Automotive "Black Boxes"? Explosives in your car?

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January 17, 2008

Yes, and yes.

Many an RVer is driving around right now with “Big Brother” watching, and up to six explosive devices in their vehicles.

For years, aviation crash investigators have had the benefit of being able to recover some of the last moments of a doomed flight by recovering and analyzing the flight data recorder. This device, commonly referred to as a “black box” (which is actually bright orange), saves data on altitude, speed, and control inputs. Unknown to many, this type of information is available to automotive crash investigators as well.

First, a little background. In the early 1970’s, the US National Transport Safety Board recommended that vehicle manufacturers and the National Highway Traffic Safety Administration (NHTSA) work together to gather crash data using some kind of on-board recording device. General Motors has become a leader in making this information accessible to a person with the right equipment and knowledge. Some type of recorder has been installed in General Motor’s vehicles since 1974. It began with airbag-equipped vehicles having old fashioned electromechanical g-sensors, diagnostic circuits, and an instrument panel readiness light that illuminated if a fault was detected. These crude sensors basically amounted to a metal ball in a tube. At one end of the tube was a magnet, on the other, two contact wires separated by a gap. If the impact was severe enough to dislodge the ball from the magnet, the sensor was triggered.

In 1990, a more sophisticated Diagnostic and Energy Reserve Module (DERM) was introduced that could record closure times for the sensors, as well as any fault codes present at the time the airbags were deployed. In 1994, another revision was done, and the Sensing and Diagnostic Module (SDM) was introduced. This unit had the ability to calculate and store the change in velocity the vehicle experienced during the crash event. The SDM also featured the ability to record the state of the driver’s seatbelt (buckled or not) and the same information in “non-deployment” events. Non-deployment events are changes in longitudinal (front to back) velocity that cause the airbag system to “wake up”, but are not severe enough to cause the airbags to deploy. An example of such an event would be a minor to moderate collision, or hitting a large pothole. A later SDM revision in 1999 added more parameters being stored, among them things like: engine RPM, vehicle speed, brake circuit switch status (on or off), and throttle position – all for up to 10 seconds (or more – as you’ll see later) prior to the crash. These devices are referred to as Event Data Recorders (EDRs).

Newer designs even have what I call “early warning” sensors at the front of the vehicle. Since the sensing module is generally mounted in close proximity to the passengers (it is the forces the passengers are experiencing that we want to monitor after all) it takes precious milliseconds for the crash pulse to reach those sensors. The early warning sensors (referred to as a “discriminating sensors”) are mounted at the front of the vehicle and give an advance warning of an impact as it happens.

These are extremely advanced electronic devices, and they do the job of measuring a gamut of parameters, determining if one or more pyrotechnic (explosive) devices need to be deployed, deploying those devices, and they do it all much faster than you can blink. Some newer vehicles even keep track of things like how tall or short the driver is, and will adjust the power of the deploying airbag accordingly. They do this by measuring where the driver’s seat is in the seat track it slides on when you adjust it. The system also changes the threshold for when a deployment is commanded based on if the passengers are wearing their seatbelts or not. Never buckle your seatbelt if you’re not in it. It is dangerous to “fool” the system into thinking you’re wearing your seatbelt when you’re not.

Now, about those explosives… Seatbelt pretensioners and airbags are all activated by explosive chemical reactions. The chemical inside most airbag deployment motors is sodium azide. When this chemical is exposed to an electrical current, it reacts (explodes) and releases nitrogen gas. It is this gas that fills the airbag and allows it to cushion the impact. Seatbelt pretensioners work in a similar fashion. If the EDR senses a crash is occurring, it will fire the pretensioners to take the slack out of the seatbelt, and properly position the occupant so the airbag can do it’s job. The EDR may deploy just seatbelt pretensioners without commanding an airbag deployment depending on the severity of the crash and other parameters it measures.

The EDR records an event whenever there is a non deployment or a deployment of the vehicle’s airbags. Sometimes the data can be overwritten, in other cases; it is saved permanently on the module.

So, how is all this data accessed? It can be extracted one of two ways. If the vehicles electrical system is intact, a cable can be plugged into the diagnostic port (the same one your mechanic uses), and the data can be downloaded into a laptop computer. If the vehicle’s electrical system has been damaged in the collision, the EDR can be removed from the vehicle and downloaded at a later time. Alternatively, the vehicle’s manufacturer can download and return the information from an EDR at the request of a Collision Investigator, but there are many stipulations; and lawyers working for the manufacturer look at each case before data is released.

In a recent case I dealt with, a major auto manufacturer downloaded data out of the ECM of a 2004 pickup truck and I received 400 seconds (more than 6 minutes!) of pre-impact driving. Speed, throttle inputs, brake inputs, all broken down second by second. It was the knock out blow dealt by the Crown prosecutors in the case against the alcohol impaired driver. He had disobeyed a stop sign on an urban street while traveling at nearly 60 miles per hour in a zone posted for 30 miles per hour. He will spend the next several years in prison for forever altering the quality of life of a passenger in the vehicle he struck at that intersection.

Another case that comes to mind where I used this technology involves a collision of a 2004 GMC 2500HD 4×4. It had been in a repair shop for some work, and local fire regulations require that the keys be left in vehicles that are being stored inside the repair facility. A local person on the wrong side of the law broke into this shop in the middle of the night. He discovered the keys in the vehicle, and promptly opened the overhead door and let himself and his newly acquired truck out. He made it about a half mile down the street, and failed to negotiate a gentle curve in the roadway. He left the roadway, careened through a gas station parking lot, narrowly missed the huge LPG filling station tank, went through a fence, and into the side of a brick building. The truck ended up embedded in the wall, and started on fire. A good Samaritan saw the collision, and dragged the seriously injured driver/suspect out of the truck before he was consumed by the flames. I was called to piece the whole thing together. There was precious little roadway evidence to use, as the driver was very drunk at the time, and his attempt to negotiate the curve was feeble. The box that contained the electronic data had been exposed to some serious heat, but surprisingly, still recorded the data. I was able to determine the vehicle had been traveling almost 80 miles per hour before impact. The street this happened on is posted as 30 miles per hour. Without the EDR download, I would have had a very difficult time coming up with an accurate speed. The driver died a few days later in hospital, so it was a bit of a lost effort anyway.

We as RVers need to be aware this technology exists and can be recovered. Some drivers may balk at the fact that their driving is being recorded, assuming that this data can only do legal harm to a motorist involved in a collision. We must remember however, that it can also show that a driver was driving within the limits of the law and common sense as much as it can show he wasn’t.

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  1. ib516

    Yes, I typically get a search warrant to download the data, but I also access it by written permission as well, such as was the case with the stolen truck driving into the building. The bad guy has no “expectation of privacy” in that case as it wasn’t his truck.

  2. The Texan

    I notice that you are in Canada, which must have very different laws about accessing this “black box”, than does the US. In the US, unless the Insurance Co has required you to waive your right of ownership to the box, which some do, they are prohibited from accessing the information during an investigation, except by court order. The Police are required to get a search warrant in order to access the information, as the box is owned by the vehicle owner, and this includes leased vehicles. Yes it is used by both the Insurance industry and the Police, but with supposedly tight controls.