AIRBAG
PERFORMANCE
What you need to consider before
installing an Airbag:
Communication
At Destination
There’s No Air in The Bag
Same Bag 8 Hours Later
An Obvious Leaker?
PROCEDURE FOR INSPECTION /
ROOT CAUSE ANALYSIS
• Upon receipt, the DEF48096FF
airbags were visually inspected for
any obvious defects and none were
noted. The airbags were then leak
tested and no issues were noted.
After being disassembled, the
bladders were inflated for leak
testing and monitored for pressure
loss. At the conclusion of leak
testing, the bladders were found to
have maintained air pressure and
no defects were identified. It was
noted that the bladders revealed
several stress spots, which were not
obviously visible on the outer shell
5 Predictors of an Airbag’s Performance
1. Origin Application
• Bag Size
• Void Width
• Protection from abrasion and puncture
• Prevention of airbag dislodgement
2. Origin Gauged Pressure
3. Transit Altitude Changes
4. Transit Temperature Changes
5. Transit Void Width Changes
A Case Study:
75 miles from Roseville to Donner Pass
Union Pacific Switch Yard
Donner Summit (Cal Trans)
164 Feet Above Sea Level
7239 Feet Above Sea Level
Elevation and Atmospheric Pressure
• Gas expands as altitude increases, because
there is less pressure on it from the
surrounding atmosphere.
• At Sea Level the atmospheric pressure in PSI
is 14.7. As you increase in altitude the
atmospheric pressure drops at a predictable
rate, so you wouldn’t be too far off in saying
that pressure drops/gains about one half a
pound per square inch per 1000 feet in
elevation…and gains at the same rate as you
descend below sea level.
Atmosphere Overcomes Internal Pressure
14,000
9,000
1,000
Equalizing Pressure
Altitude Pressure Change
Starting Bag Gauged Inflation Pressure
Starting Altitude at Bag Inflation
Starting Atmospheric Pressure
Absolute Internal Bag Pressure
2.0 PSIG
164
14.61 PSIA
16.61 PSI
Ending Altitude
Ending Atmospheric Pressure
7239
Internal Pressure Change
Ending Bag Gauged Internal Pressure
3.37
11.24 PSI
PSI
5.4 PSIG
Temperature and Pressure
• Gay-Lussac’s Law (Amonton’s):
• When temperature increases, pressure increases.
•
•
•
•
When temperature decreases, pressure decreases in
direct relationship. (We will use absolute temperature, so
we’ll convert to Kelvin: 291k)
P₁ / T₁= P₂ / T₂
2.0 / 290.372k= P₂ / 282k
.00689 · 282.039k = P₂
1.943= P₂
As Elevation Goes Up, Temp Goes Down
(sometimes)
Temperature Pressure Change
Starting Atmospheric Temp at Inflation
Starting Bag Volume
Starting Bag Gauged Inflation Pressure
Ending Acclimated Temp at Deflation
Ending Bag Volume
Ending Bag Inflation Pressure
Internal Pressure Change
63 F
1 Constant
2.0 PSIG
48 F
1 Constant
1.9 PSIG
-0.05736 PSIG
Void Size or Volume and Pressure
• Boyles Law
• There is an inversely proportional relationship between
pressure and volume: the cubic area constraining the
gasses. Assuming a constant temperature.
• P₁·V₁=P₂·V₂
• 2.0·13,824=P₂·19,584
• 27,648/19,584=P₂
• 1.4=P₂
The Railroad Always Reveals Slack
Void Width
Starting PSI Measurement at Inflation
Starting Bag Volume: Length
Width
Void Width
Volume
Constant
2.0 PSIG
48 Inches
48 Inches
6.0 Inches
13824.0 CU IN
1
Void Width At Destination
Destination Volume
Destination PSIG
8.5 Inches
19584 CU IN
1.41
Internal Pressure Change
-0.59
PSIG
Still, Our Pressure More Than Doubled
Combination Pressure Change
2.7
PSIG
Considerations
• Insure Proper Initial PSI. Recheck after 30 minutes.
• Insure a compliant finished void width.
• Proper Application:
1. Pallet Unitization.
2. Bag Sized to the Lading.
3. Add Rigid Dunnage to Avoid Product Deformation.
• No Slack in the Load-Address all Under hangs.
• Familiarize Yourself With the Transit Topography and
Seasonal Weather conditions.