posted 08-06-2004 02:01 AM                      

quote:

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Mishaps: Exploding panels... Misc. tools damaged by "dead" circuits

Shocks: 480v, 277v lighting (hurts a LOT);
DC hit from a rectifier... 115v, 400 cycle aircraft power

Highest voltage with direct contact: 12,000 volts.

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Doesn't sound like booth work has been your strong suit. The idea is to avoid getting bitten!

posted 08-06-2004 07:27 AM                       

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Three primary factors affect the severity of the shock a person receives when he or she is a part of an electrical circuit:
Amount of current flowing through the body (measured in amperes).
Path of the current through the body.
Length of time the body is in the circuit.
Other factors that may affect the severity of the shock are:
The voltage of the current.
The presence of moisture in the environment.
The phase of the heart cycle when the shock occurs.
The general health of the person prior to the shock.
Effects can range from a barely perceptible tingle to severe burns and immediate cardiac arrest. Although it is not known the exact injuries that result from any given amperage, the following table demonstrates this general relationship for a 60-cycle, hand-to-foot shock of one second's duration:

Current level
(in milliamperes) Probable effect on human body
1 mA Perception level. Slight tingling sensation. Still dangerous under certain conditions.
5 mA Slight shock felt; not painful but disturbing. Average individual can let go. However, strong involuntary reactions to shocks in this range may lead to injuries.
6-30 mA Painful shock, muscular control is lost. This is called the freezing current or "let-go" range.
50-150 mA Extreme pain, respiratory arrest, severe muscular contractions. Individual cannot let go. Death is possible.
1000-4300 mA Ventricular fibrillation (the rhythmic pumping action of the heart ceases.) Muscular contraction and nerve damage occur. Death is most likely.
10,000 mA Cardiac arrest, severe burns and probable death.

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quote:

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The severity and effects of an electrical shock depend on a number of factors, such as the pathway through the body, the amount of current, the length of time of the exposure, and whether the skin is wet or dry. Water is a great conductor of electricity, allowing current to flow more easily in wet conditions and through wet skin. The effect of the shock may range from a slight tingle to severe burns to cardiac arrest. The chart below shows the general relationship between the degree of injury and amount of current for a 60-cycle hand-to-foot path of one second's duration of shock. While reading this chart, keep in mind that most electrical circuits can provide, under normal conditions, up to 20,000 milliamperes of current flow


Current Reaction
1 Milliampere Perception level
5 Milliamperes Slight shock felt; not painful but disturbing
6-30 Milliamperes Painful shock; "let-go" range
50-150 Milliamperes Extreme pain, respiratory arrest, severe muscular contraction
1000-4,300 Milliamperes Ventricular fibrillation
10,000+ Milliamperes Cardiac arrest, severe burns and probable death

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quote:

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ABSTRACT: Since clinical signs of underlying injury, especially skin appearance, may fail to indicate the severity of the actual injury from electrical current exposure, you must maintain a high index of suspicion for life-threatening injury. The major cause of death in patients with electrical injuries is cardiac dysrhythmia. In the emergency department, use cardiac monitoring for all patients with electrical injuries and, regardless of external signs of exposure, obtain an ECG. Emergent cardiac catheterization should be performed for a patient who has clinical signs of a myocardial infarction. Laboratory tests for patients with electrical burns should include creatine kinase levels, complete blood cell count, electrolyte levels, renal function tests, and urinalysis. Technetium 99m scans have been found to be very sensitive in identifying injured muscle. The goals of surgical management are to remove devitalized tissue, prevent infectious complications, and preserve as much tissue as possible. (J Crit Illnes s. 2002;17(3):94-100)

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posted 08-06-2004 11:05 AM                    

quote: Bobby Henderson

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For instance, the third rail in the New York City subway system runs at 600 volts. But I don't know the level of amps in that rail.

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Bobby,

I don't know how much current goes through the third rail, either. But there is one thing I can tell you for sure...

There's enough to push a train!

Two of my worst electrical nightmares in the booth come from some idiot trying to replace diodes and getting them all mixed up. In both cases, the person literally put the new diodes in a pile and picked them randomly as they were installed. No attention was paid to whether they were "forward" or "reverse" diodes. In both cases, it led to a total meltdown of the recitfier.

In the CFS rectifier, the capacitors overheated and blew their guts all over the inside of the lamphouse and all of the wires fried themselves. Virtually the only things left intact were the heat sink/frame of the rectifier and the transformer. I had to strip out almost every other part and replace it with new. This includes the terminal blocks and the contactor. It was obvious that this rectifier had been abused this way before. Those CFS rectifiers may have their faults but they can take a lot of abuse before they shit the bed. This one had too much abuse and just died. There were several loose connections and overheated parts that were running on their last legs. When the brainstrust who put in the diodes turned the projector on after "fixing" it, the thing just went into "cascade failure" mode and melted down one piece at a time. I spent about 10 hours on a Saturday fixing that one.

After that, my boss gave me a portable Strong rectifier to keep on hand in case of a similar problem in another theater. The idea was simple: Just gut the old rectifier out of the lamphouse and connect the new one in its place, temporarily, until the replacement can be ordered.

It wasn't long after until some idiot did the same thing in a different theater. This time, on a Christie lamphouse. I don't know HOW the guy did it but he caught the thing on fire. I got the phone call from a frantic booth manager who didn't know what to do. I just told him to shut the machine down and shut off all the breakers to that machine. If the fire isn't too bad, it SHOULD burn itself out in a minute or two. I said, "If the fire doesn't go out in a minute or if it starts to spread outside the projector pull the fire alarm, evacuate the building and let the fire department take it from there.

Fortunately, it didn't get that far. The fire went out almost immediately after the machine was shut down. The whole main terminal board was fried beyond recognition but the rest of the rectifier was in good shape. I installed the portable rectifier and put in the order for replacement parts. (Why do these things always happen on a Saturday night?! )

So a short time after that I got another call from the same theater who told me that the replacement rectifier had blown up! No! It wasn't the classic failure that the Strongs do by going up in smoke, etc. Somebody had fiddled with the thing like I specifically told them NOT to do. I told them, "Don't even TOUCH it!" Appearelty some goof ball touched it and shorted something out because the report that I got was that there was a loud popping noise and a big spark of electricity which "threw him against the wall."

I can guarantee that kid was tinkering when he was specifically told not to! I set things up in a specific way so as to avoid such problems but when I got there to fix it... AGAIN... things were in a different place than where I had left them.

What burns my ass is not that people make mistakes and mess things up but they continue to do these things even AFTER they have been specifically told HOW or how NOT to do things!

I still maintain that both of these incidents border on willful neglect and destruction of the equipment!

posted 08-06-2004 12:32 PM                    

quote:

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Doesn't sound like booth work has been your strong suit. The idea is to avoid getting bitten!

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posted 08-06-2004 03:10 PM                      

quote: Tony Bandiera Jr

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Tim: Quite the contrary. That was pretty much the full list of over 30 years working with electricity and 20-some in the booth.

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Yeah, I know, I's just teasin' ya. Sounds like we've got similar backgrounds.