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Airbags: Is There a Price Limit on Safety?
««« By Susan Miller
Susan was a preservice teacher at the University of Western Ontario when she wrote this article. Susan was a recipient of the
2007 STAO Preservice Award for this submission.
Curriculum Connetion: SCH3U, Quantities in
Chemical Reactions & SCH4C, Chemical
Calculations units.
The following activities and worksheets were developed for
the SCH3U, Quantities in Chemical Reactions & SCH4C,
Chemical Calculations units. The aim is to allow the student
to become aware of the uses of stoichiometry in everyday
situations and to further their critical thinking process by
discussing an issue with which they are familiar.
Airbag technology was 30 years in development before it
was considered safe and reliable enough to employ in cars.
However, with increased safety, there is an increased cost
of insurance associated with vehicles due to the high costs
of repairs. In addition, there are still safety concerns for
underweight and under-height passengers and environmental concerns with disposal of airbags after deployment.
take for their own safety through the use of other safety
features such as seat belts.
In short, is the safety benefit of having airbags fitted in
cars outweighed by the high cost of insurance, deaths on
inflation and environmental concerns with disposal even
for a low-speed collision?
The lesson begins with an introduction to airbags, using
the newspaper style article included in this lesson plan.
Questions are provided at the end of the article to help
focus student discussion. The students will be given one of
six hats, (creativity, bad points, good points, organization,
emotions and information) and be required in their group
to come up with supporting stances for their hat. Then, in
a group that has one representative with each type of hat
(6 in the group in total), students will discuss their position. Time may also be taken to conduct Internet searches
to support their positions. The teacher may want to
It is well-known that airbags save lives and prevent serious injuries when cars are involved in high-speed accidents. In this activity, however, students are encouraged
to consider the implications of cost versus safety in a lowspeed collision. Students are asked to evaluate whether
the higher costs of repairs and disposal concerns associated with airbags are validated by increased safety.
Furthermore students are asked to consider whether
there is a level of personal responsibility that one should
Airbags: Is there a price limit on safety?
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include information about the cost of repairs for a vehicle
involved in a low-speed collision and the discussion about
the costs of insurance rates, if known.
Students are asked to consider following stakeholders in
their discussion and evaluation of this issue:
• Car drivers and passengers – safety versus expensive
insurance costs
• Insurance companies – expensive repairs, use of used
airbags instead of new
• Environment – recycling/disposing of used airbags.
The final activity is to write a letter to the editor of a news-
paper, voicing their opinion on the airbag article. In this
case, the student may take the stand they wish. This activity fits nicely with the ministry expectations for this unit as
students are able to see the application of chemical quantities and calculations in an example with which they will
be familiar. The letter to the editor provides a valuable
chance for students to demonstrate science literacy. In
addition, the stoichiometry pages that follow this discussion provide concrete examples of the importance of
chemical quantities and valuable practise exercises on a
real case.
Airbag Chemistry
In the 1980s, Lee Iacocca warned of problems surrounding the development of
airbag technology. He was concerned that
people would consider wearing seat belts
unnecessary and about the general safety
of the technology itself.
higher if the airbags are deployed. Upon
detonation, the fabric on the dash is torn
and therefore must be replaced. On modern cars, the labour involved in re-setting
the dashboard electronics is intensive and
therefore the cost is significant. New
airbags typically cost around $800-$1000.
Although many advances have been made
to allow more flexibility in the use of
airbags, these systems were developed for
the 1.72m, 82kg male sitting 25cm from
the steering wheel. Women and children
under 1.5m tall and weighing less than
50kg have been injured.
ed to produce nitrogen gas and sodium.
The nitrogen gas is used to fill the airbag
and protect the passenger. Sodium is,
however, a very reactive metal (it may be
sodium hydroxide if there is moisture in
the airbag) and therefore must be reacted
to allow for safe disposal.
Airbag technology was patented in 1953.
The reaction involved is an explosion,
similar to that used to launch the space
shuttle. It took 30 years to develop and
refine the technology to allow for safe
inflation in 40 milliseconds.
When a car is involved in a collision, the
sensors must be able to distinguish
between a minor bump and a crash. A
magnet holds a ball in place. If a car
decelerates quickly, a ball is released from
the magnets. This connects an electrical
circuit and this connection causes the
airbag to be deployed.
The following chemical reactions occur in
sequence upon detonation of an airbag:
1. 2NaN3 → 3N2 + 2Na
2. 10Na + 2KNO3 → N2 + 5Na2O + K2O
3. 2K2O + SiO2 → K4SiO4
2Na2O + SiO2 → Na4SiO4
In the first reaction, sodium azide is ignit-
In the second reaction, the sodium is
reacted with potassium nitrate, releasing
more nitrogen and two more dangerous
oxides that must be neutralized. The final
stage involves the reaction of potassium
oxide and sodium oxide with silicon dioxide to produce silica glass. Until an airbag
is completely neutralized, it is an environmental hazard and must be handled with
caution.
Airbags are set to deploy at a minimum of
30km/hr, a speed that could cause significant injury if a passenger was not wearing
their seat belt, but unlikely to cause serious injury if properly belted in.
If a vehicle is involved in a minor crash,
the cost of repairs is likely to be 50%
Airbags: Is there a price limit on safety? – Page 2
In conclusion, it seems clear that airbag
technology has resulted in fewer fatalities
from high-speed collisions. New advances
are making their deployment safer all the
time. However, safety comes at a cost,
including higher rates for insurance,
injury on inflation and environmental
concerns with disposal.
Review Questions:
1. What are some of the disposal concerns for detonated and intact
airbags?
2. Should passengers have the option of
turning off airbags at their discretion?
3. Current deployment speed is set to
around 30 km/hr. Given the high
costs of repairs & insurance, is this
set too high or too low?
