For the first time the federal government has issued a regulation to protect people from the safety systems in their cars. Besides assuring that airbags will continue to prevent deaths and injuries in serious crashes, the new standard for occupant protection is designed to make airbags safer for out-of-position occupants.
Airbags already have saved thousands of lives. But inflating airbags have killed about 160 people in relatively low-severity crashes in which serious injuries otherwise would have been unlikely. Plus airbags have caused some deaths and injuries to out-of-position (predominantly unbelted) people in higher severity crashes. Indications are that newer airbag designs and efforts to educate motorists are reducing these problems. The number of airbag deaths appears to be shrinking even as the number of airbag-equipped vehicles increases.
Under consideration for almost two years, the new rule follows a Congressional mandate to improve the protection offered by airbags and minimize their potential to cause harm (see "Advanced airbags are the focus of new NHTSA rulemaking," Oct. 10, 1998). Never before have automakers had to meet such extensive testing requirements.
But the government isn't closing the book on airbag rulemaking. The National Highway Traffic Safety Administration (NHTSA) says it plans research on a few points it considers to be unresolved, including the controversial issue of the maximum speed of rigid-barrier crash tests using unbelted dummies.
Until now, the only dummy required in government airbag tests has been the 50th percentile adult male. Now tests with dummies representing children of various ages and short-stature women will be required.
The 5th percentile adult female has been added to almost all of the crash tests. This dummy also will be used in static tests for out-of-position occupants, which don't involve crashes. Dummies representing children ages 1, 3, and 6 have been added exclusively for static testing and won't be required in any crash tests.
The static tests require either suppression of airbags or inflation with forces that result in dummy injury measures below specified thresholds. This is intended to reduce the dangers of inflating airbags to those most at risk — children and short adults. Of the 162 airbag deaths in low-severity crashes confirmed by NHTSA, 96 were children and at least 22 were relatively short women.
Tests to improve protection
In the past, airbag rules specified crash tests into rigid barriers, both perpendicular and at a 30-degree angle, at speeds up to and including 30 mph. These tests have required unbelted and belted 50th percentile adult male dummies. Since 1997, a sled test has been permitted as an alternative to rigid-barrier tests with unbelted dummies.
Rigid-barrier impacts carry over in the new standard. But the maximum speed of 30 mph has been changed to 25 mph for the tests with unbelted dummies, and now such tests will be required for both small female and average-size male dummies. The oblique (30-degree) version of the unbelted barrier test will be required with males only.
The test speed for belted dummies will increase to a maximum of 35 mph starting in 2007, after the rest of the requirements have been fully phased in. This change applies only to male dummies. Some time in the future NHTSA intends to propose the same increase for small females.
The maximum speed of rigid-barrier tests with unbelted dummies prompted intense debate. The final rule eliminates the sled option that had allowed initial depowering of airbags. But instead of returning to the requirement that the unbelted dummy injury criteria be met at speeds up to 30 mph, the new standard specifies rigid-barrier tests from 20 to 25 mph for unbelted dummies. Setting the minimum at 20 mph, instead of 0 mph as in the previous rule, is intended to ensure that automakers aren't inappropriately required to set airbag deployment thresholds too low.
Improving crash sensors
In each of the standard's rigid-barrier crash tests, vehicle front ends hit an unyielding barrier in a perpendicular or oblique impact. The new rule adds a completely different kind of test to the matrix — an offset frontal deformable barrier test using a small female driver dummy.
The impact of 40 percent of the test vehicle's front end into a yielding barrier (impact on the driver side) better approximates some vehicle-to-vehicle crashes. The requirements of this test must be met in the speed range of 0 to 25 mph, replicating the problem that relatively low-speed offset crashes pose for some airbag sensors — the softer "crash pulses" can make it harder to determine whether or when airbags should deploy.
Minimizing the risk of harm
For passenger airbags, the new rule allows manufacturers either to suppress the airbags whenever children are present (static suppression) or to deploy airbags without exceeding the dummy injury criteria (low-risk deployment). This covers infants and children in the front seat, whether or not they're properly secured in a child restraint or booster seat.
