Electrical hazards to tree workers around bucket trucks.

[Treedbear]

I just read in the news about a tree worker who got electrocuted when the bucket truck that was being used to trim trees touched a power line. The worker was standing on the ground and touched the truck and got electrocuted. I've heard about this happening before and thought they had ways to avoid it by using non-conductive bucket lifts. However wouldn't it be pretty easy to have an alarm set up that detected whenever the truck had a charge on it? I'd assume a simple wire or chain dragging on the ground with a detector similar to a ground fault isolator on a home electrical outlet would work. My co-worker says no. I need some backup on this.

 

[thebeave]

I just read in the news about a tree worker who got electrocuted when the bucket truck that was being used to trim trees touched a power line. The worker was standing on the ground and touched the truck and got electrocuted. I've heard about this happening before and thought they had ways to avoid it by using non-conductive bucket lifts. However wouldn't it be pretty easy to have an alarm set up that detected whenever the truck had a charge on it? I'd assume a simple wire or chain dragging on the ground with a detector similar to a ground fault isolator on a home electrical outlet would work. My co-worker says no. I need some backup on this.

You not only have to detect the electrification of the truck (which is the easy part), but you need to somehow quickly kill the power (within milliseconds, ideally) to keep him from getting electrocuted. How would you do that? GFCIs do both quickly, so they are effective.

 

[Sarpedon]

You would need a lot of ground fault interruptors on the power lines itself, not the truck. How could such an interruptor tell the difference between a short like you describe and merely increased usage? The lines carry enough power that the amount needed to kill someone is trivial in comparison, unlike your bathroom outlet, which can easily tell the difference between the load of your electric shaver and a potentially fatal short.

Grounding the truck seems to be more promising, but such measures are notorious for getting skipped by rushed and poorly educated workers.

You could build the arm and bucket out of fiberglass or some other insulating material, but these are bulkier, more brittle and weaker than metal, as well as more expensive.

 

[Treedbear]

Thanks for the advice. I agree that if the worker is already touching the truck when it contacts the power line an alarm is useless. But this seems to be a case where the truck was already live before the workman touched it. I only brought up the GFI because it's very sensitive to power drain. But there's probably other ways to measure charge, such as a high impedance probe attached to a wire or chain dragging on the ground that would trigger a warning alarm.

According to the report:

The boom on the truck reportedly came in contact with the power lines, which run down the driveway, energizing the truck, police said.

The victim, who was working on the ground, then went to open the door of the truck and was shocked,

ETA - My friend at work claimed you'd need a hard ground connection to detect the charge. I told him he doesn't know what he's talking about in this case. I pointed out that the worker wasn't making a hard ground, although I don't know if the ground he was standing on was wet. Anyway, a simple chain dragging on the ground would likely have at least as good contact. My friend countered that a person is composed of water and so makes a better connection, which began to sound absurd.

 

[fromderinside]

Safety processes normally require defining worst case scenarios. Man, truck, cherry picker, wire, seems one that should be explored from all angles on intersection of man with electricity. Wherever man intersects any subset that includes wire need be accounted. I prefer a solution that disables electricity when it may come in contact with man. Insulating man seems to be correct solution. Men working around electrical transmission requires men be insulated. The whole man. If there is any risk of wire down or equivalent I believe this is the normal requirement.

 

[Treedbear]

Tree workers are an unruly lot.

 

[fast]

I just read in the news about a tree worker who got electrocuted when the bucket truck that was being used to trim trees touched a power line. The worker was standing on the ground and touched the truck and got electrocuted. I've heard about this happening before and thought they had ways to avoid it by using non-conductive bucket lifts. However wouldn't it be pretty easy to have an alarm set up that detected whenever the truck had a charge on it? I'd assume a simple wire or chain dragging on the ground with a detector similar to a ground fault isolator on a home electrical outlet would work. My co-worker says no. I need some backup on this.

You not only have to detect the electrification of the truck (which is the easy part), but you need to somehow quickly kill the power (within milliseconds, ideally) to keep him from getting electrocuted. How would you do that? GFCIs do both quickly, so they are effective.

How about a separate secondary back up device designed specifically to only emit an audible alarm alerting those in the vicinity of the dangers—in the event the primary, better, and superior GFCI isn’t operating?

 

[steve_bank]

The bucket may be non conductive but the lift part is not. It would be easy to measure the voltage from chassis to earth and flash a horn and light if a voltage is detected. Electrical workers wear insulating gloves and shoes.

Tree trimmers could wear rubber boots around the truck.

If the truck itself is grounded and it contacts a power line the current would be huge, a short circuit. I Imagine there could be explosive results.

 

[Sarpedon]

yeah, THAT would trip the breaker at the substation.

