Gentlemen, I am new to this site and joined to get some information about a job at my complex. (I am an operations Shift Leader)
This job involves the following activities:
1- The armored power cables are inside an underground concrete trench, filled with sweet sand and covered with red bricks.This is buried 1.6 meters.
2- A new roadway is to be built to cross over the underground trench. The project proposed that the following work be performed while the power cables are still hot and in-service: 2-A: The trench be excavated, red bricks be removed, sweet sand to be removed, exposing the armored power cables. 2-B: The construction crew will then manually arrange the power cables in order, place split pipe covers around each cable, build concrete forms in the trench, then poor concrete to make the trench into a duct bank which the road expansion can be built over.
Well, when these people came to my unit for an excavation permit, and a confined space entry permit to work on these live armored power cables, I convened a meeting of the concerned parties (part of the permitting process) and scheduled a Job Safety Analysis to discuss hazards and required mitigation steps for the identified hazards.
My problem is that I have never been involved with this type of work in my many years in chemical plants and need a crash course on the hazards and what type of Personal Protective Equipment (PPE) and precautions should be in-place prior to human contact with these cables.
So far I have pushed things along the lines of choosing between a regular confined space entry and a breathing air required confined space entry with an IDLH atmosphere.
I am requiring an explanation of why portable power stations can not be supplied and the breakers isolated per our Lock Tag and Try policy.
If I am pushed into letting these men manipulate these hot armored cables, I need to know if this is normal work practice and how this can be done safely.
Any information on this type of activity will be greatly appreciated!
1) How is a 5-ft. deep trench, open it's entire length, considered a 'confined space?'
Company policy calls for any excavation deeper than one meter and or belt depth to be a confined space entry due to collapse concerns, if a person has to lay down in the trench to work and his head or shoulders are exposed to collapse dangers even shallower trenches are confined space permit required.
2) What sort of voltage and current are the cables using?
This is one of the items I sent the electrician off to find out, I suspect 220V and 480V but it could be higher, the electrical department have not gotten back to me yet.
3) How do you plan to get the sand out from around the cables?
The worker will take the "Sweet" sand out by hand tools, this sand is a pure white, sugar looking sand.
4) What condition do you expectthe sand to be in? Wet, with mud mixed in? Clean and dry?
The conditions should be warm and dry but very dusty
5) What is 'sweet' sand? Is it like beach sand, or perhaps like decomposed granite (cannot be compressed)?
It is a very clean fine grained sand, looks like it has been sifted clean of any debris. It is quite compressible.
[i][/i]Our local weekend is coming to an end tomorrow so I might find out more tomorrow. [i][/i
#205925 - 04/27/1204:27 PMRe: Working with live underground armored power cables
Thank you all for your responses, please keep them coming. I think I have succeeded in kicking this permit further up the food chain where it belongs. The company is very safety conscious and I will see to it that people with the expertise will be involved with any further discussions.
The simple answer is to cut the power, install a proper LTT in the Breaker room (MCC) and supply any temporary power for vital equipment.
#205929 - 04/27/1207:51 PMRe: Working with live underground armored power cables
Can live cables be manipulated while energised? Yes. Should they? No
It sounds like the original installation they were careful to ensure the cables were laid correctly and without damage but what condition are the jackets now? is the internal armour still in tact? Is it damaged? how do you re-arange cables that are now arranged? ie are they currently stqacked and placed in sets now? if the ends are connected then the layout and arrangements of the cables are set already and you'd have to disconnect at least 1 end to change the order of things.
Use the vactor truck which can remove the sand dry or wet. set up saddles across the trench and lash the cables in their configuration to the cross members. It will prevent sagging from pulling out the wires from their terminations which is your greatest risk of failure. pull a live wire out of its connector could result in major repairs. ropes and cross beams can go a long way in preserving the layout as well as can act as cribbing for the concrete. You can also clean and pour in 10 foot stages clean out the sand and brick over 10 feet form for concrete and pour. move the next 10 feet down and repeat. An open trench is not a confined space normally but it is an excavation and may require a geotech or ditch forms to protect the workers.
#206415 - 06/29/1207:38 PMRe: Working with live underground armored power cables