The static suppression tests are extensive. When they call for the use of a child restraint, the vehicle must be able to certify using any of the nearly two dozen child restraints specified in the regulation. Each restraint must be tested in multiple positions, both with and without vehicle safety belts and universal child restraint anchors attached. The sensors used for airbag suppression must be able to detect children positioned directly on the seat in numerous ways — sitting down without a seat belt, standing up, kneeling, and lying down on the seat. An airbag system that successfully deactivates for a child dummy also must demonstrate it doesn't deactivate for a small adult female.
In tests demonstrating low-risk deployment for infant and child passengers, airbags must deploy without significant injury risk in at least two potentially dangerous situations — for example, with a child dummy's head resting against the instrument panel and then, in another test, with the dummy's chest against the panel. Neck and head injury measures on the dummy must stay within established limits. A crash isn't required for the test itself, but a low-speed crash must be conducted beforehand to determine what airbag inflation level (if there's more than one) will be deployed.
Low-risk deployment tests also are an option on the driver side. Similar to the low-risk deployment test for children, this option specifies that the small adult female dummy is sitting forward in the seat and contacting the steering wheel when the airbag deploys. The new rule doesn't allow for suppression of the airbag on the driver side merely because a driver is present in the seat.
For the female dummy on the driver side and for the three- and six-year-old dummies on the passenger side, automakers can choose to meet a third alternative — dynamic suppression. A dynamic system would suppress an airbag when an occupant moves into a zone where inflation injury becomes likely. Multiple dynamic suppression technologies are in development, so rather than specify procedures NHTSA has proposed expedited rulemaking for any automaker wanting to introduce such technology.
New injury criteria
The head, neck, chest, and leg injury criteria developed for the small adult female and child dummies are based on those previously developed for the average-size adult male dummy. A few of these injury measures have been further refined.
NHTSA's proposed new way of computing the head injury criterion (HIC) uses a lower threshold and a shorter time interval. The current standard specifies that the HIC value for the 50th percentile male dummy in rigid-barrier tests must not exceed 1,000 during an interval of 36 milliseconds. The new maximum HIC will be 700 over 15 milliseconds for the adult male and female dummies and for the 6-year-old child. This change doesn't make the requirement any more or less demanding but simply makes the measure more consistent with the biomechanics of head injury. Lower HIC values will apply for the smaller child dummies.
NHTSA has adopted separate limits on chest acceleration and deflection to measure potential chest injuries for all dummies except the one representing an infant, to which chest injury criteria don't apply. Chest deflection limits, which measure the compression of the chest relative to the spine, have been lowered and made more stringent. A 60 g chest acceleration limit will continue to apply for adult male and female dummies. A slightly lower limit has been adopted for the others.
Nij is a relatively new injury measure that accounts for flexion, extension, tension, and compression in the neck. Unlike separate limits for each of these forces, Nij accounts for the superposition of loads and moments and the additive effects on injury risks.
Making the transition
Advanced airbags meeting the new standard will be required starting with 2004 model vehicles. Automakers will be required to certify an increasing percentage of their fleet each year, and all new vehicles must comply after August 2006. Starting in 2007, an increasing percentage of all new vehicles will have to pass the rigid-barrier crash test with belted male dummies at 35 instead of 30 mph — a requirement that will be fully implemented by 2010.
NHTSA originally planned to phase in the new requirements starting with 2003 model year vehicles. With the number of new requirements, it now considers the additional lead time essential.
The strength of the new standard is that it will require minimum levels of protection for unbelted and belted occupants in high-speed crashes and at the same time reduce the risks of airbag-induced injuries to out-of-position occupants. It's important to recognize, however, that it will not guarantee inflating airbags pose no risks. New required warning labels in vehicles convey a similar message.
Summary of new test dummies, injury criteria
Besides a plethora of new tests (see below), the airbag standard issued recently calls for four new test dummies in addition to the average-size (50th percentile) adult male already used in airbag testing:
- Small (5th percentile) adult female
- 6-year-old child
- 3-year-old child
- 1-year-old infant
Some measures of injury likelihood also will change or expand:
- Pelvis/upper leg injury criterion unchanged (10 kN)
- Chest acceleration measure unchanged (60 g)
- Chest deflection will change from 76 mm to 63 mm
- HIC will change from 1,000 over 36 ms to 700 over 15 ms
- Neck injury measure (Nij) will be added
New test requirements