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Cost of Repairs
PARTS
QTY
DESC.
UNIT PRICE-
1
1
1
1
1
1
1
1
1
1
8
2
1
1
1
1
1
1
NPC
NPC
NPC
NPC
NPC
NPC
NPC
NPC
WOODSTO-CK
WOODSTO-CK
NPC
NPC
COREYS
COREYS
CRSS
CROS
NPC
NPC
REBAR
AIRBAG
AIRBAG
AIRDAM
C/SPRING
HOSE
A/C LINE
GRILLE
RADIATOR
CONDENSOR
FREEZE
BULBS
DASH
COLUMN
HEADLIGHT
FASCIA
PRETENSIO
PRETENSIO
$332.00
$865.00
$670.00
$49.00
$70.50
$10.05
$117.00
$161.00
$180.00
$180.00
$2.88
$7.50
$600.00
$300.00
$205.61
$357.10
$92.25
$147.00
$332.00
$865.00
$670.00
$49.00
$70.50
$10.05
$117.00
$161.00
$180.00
$180.00
$23.04
$15.00
$600.00
$300.00
$205.61
$357.10
$92.25
$147.00
TOTAL - PARTS
TOTAL - SUBLET
$4,374.55
$262.95
TOTAL - SUPPLIES
TOTAL - LABOUR
SUBTOTAL:
TAXES:
TOTAL:
$198.00
$5.00
$203.00
$2,061.00
$6,901.50
$966.21
$7,867.71
1 BODY SHOP MATERIALS
1 HAZARDOUS WASTE
Airbags: Is there a price limit on safety? – Page 3
$865.00
$670.00
$49.00
$600.00
$300.00
$2,484.00
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Student Worksheet
Airbag Chemistry
When an airbag explodes, there are 3 different types of
reactions that occur. Sodium azide produces nitrogen
gas but there is a bi-product of Na. Na is very reactive
and must be neutralized. For this, potassium nitrate is
used. This creates two further compounds, sodium oxide
and potassium oxide which must be neutralized by silicon dioxide.
Chemical reactions:
1 Sodium Azide is ignited. Nitrogen gas fills nylon bag
at 150-250 miles/hr
NaN3 → N2 + Na
2. Sodium is very reactive and must be neutralized.
Using the number of moles of Na produced from the
first reaction, calculate using stoichiometry,
Na + KNO3 → N2 + Na2O + K2O
a) how many moles of Na2O are created?
b) how many moles of K2O are created?
2
Reaction with potassium nitrate (1st stage to eliminating dangerous by-products)
Na + KNO3 → N2 + Na2O + K2O
3. These products Na2O + K2O are also dangerous, and
must further be neutralized by SiO2 to produce
K4SiO4 and Na4SiO4
3
Reaction with sodium and potassium oxide to form
silicate glass (2nd stage to eliminating dangerous
by-products)
K2O + SiO2 → K4SiO4
Na2O + SiO2 → Na4SiO4
a) What mass of SiO2 would be required in order to
fully react with all of the of K2O from part (2)?
K2O + SiO2 → K4SiO4
A typical 60L airbag requires 5.82 moles of nitrogen gas
to fill it up. A manufacturer puts 65g of SiO2 in an airbag.
Using stoichiometry, we are going to find out how many
grams of SiO2 is required to completely neutralize the
dangerous by-products of the airbag reaction & conclude whether 65 g is enough.
1. Use stoichiometry to calculate the number of moles
of sodium produced by the first reaction if 378.3g of
NaN3 is used. (Balance the equation first):
NaN3 → N2 + Na
Airbags: Is there a price limit on safety? – Page 4
b) What mass of SiO2 would be required in order to
fully react with all of the of Na2O from part (2)
Na2O + SiO2 → Na4SiO4
4. How much SiO2 is needed in total? Was 65 g of SiO2
enough?
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Teacher answer sheet
Airbag Chemistry (Solutions)
1. Use stoichiometry to calculate the number of moles of
sodium produced by the first reaction if 378.3g of
NaN3 is used. (balance the equation first):
NaN3 → N2 + Na
a) What mass of SiO2 would be required in order to
fully react with all of the of K4SiO4 from part (2)?
K2O + SiO2 → K4SiO4
2K2O + SiO2 → K4SiO4
2NaN3 → 3N2 + 2Na
if 378.3g of NaN3 was used then 5.82 mol Na was
produced.
Ratio of 2NaN3 : 2Na is , thus 2/2*5.82 = 5.82 mol Na was
produced by this reaction
2. Sodium is very reactive and must be neutralized.
Using the # of moles of Na produced from the first
reaction, calculate using stoichiometry,
Na + KNO3 → N2 + Na2O + K2O
10Na + 2KNO3 → N2 + 5Na2O + K2O
a) how many moles of Na2O are created?
5/10*5.82 = 2.91
1
*0.58 = 0.29
2
0.29 mol * (28.09+16*2)
.29*60.06
17.42 grams of silicon dioxide
(b) What mass of SiO2 would be required in order to
fully react with all of the of Na4SiO4 from part (2)
Na2O + SiO2 → Na4SiO4
2Na2O + SiO2 → Na4SiO4
1
2 *2.91 = 1.46
1.46 mol * (28.09+16*2)
1.46*60.06
87.39 grams of silicon dioxide
(b) how many moles of K2O are created?
1/10*5.82 = 0.58
4. How much SiO2 is needed in total?
87.39+17.42 = 104.81 grams of silicon dioxid.
3. These products Na2O + K2O are also dangerous, and
must further be neutralized by SiO2 to produce K4SiO4
and Na4SiO4
Airbags: Is there a price limit on safety? – Page 5
Volume 39 • 2 November/December 2007