 

[Treedbear]

The bucket may be non conductive but the lift part is not. It would be easy to measure the voltage from chassis to earth and flash a horn and light if a voltage is detected. Electrical workers wear insulating gloves and shoes.

Tree trimmers could wear rubber boots around the truck.

If the truck itself is grounded and it contacts a power line the current would be huge, a short circuit. I Imagine there could be explosive results.

From what I've witnessed in my own yard there's very little supervision of what's going on around the truck itself. And they might have training for the equipment operators but there's often several lower paid buggy luggers cleaning up brush and moving cut limbs. Also the homeowner might be lurking about unsupervised. But I wouldn't ground the truck. That'd probably cause a major arcing before the circuit breaker blew, as you said. I just want a high impedance probe like on a DVM that doesn't need to pass a lot of current. In fact the higher impedance the better since the ground connection itself might be rather weak if it's on dry grass or asphalt. It would probably be very inexpensive to do and wouldn't require any expertise to put in use. When the bucket goes up the monitor turns on and the alarm beeps to let everyone know it's working.

 

[steve_bank]

A proximity detector could be designed to sound an alarm when the lift section gets close to a line. You can buy cheap power line detectors to find wires in walls. Sold in hardware store.

Training probably consists of 'do not let the truck touch the wires'.

Also the legs extended for stability would make an earth connection.

It is easy to make a voltage meter with an adjustable threshold detector. Maybe $100 in parts including an enclosure.

Industrial grade insulating rubber boots would work. They are catalog items.

 

[skepticalbip]

An old engineering expression - It isn't difficult to make something fool proof but a damned fool will always find a way to overcome it.

I think a lot more concern is being shown than this incident deserves. The fact that this incident made the news is because such accidents are so rare. They are so rare because there are already safety procedures in place to avoid them. Life itself is risky and reasonable precautions should be taken to minimize them but risks can never be completely eliminated. The risk of the entire crew dying in a traffic accident on the way to the job was likely much greater than the risk of electrocution once on the job. In this case, the best solution would be not to have careless people operate the bucket... a damned fool that doesn't watch for power lines will defeat almost any safety device developed.

 

[steve_bank]

In the news media I think it is more 'if it bleeds it leads'.

 

[Treedbear]

An old engineering expression - It isn't difficult to make something fool proof but a damned fool will always find a way to overcome it.

I think a lot more concern is being shown than this incident deserves. The fact that this incident made the news is because such accidents are so rare. They are so rare because there are already safety procedures in place to avoid them. Life itself is risky and reasonable precautions should be taken to minimize them but risks can never be completely eliminated. The risk of the entire crew dying in a traffic accident on the way to the job was likely much greater than the risk of electrocution once on the job. In this case, the best solution would be not to have careless people operate the bucket... a damned fool that doesn't watch for power lines will defeat almost any safety device developed.

If it cost $100 and required no maintenanace and it might save a life it would be worth it. But apparently your sensibility is the one that prevails.

 

[Sarpedon]

That's not the problem. The problem is that it would cost 1000 dollars for every truck, and the guys won't use it.

 

[Gun Nut]

In the news media I think it is more 'if it bleeds it leads'.

I'm surprised that there haven't been torch carrying protests calling for the resignation of everyone... because that is how we "fix" inevitable, rare accidents... ban, resign, shame....

 

[steve_bank]

A solution would be a rubber sheath over the arm that expands and contracts with the arm.

 

[Sarpedon]

Or rubber boots.

 

[Treedbear]

A proximity detector could be designed to sound an alarm when the lift section gets close to a line. You can buy cheap power line detectors to find wires in walls. Sold in hardware store.

Training probably consists of 'do not let the truck touch the wires'.

Also the legs extended for stability would make an earth connection.

It is easy to make a voltage meter with an adjustable threshold detector. Maybe $100 in parts including an enclosure.

Industrial grade insulating rubber boots would work. They are catalog items.

Thanks steve. All I was really interested in was whether the thing would work conceptually. Not so much all the alternatives solutions.

 

[steve_bank]

A proximity detector could be designed to sound an alarm when the lift section gets close to a line. You can buy cheap power line detectors to find wires in walls. Sold in hardware store.

Training probably consists of 'do not let the truck touch the wires'.

Also the legs extended for stability would make an earth connection.

It is easy to make a voltage meter with an adjustable threshold detector. Maybe $100 in parts including an enclosure.

Industrial grade insulating rubber boots would work. They are catalog items.

Thanks steve. All I was really interested in was whether the thing would work conceptually. Not so much all the alternatives solutions.

I know. Kind of like past lunch time what if conversation.

The environmentalists would ban power lines. The conservatives would ban trees as a solution...