Friday, March 23, 2007

Hidden Roll Bar Protection Potential Hazard for Fire and Rescue?

Q: An individual involved in a rollover accident in a "3 class BMW convertible" relayed that after the accident, there were two tubes sticking up from each seat, acting as roll bars, that were not exposed when first arrived at the scene. Has anyone heard of such a hidden roll bar system? Would this be a potential hazard to rescue personnel similar to non-deployed airbags?

A: There are currently two types of automatic roll-bars (RPS/ROPS). A pop-up model that is mounted behind the occupant seat and a second type that flips up to look much like a conventional flat roll-bar. These have been on the production line for some time, but with little publicity until now.

BMW Rollover Protection System (RPS) that you are asking about can be seen on the BMW E36 Convertible. This is a spring loaded unit which is mounted directly behind each rear seat headrest. Unlike Volvo and BMW, which are using a mechanical spring loaded deployment, both Mercedes pop-up and flip-up systems are hydraulically deployed. The Mercedes pop-up system has a single bar with two "U" shaped bends which extend up through two openings. The Volvo and BMW are two separate cassettes.

The RPS/ROPS is activated by an inclinometer to sense vehicle inclination and lateral acceleration. There is a G-sensor to sense vehicle weightlessness also.

The system will deploy when the control module senses any of the following:

- When the vehicle approaches a lateral angle limit of 62 degrees.

- When the vehicle experiences a lateral acceleration of approximately 3 Gs.

- When the vehicle approaches its longitudinal angle limit at approximately 72 degrees.

- When a combination of longitudinal acceleration and longitudinal angle would cause the vehicle to roll over in the forward direction.

- When the vehicle becomes airborne and achieves weightlessness for at least 80ms.

The control module senses the above (except for weightlessness) by means of the inclinometer built into the control unit. If the vehicle is tilted or accelerated enough, the air bubbles in one of the tubes in the inclinometer pass by a LED. A photo transistor mounted across from the LED senses a change in density of the liquid when the bubble crosses the beam. It then sends a signal to the processing chip. The Volvo/BMW control unit will then send a signal to the actuator solenoids on each of the two separate cassettes. This releases the restraining catches and the roll bars will spring upward.

As with the SRS, the backup power supply capacitors allow the system to function even if the vehicle power is interrupted in an accident. The Volvo RPS has a reserve power unit which will store a charge for 5 seconds.

Both types of RPS will deploy between 2 and 3 tenths of a second!! Once the sensor in the vehicle predicts the car to be in a rollover situation, the bars will deploy. They may also be deployed by the driver (Mercedes) using a manual switch on the dash. The RBS may also be interconnected to the airbag system. De-energize the electrical system as soon as possible, including any device such as GPS, cell phones and alarm systems which may back feed the SRS.

A dangerous point to remember is that they look harmless and blend in with the interior of the car's color scheme. Perhaps the best way to avoid injury to a rescue worker is to manually deploy the roll-bar in a controlled situation. Mercedes' have an electric switch which can slowly (approximately 4 seconds) raise or lower the roll-bar. The Volvo mechanics that have been trained in the system can manually deployed the roll-bar using a long handed straight screw driver. The BMW can be activated by a tester or MoDiC; there is an access hole for trained personnel to manually activate the system.

Some systems can be locked out using a computer. When transported the Volvo convertible ROPS is deactivated at the factory, the dealer uses a computer to reactivate the system.

For rescuer holding traction for a C-spine injury, the rescuer would normally assume a position behind the patient. This now put the path of deployment in the neck head area of the rescuer! I measured the distance for a Mercedes and that was approximately 10 inches from the deck to the top of the pop-up roll bar, the Volvo roll-bar extends 20 inches - once deployed they have to be manually reset, this will allow you to safely work behind the patient. When in doubt if the bar has been deployed, keep a proper safe working distance. This goes for any supplemental restraint device.

The pop-up type has a protective plastic cap that snaps on a "U" shaped bar. The flip-up type is padded and folds down to wrap around the rear deck. It blends in perfectly and you might assume it to be just part of the plastic trim to the fabric top.

I have co-authored an emergency guideline for airbags and automatic roll-bars to be used for rescue personnel. IT was published on the Internet by Emergency Grapevine Magazine. You may find it by going to the following link:

There will be a picture of a Mercedes CLK with the pop-up type roll-bars. Your local dear for BMW, Volvo and Mercedes should be more than happy to show you these new devices and perhaps deploy them. Specific information on RPS/ROPS is available in technical references from the manufactures.

As we make safer cars for the occupant, we also increase the risk to emergency service personnel. If you don't have a dealer near by I will be glad to send you a jpg of both types of automatic roll-bars.

Ron Shaw
Plymouth, MA

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