Fire-Service-Rescue-and-Extrication

SUBJECT: Electrical Hazards at Vehicle Rescue Incidents

TOPIC: High-Intensity-Discharge(HID) Headlights

OBJECTIVE: Understand the design and operation of high-intensity-discharge headlights and appropriate responder actions to complete when working near these units.

TASK: Given the scenario of a vehicle collision with injuries, explain procedures for responders to complete to eliminate the electrical hazard risk presented by high-intensity-discharge headlights.

High-intensity-discharge (HID) headlights, those bright, slightly bluish-looking headlights that we see on vehicles at night, use an inert and highly pressurized xenon gas to produce their brilliant light. Xenon is an odorless, colorless, non-toxic, and chemically inert gas. It is contained inside a small, sealed bulb deep inside the HID assembly. The actual light that we see is produced when electricity jumps across a 3/16^th-inch gap between two electrodes inside the sealed xenon bulb assembly. HID headlights are up to three times brighter than the more common halogen headlights. HID lamps are becoming more popular; however, BMW reports that their first xenon lights appeared over 20 years ago on several 1993 model-year BMWs.

So, what is meant when responders are told that if they touch a HID headlight at a crash scene, they will be shocked or (worse yet) electrocuted? What is all this hype about? One instructor even warns that if your hands (or other body parts) come in contact with the “rogue high-voltage arc” inside a HID headlight, you will “likely be thrown from the vehicle.”

This University of Extrication articles looks at what hazards exist for responders and what we should do when working with a vehicle at a crash scene that has HID headlights. First, let’s review the facts and address the urban legends and myths that surround this automotive technology.

Truth about HID headlights

It is true that HID headlights operate on high voltage; however, the amperage is low. An electric ballast, similar to that found in a fluorescent lamp, converts the car's 12 volts DC (direct current) to up to 25,000 volts AC (alternating current) when the headlight is first turned on. This high voltage creates an arc that jumps across the small gap inside the electrodes of the sealed lamp unit. This energizes the xenon gas, causing the gas to produce the bright light. Once the arc is formed and the headlight warms up, the voltage drops to approximately 80 volts AC.

To understand the risk of electricity at crash scenes, we must first accept the fact that a person contacting an energized source of high voltage can be injured or killed. With that understanding, let’s use a brief “Reality Check” hazard checklist to consider the safety concerns surrounding high-intensity-discharge headlights at crash scenes:

1) The 12-volt DC and the high-voltage AC current is only present when the headlight circuit is turned on and the vehicle’s electrical system is intact.

2) If the headlights are turned OFF or the vehicle’s 12-volt electrical system is shut down, no DC or AC current is present within the HID headlight.

3) The high-voltage AC, when present within the HID unit when it is turned ON, is present inside an approximately three-inch-long, sealed glass bulb that is about the size of a person’s little finger.

4) This bulb is typically at the rear portion of the headlight assembly, deep inside the headlight housing, and is not readily accessible.

5) To properly focus the light produced by the xenon gas, HID headlights use a thick glass lens. This lens is directly in front of the tip of the tubular xenon bulb and prevents direct contact with the xenon bulb from the front of the vehicle.

6) HID headlights utilize an outer cover of a plastic material at the very front of the headlight. This protective layer forms the outer shape of the headlight when it is mounted in the vehicle.

So, how would a rescuer make contact with and be injured or killed by the energized, high-voltage source present inside a HID headlight? What chain of events has to take place to allow this to happen? It would have to essentially be the “perfect storm” of events;

The vehicle’s electrical system would have to be completely functional after the collision.
The HID headlight switch and headlight electrical circuit would have to be intact after the crash
The HID headlight would have to be still illuminated; headlight ON.
The outer protective cover of the headlight unit would have to be broken away almost completely; large enough for a rescuer’s hand to be placed inside the headlight housing assembly itself
The thick, glass lens that focuses the headlight’s beam and its mounting bracket inside the HID unit would have to be displaced or torn off sufficiently enough that the small, xenon bulb would be accessible.
The glass cover of the sealed bulb would have to be broken away but the two thin electrodes would have to still be intact and gapped properly.
The rescuer would have to have a bare hand; no glove on, in order to fit into this small space
The rescuer would have to stick their hand directly into the broken but still illuminated HID headlight far enough that a finger touches the end of the electrodes while it is energized.

After all this, yes, a person could be shocked enough to cause injury or death. But, in reality, what is the likelihood of this actually happening? If the headlight is OFF or if the vehicle’s 12-volt electrical system is shut down, there will be no hazard.

Study the construction of a typical HID unit and decide for yourself how hazardous you feel that HID units really are. By understanding how HID headlights are designed and function, rescuers can develop safety protocols for working with a vehicle at a crash scene that has HID headlights and the degree of risk can be put into proper perspective along with all the other hazards and risks that can be present at a crash scene.