SEATING: Crash testing

By: Steve Skinner


Australia's developed its world-leading standard for the safety of coach seats and seat belts

SEATING: Crash testing
A crash test dummy sits in the popular Transport Seating Safe-t-Ride low back coach seat, designed by industry identity Rod Ferguson for school and charter buses

It was 1989 and seat belts in coaches were unheard of, as were any sort of crash standards for seats and their anchorages.

However, Australian authorities were in the process of harmonising with European coach crash standards.

Then the horrific Grafton and Kempsey bus crashes happened within a couple of months of each other, both on the Pacific Highway in New South Wales.

Near Grafton a coach and a truck collided head-on at 100km/h, killing 20 people. At Clybucca near Kempsey two coaches hit head-on at full speed, killing 35.

"They didn’t have seat belts in buses in those days – they didn’t exist, and the anchorages were pulled out of the floor," NSW Roads and Maritime Services Crashlab Manager, Ross Dal Nevo says.

Back then Dal Nevo, a mechanical engineer by trade, found himself in the thick of urgent testing and analysis at Crashlab, since developed into a $20 million crash testing facility in Sydney’s west.

Dal Nevo and his colleagues concluded that the proposed European standard, ECE 80, wouldn’t have made much difference in the Pacific Highway crashes or several other bad crashes around the same time.

For one thing, ECE 80 only tests for 10 g, i.e. a forward crash force equivalent to 10 times the force of gravity – 10 times the downward pressure of someone sitting in a seat.

However, the Grafton and Kempsey crashes had what were estimated to be 20 g decelerations, "which means your body takes on the effect of 20 times your normal weight when it hits the seat in front," says Dal Nevo, adding that car seats and belts are designed to withstand 30 g crashes.

"As incredible as that 20 g-force is, it’s survivable," he says.

Another problem with the European standard is it’s a ‘static’ test - i.e. bus seats are loaded with hydraulic rams – rather than being a ‘dynamic’ test i.e seats crashing into something with much quicker and different force. 

Out of the Australian carnage arose Australian Design Rule 68, assuming crash forces of 20 g and involving a dynamic test.

ADR68 sets a mandatory standard for seats, anchorages and three-point seat belts in coaches, but controversially, not school buses operating at highway speeds.

All new Australian and imported coaches built from July 1995 have had to comply with ADR 68, which still leads the world in its crash test toughness.

"Thankfully there haven’t been crashes like Grafton and Kempsey to really tell us how effective ADR 68 has been," says Dal Nevo.

"But there have been crashes, and generally when people aren’t injured or killed, they’re not headline news – where they’ve been wearing seat belts in these crashes, the results have been positive."

TEETHING PROBLEMS

In the early days there was industry resistance to the new rules.

A 2004 review paper says bus operators and manufacturers were initially critical of the proposed ADR, citing feared cost and weight penalties. The paper adds that coach seat manufacturers were initially reluctant to take up Crashlab’s offer of free testing of prototype seats.

But that’s all ancient history now.

"One of the biggest concerns for industry was they thought the seats would have to be so much bigger and heavier and stronger to withstand the forces," Dal Nevo say.

"They said if the seats get heavier you lose capacity, because the bus can only carry so much weight.

"But ironically they are actually producing lighter seats than the old ones they’re replacing that didn’t have seat belts on them. They are lighter but stronger, made with a lot more engineering and science."

Modern seats are not significantly more expensive.

Crashlab estimates that in the past 10 years it has tested about 30 new seat models from about five manufacturers, mainly Australian.

"Most of the work would have been done back in the mid-90s when the ADR was being introduced – we were testing bus seats all the time," Dal Nevo says.

These days now that industry has extensive experience with the ADR, each seat anchorage test costs $6,500 and each occupant injury test $12,500. They are usually done at the same time, so it pays the coach and seat manufacturer to get it right first time.

There is at least one other accredited bus seat testing facility in Australia -- APV Engineering and Testing Services in Melbourne.

NUTS AND BOLTS AND FLEXING

The importance of secure anchorages is obvious, and so too is the importance of passengers being belted in, so they are not thrown around.

However, seat belts and seats themselves involve more subtle design and assessment.

"In a crash, despite the fact you are restrained by a seat belt, you are still going to push forward," Ross Dal Nevo says.

"So you are going to make knee contact to the seat in front of you, and then some time later your upper torso is going to push against the upper part of the seat belt and you’ll lean forward.

"Now you might ask is the seat belt working? Well yes it is because seat belts aren’t rigid like a steel band otherwise they would cut you in half. A seat belt is actually designed to have a controlled amount of stretch, to be able to take the impact energy away from you.

"Things that are rigid aren’t good in terms of getting rid of crash energy."

That applies to seats themselves, which have to be capable of what Dal Nevo describes as ‘controlled flexing’. It’s a similar energy absorption rationale to the ‘crumple zone’ in the front of a car.

"If the bus seat in front of you also has a restrained person, both seats flex forward, so you tend to move in unison and maintain the gap," Dal Nevo says.

"However, if that seat is empty, it doesn’t flex forward as much, and chances are you will strike it. That’s why it’s important that the seat back has padding in it, and hasn’t got big steel bars running across the back of the frame where your head is going to hit."

The worst-case scenario is where a seat-belted passenger has an unrestrained passenger behind him or her, and an empty seat in front.

That’s because the passenger behind is going to push the middle seat further forward than is necessary for controlled flexing, but the front seat won’t move as much – so the middle passenger, even though he or she is belted in, is far more likely to hit their head hard on the front seat.

"This is the injury criteria test, where the instrumented crash test dummy says ‘That was an acceptable impact in terms of not killing me or permanently injuring me’," says Dal Nevo.

This worst-case scenario has to be tested for, because as Dal Nevo says: "Buses aren’t always full and people don’t always do the right thing".

To that he could add that unlike on planes, there are no hosties walking up and down the aisle to check that everybody has their seat belt on before departure.

TOUGH LIFE FOR A DUMMY

Needless to say, the instrumented dummies worth about $250,000 cop a hammering during each test.

They sit in an individual seat or a seat module provided by the coach and seat company, which is attached to the Crashlab ‘sled’.

The sled is wound back like a rock in a sling-shot, using thick ‘bungee’ cords. When the sled brakes are released, the sled rockets forward at 25km/h, and then a piston bounces it back at the same speed.

The net effect is the same as an instantaneous stop in a head-on crash into a rigid wall at 50km/h. This is equivalent to a 20 g crash.

The dummies have instrumentation in them to monitor impacts to the head, chest and knees. The information from the collision – which takes just milliseconds – is conveyed through what seems like kilometres of wiring to the central computer. The whole process is also photographed.

Ross Dal Nevo doubts there are many pre-1995 highway coaches out there which pre-date the benefits of this life-saving technology and testing.

For a start, they’d be nearly 20-years-old now. Second, "the manufacturers picked up very early in the piece that it was good marketing and good practice to have their coaches all fitted with compliant seat belts".

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