Airbag tech im­proves, but not per­fect

Winnipeg Free Press - Section F - - AUTOS - JIM KERR

AIRBAG tech­nol­ogy con­tin­ues to im­prove with ev­ery new ve­hi­cle in­tro­duced. Since the in­tro­duc­tion of driver’s side airbags, au­tomak­ers have added pas­sen­ger front airbags, side airbags, knee airbags, side cur­tains and seat-belt pre-ten­sion­ers.

Here’s what’s new and how the tech­nol­ogy works.

Most airbags still use py­rotech­nic charges to trig­ger in­fla­tion. A small ig­niter starts sodium azide burn­ing, which pro­duces ni­tro­gen gas. This gas in­flates the airbag. A white pow­der cre­ated by the chem­i­cal re­ac­tion may ir­ri­tate skin, but most pow­der af­ter an airbag de­ploy­ment is just corn starch or tal­cum pow­der packed with the airbag to lubri­cate it as it opens up.

Some airbags are in­flated by a com­pressed-gas cylin­der. An ex­plo­sive charge punc­tures the end of the cylin­der, al­low­ing the gas into the airbag. Heat from the charge helps the gases ex­pand so the airbag de­ploys quicker.

The time from when crash sen­sors de­tect an im­pact un­til the airbag is in­flated is mea­sured in thou­sandths of a sec­ond. High-speed cam­eras are needed to catch an airbag in­flat­ing. It oc­curs so quickly that even our eyes can­not see it hap­pen­ing.

Ve­hi­cle oc­cu­pants can be hurt by airbags. One of the most com­mon in­juries is fric­tion burns from the high speed of the airbag ma­te­rial rub­bing against a per­son as it de­ploys. If there are ob­jects be­tween the airbag and a pas­sen­ger when the airbag de­ploys, th­ese ob­jects can strike the pas­sen­ger with tremen­dous speed. Driv­ers should place their hands on the steer­ing wheel in the 3 and 6 o’clock po­si­tions to re­duce the pos­si­bil­ity of their hands strik­ing them in the face. Pas­sen­gers should be sit­ting in a com­fort­able up­right po­si­tion. I shud­der when I see pas­sen­gers rid­ing with their feet on the dash. Their knees could pack a hor­rific punch!

To re­duce the pos­si­bil­ity of in­jury from front airbags, man­u­fac­tur­ers have “de-pow­ered” them in the last few years. Less force­ful in­fla­tion rates are still de­signed to pro­tect in most sit­u­a­tions, but some man­u­fac­tur­ers chose to use two-stage airbags that will in­flate with less force or more force de­pend­ing upon sen­sor in­puts and ac­ci­dent con­di­tions.

One re­sult of two-stage airbags is that the airbag may still be charged af­ter an ac­ci­dent al­though it has al­ready in­flated. Even in­flated airbags should be han­dled as if they could go off.

Side airbags are usu­ally lo­cated in the sides of the seats, al­though some are lo­cated in the side doors. Some man­u­fac­tur­ers use spe­cial sen­sors on side airbag sys­tems. Honda has po­si­tion sen­sors in the side of the pas­sen­ger bucket seat that will pre­vent the side airbag from de­ploy­ing if the pas­sen­ger is in the wrong po­si­tion. Jaguar has used ul­tra­sonic sen­sors to help de­ter­mine pas­sen­ger po­si­tion be­fore de­ploy­ing airbags. Seat-track po­si­tion sen­sors are also used in some ve­hi­cles to de­ter­mine airbag de­ploy­ment force.

Side cur­tain airbags are com­mon in many ve­hi­cles, es­pe­cially SUVs, CUVs and crew-cab pick­ups. BMW, Mercedes, Volvo and Ford are just a few of the man­u­fac­tur­ers us­ing airbags that cover the side win­dows, pro­tect­ing he heads of oc­cu­pants dur­ing side im­pacts and rollovers. SUVs such as the Ford Ex­plorer and Volvo XC90 keep the side cur­tains de­ployed for up to six sec­onds if a rollover oc­curs, com­pared to only a frac­tion of a sec­ond for front airbags.

Seat­belts are an in­te­gral part of airbag sys­tems. They hold us in the proper po­si­tion for airbags to work. Some man­u­fac­tur­ers are us­ing seat­belt pre-ten­sion­ers, which are ex­plo­sive charges that pull the seat­belts tight around the occupant just be­fore an airbag is de­ployed. This seat­belt must be re­placed af­ter the pre-ten­sioner has been ac­ti­vated.

Man­u­fac­tur­ers are be­gin­ning to build “an­tic­i­pa­tion” into their sys­tems such as the Mercedes Pre-Safe. Stud­ies show that most im­pacts are pre­ceded by a few sec­onds of re­ac­tion by driv­ers. The Pre-Safe sys­tem senses the driver’s re­ac­tion and ve­hi­cle move­ment to pre­dict an im­pact. It then closes the sun­roof, moves the pas­sen­ger seat to the op­ti­mum po­si­tion and ten­sions the seat­belts with re-use­able pre-ten­sion­ers to hold oc­cu­pants in po­si­tion be­fore the im­pact oc­curs.

Some airbags use seat sen­sors to de­ac­ti­vate the sys­tem if no­body is sit­ing in the seat. This re­duces re­pair costs if there are no pas­sen­gers in the ve­hi­cle.

Airbags are de­signed to help pro­tect us dur­ing life-threat­en­ing ac­ci­dents, but they’re not the per­fect an­swer. Seat­belts, alert driv­ers, and good ve­hi­cle con­di­tion are still the best safety fea­tures we have. Jim Kerr is a me­chanic, in­struc­tor of au­to­mo­tive tech­nol­ogy, free­lance jour­nal­ist and mem­ber of the Au­to­mo­bile Jour­nal­ists’ As­so­ci­a­tion of Canada.

Gen­eral Mo­tors in­tro­duced the first front cen­tre airbag last year.

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