strobe lights and explosives

[ruble3]

Not sure if this is the right forum- we use 12VDC strobe lights on vehicles , but also have electric detonators in use- someone heard throught the grapevine that the capacitors in strobe lights could cause detonation of blasting caps? I guess same theory as radio tramsmitters on construction sites- am trying to get info on the capacitor used from the manufacturer but no luck yet- Not sure what potential 'power' a capacitor in a strobe light may produce? (sorry the info is limited but it's hard to get it so far)

 

[candu6]

A capacitor stores a charge, like a battery. So, it you connected a charged capacitor to a blasting cap, then you can make it explode.
I think something may have been changed in the story when you heard it. Radio transmitters are banned from blasting caps because they may transmit a signal to a blasting circuit and cause an unplanned detonation. A capacitor, by itself, won't cause a blasting cap to explode unless it is connected to it.

 

[analogkid2digitalman]

Was pondering that the rapid discharge of the cap into the xenon strobe may cause a localized broadband EMI/RFI disturbance that may have the potential to detonate a nearby blasting cap.

Hands-on (actually hands-off preferably) testing could be a blast!

Wonder if there are any formal publications/codes/guidelines for transmitter and device restrictions available.

Wheels within wheels / In a spiral array
A pattern so grand / And complex
Time after time / We lose sight of the way
Our causes can't see / Their effects.

 

[BJC]

Call somebody at MSHA.
If it's a problem they should know about it.

 

[ruble3]

BJC; the issue was raised at a meeting that is a sub-group of MASHA - it is not known yet if there is indeed a hazard, partly I guess because of a lack of research- I'm not sure how the issue was first brought up or who might have recognized there may be a hazard- the explosives companies have been contacted but no replies yet - I think analogkids explanation seems reasonable-now we have to find hard data if there is any

 

[Comcokid]

Strobe lights consist of a capacitor charged through a high voltage source that is discharged through a transformer - the secondary of which is connected to the strobe bulb.

Analogkid's response points to the issue - what is the RF spectrum radiated from the strobe light? Another question would be how does the spectrum from one strobe light compare to that made by other manufacturers?

One could guess that the RF spectrum is not much different that that emitted from the ignitions system of a vehicle engine. But to be safe you would have to perform some RF emissions tests to determine the energy/spectrum present.

 

[jraef]

The problem is, who wants to drive the truck with a stobe flasher on it into a blasting zone to find out!

The way these things usually start is that probably someone did get killed or injured while doing so, and after the fact they could not find out why. So someone blamed it on the one piece of electronics that was there at the time, however unreasonable it might seem. The same was said about cell phones at gas stations, and it turned out to be bunk. The real culprit was found likely to be static discharge from exiting the car, but people were looking for something more complicated than that. Add to that the fact that it is cheaper to ban them than it is to test them and you have the basis for an "urban legend" that begins to affect policy. It's just easier to specify rotating beacons that to do enough testing to satisfy every possible future claimant AND THEIR LAWYERS!

"Venditori de oleum-vipera non vigere excordis populi"

 

[IRstuff]

Based on your description, the capacitor is only part of your problem:

discharged through a transformer - the secondary of which is connected to the strobe bulb

suggests that the voltage at the strobe is even higher and is pulsed, while the capacitor's voltage, while high is essentially a DC voltage.

The pulse transformer is also an RF emitter and as such will need to qualified for HERO - hazards of electromagnetic radiation to ordnance, which is covered by ADS-37A or MIL-STD-464

TTFN

 

[busbar]

 
Extreme long shots..

http://www.llnl.gov/es_and_h/hsm/doc_17.03/doc17-03.html

http://www.llnl.gov/es_and_h/esh-manual/volume2.html#s17

http://www.logicsouth.com/~lcoble/dir5/explosiv.txt

N.B., 24.09

One issue—for the given environment, are the detonators safer with leads shorted or unshorted?

 

[OperaHouse]

The flash circuit usually consists of a capacitor charged at a couple hundred volts. The flash is initiated by a pulse transformer of several thousand volts. Both of these could emit radiation because of the fast rise times. This could vary greatly from manufacturer. A fun experiment you could do is hold an AM radio tuned between stations close to it. You should be able to hear it flash. Then start walking away. The power will decrease with the cube of the distance. I doubt you will be able to hear anything after about 6'. You could always wrap the strobe light in metal screening.

I remember we made something that was going into a mine. We had to put resistors in series with all of the capacitors so that if the circuit ever shorted out, the current wasn't high enough to initiate an ignition spark.

 

[ruggedscot]

Strobe lights near explosives....

what you trying to do give someone the s..ts ?

Rugged

 

[OperaHouse]

Frankly, I think this is on the far end of reality. A lot of things generate EMI, like spark plugs in a vehicle or a switching speed control in a golf cart. The question is how much power is required to set off a device like a blasting cap. My understanding is these are thermal units. A length of wire connected to these could pick up radio frequencies and convert them to heat under certain conditions. That would likely take an order of magnitude of a watt. Tesla had dreams of transmitting energy through the air, it's not that easy. Two way radios turned off in a blasting ares. Sure, I know people with 1KW transmitters in their cars. That could induce enough power. Regulations have to be written so they are simple. You just can't put in qualifications that say this radio is ok and this one isn't and you can't control what is out there. I have a nice big construction strobe that is 30 years old. I'm sure that puts out more noise than one today with CE approval. If the detonators are that sensitive, they are what should be changed. I'm the first one to admit stuff happens. There are about five cases a year of cell phones exploding when people are talking on them. Now if we could just get those banned!

 

[ruble3]

I wasn't expecting this kind of resopnse but glad to see it-
Operahouse- changing the detonators is not an option
ruggedscot- depends..
While I was researching the use of RF equipment for underground I did come across this site- surprising what may set off an electric detonator& why

http://www.nclabor.com-osha-etta-indguide.ig11.pdf

Thanks for all the resopnses- I know one major company has removed them from service until more research done-rotating beacons I think are the answer in the meantime

 

[OperaHouse]

Well, that site was fun. Frankly, that is a lot closer than I would want to be to a 4,000 watt transmitter with explosives. As usual I learned something. My understanding was that the feed and return were always bundled together and that is highly imune to radiation pickup. Guess you want be to cheap when you just blow them up. Putting them in series and forming a big loop makes an ideal RF pickup. At the same time, putting them in series greatly increases the amount of energy needed and makes it safer. My comment was related to the prevelence of electronic devices and how hard it is to control the people that use them. A capacitor included in each of these detenators would make them highly imune to RF fields. From the charts I can't see how strobes would cause a problem. Using the CB 5W recommendations would be sufficient.

 

[Warpspeed]

I am with OperaHouse on this one.

What is really being asked is, can a strobe circuit couple enough energy into a nearby adjacent circuit to be dangerous ?

There are two issues, the energy available, and the efficiency of any coupling medium. The energy available in a vehicle strobe is not going to be very high, I do not know a figure, but my guess might be around 100 millijoules per flash, realistically about the same power as the discharge of an automotive ignition coil.

To couple energy into another circuit requires either magnetic, capacitive, or electromagnetic coupling. A vehicle strobe is a compact device without any large current carrying loops, or large flat exposed plates carrying rapidly changing high voltages.

A radio transmitter with antenna is DESIGNED to radiate RF energy and is going to be dangerous. Something of equal power with no functional antenna is going to be pretty harmless.

If you are worried, take a strobe around to the nearest EMC laboratory and get them to test it for various types of RF emissions. Get a written report, and ask their opinion.