Construction Blasting zones. A friend of mine who is aware of my SDMB connection asked me to pose this multipart question.
1.) Why do they advise you to turn off cell phones and two-way radios?
2.) Do they reasonably expect the born-with-a-cell-phone-growing-from-my-head types to comply?
3.) Why don’t the cell towers in the area produce a similar interference as to what a cell phone might cause?
I think we can assume that stray electomagnetic signals may close some of the switches or make the electronics think they are closed. I would hope that people would turn off their phones if asked. If the cell phone is nearby, it is likely that the signal irradiating you from the phone is much stronger that the one from the tower. I suspect that they do not position these consoles right under a cell tower, but even then, the received signal from the phone on your hip will be stronger.
Because under the right circumstances the RF from the cell phone could trick one of the elctronically triggered detonators into making a big kaboom.
Yep. They also try to make sure that all of their electronics are shielded so that idiots who won’t turn the phones off because they don’t realize they can blow themselves up won’t actually blow themselves up. But you never know for certain that they did everything right. But hey, what’s the worst that can happen, besides like a few dozen deaths and horrible maimings?
Because they are farther away. The signal drops off as the square of the distance from the transmitter. Both the cell phone and the tower are transmitters. The tower is in fact a bigger transmitter and puts out a lot more power, but just happens to be located farther away from the blast site.
I don’t think so. AFAIK, detonating systems are designed to be as robust and failsafe as possible. This means heavy mechanical switches and simple, insensitive circuitry. And blasting caps themselves require a fair amount of energy to be triggered, so RF-induced voltages in the wires probably won’t set them off accidentally–certainly not from a cell phone. Two-way radios, maybe. But only in the very close vicinity of the blasting. See here:
I read once (sorry don’t have a cite) that one of the reasons is that the mobile phone network does not handle phones that are physically traveling at almost 600 mph very well. If enough people were using them this way all the time, it could cause problems for the network because phones would be switching towers too rapidly for the way it was designed. Don’t know all of the details.
Sorry, completely wrong topic. I was so used to people asking about use on planes that I skimmed past the OP way too fast.
What if the wires are a quarter-wave or half-wave (or multiple) at the frequency being used by the transmitter? What if the blasting cap is at a voltage or current node on the wire? It may be one of those situations where the conditions have to be just right for something bad to happen. It may also be why det cord is so popular today for initiating explosives.
Paranoia!
Thanks, folks, for the replies so far. engineer_comp_geek - I would’ve expected that some blasting zones are occasionally close enough to towers that the tower’s signal would still be stronger than the cellphones…
See http://www.dir.ca.gov/Title8/8554.html for a table that lists the hazardous distances for a wide variety of radio transmitters at various frequencies and power levels. For example, you don’t want to be within 2,800 feet of an AM broadcast station operating at 50kW. Mobile HF transmitters, such as those used by amateur radio operators, have a hazard radius of close to 1,000 feet at full power.
What if one has to blast within the radius of a Cell Tower? Do you just get the company to shut it off?