts to the hood and rear deck of a vehicle.

CLOCKPOINT DIAGRAM

      In order to avoid ambiguity we consider only those cases in which the initial and principal impact points are the same. First, however, we present a table to show how often that is the case for each clock point:

The following table shows the number of front air bag deployments for each clock point and manner of collision:

Manner of Collision

  We notice immediately that while the largest number of cases are front end, it is not possible to determine from the data how many of these are head-on. The 2008 edition of Traffic Safety Facts  (3) gives the percent of all collisions (not just fatal collisions) which are head-on as 2.3%. From the 2001 data (the last to give fatal head-on collisions as a separate category)  it was 13.7% of all fatal collisions. The manual actually says that collisions are to be considered front end as long as any portion of the front end is struck, regardless of the angle.

  For the purposes of this report, however, our main area of interest is the number of cases which are not front end. We see immediately the large number of cases where the vehicle was struck at 3 o'clock (passenger side) and 9 o'clock (driver side). An argument could be made that for manner of collision = 5, the vehicle would still experience a deceleration component in the axial direction. Even for manner of collision =4 the same argument could be made, although the trigger would have to be very sensitive to set off the air bag as a result. But what is really telling here is the number of rear end collisions (impact point 6). Here, manner of collision other than 1 makes no sense so these are probably coding errors. But the 202 cases where manner of collision = 1 leave no doubt that in these cases the air bag was set off by shock and not by the accelerometer.

(1) FSAS 2008. NHTSA Publication, Washington, D.C. (FARS nowadays is actually published in two different formats. We are using the SAS format here.Thus FSAS stands for FARS in SAS format).