Determining tasks which require Arc Flash PPE

[mull982]

We recently had an Arc Flash study completed here at our facility and I am in the process of taking the reults from this study and implementing them in the field in order to determine what PPE levels are required for a given task on a given piece of equipment. One of the challenges I am coming across is determining what kind of tasks require Arc Flash PPE.

From NFPA 70E article 100 the FPN 1 under the definition for Arc Flash Hazard states the following:

"An arc flash hazard may exist when energized electrical conductors or circuit parts are exposed or when they are within equipment in a guarded or enclosed condition, provided a person in interacting with the equipment in such a manner that could cause an electric arc. Under normal operating conditions, enclosed energized equipment that has been properly installed and maintained is not likely to pose an arc flash hazard."

Reading this I am trying to apply it to the following conditions and wanted to hear others opinions.

4.16kV switchgear

When troubleshooting or taking measurements in the control cubilce of the switchgear is it necessary to wear required necessary Arc Flash PPE. I would think yes since you are interacting with the system.

When racking in or closing a breaker, contactor, or switch, I would think that this would be considered interacting with the equipment and therefore would require the necessary Arc Flash PPE.

When reading meters etc.. even though you may be in the Arc Flash boundary you are not interfacing with the equipment and therfore no PPE would be required.

480V MCC

When opening a bucket (bucket breaker on or off) to work inside the bucket or take measurments do you need then necessary required Arc Flash PPE? I would think that in this case since there are live circuit conductors exposed then the answer would be yes? Even if you were working inside the bucket to change a small 120V control fuse?

When racking in a 480V bucket even though you are not exposed to live circuit conductors you are still interacting with the system and therefore need to wear the required PPE.

When operating the handle of a 480V circuit breaker with the door closed do you need to wear the required Arc Flash PPE? I would think this would be a case where you are interacting with the equipment.

I'd appreciate anyones comments or guidance on my questins related to which tasks need to follow the required PPE as defined in an Arc Flash report.

 

[kevin]

The answers to your questions can be found in NFPA 70E, 2009 Edition, Table 130.7(C)(9).
The Table tells, for various tasks performed on energized equipment: the hazard/risk category for selecting PPE, whether or not rubber insulating gloves are required, and whether or not insulated and insulating hand tools are required.

 

[mull982]

The answers to your questions can be found in NFPA 70E, 2009 Edition, Table 130.7(C)(9).
The Table tells, for various tasks performed on energized equipment: the hazard/risk category for selecting PPE, whether or not rubber insulating gloves are required, and whether or not insulated and insulating hand tools are required.

Yes but this table only gives PPE values for tasks based on an assumed fault level and device clearing time as indicated at the end of the table.

The avaliable fault current and device clearing times that I am dealing with are higher than published in this table.

 

[charlie b]

You named six tasks, and stated your opinion that only the third (reading a meter) does not require PPE. I agree.

Think of it this way: Start by presuming that, unbeknownst to anyone, the last time any work was done on the equipment someone inadvertently left a tool inside the enclosure. Anything you do that might jar the tool loose and cause it to fall onto an energized component is a task that requires PPE. Even simply opening the door to allow you access to replace a fuse could be enough to jar something loose inside. How much PPE you need at any panel is a function of the results of the arc flash study. So I think you are on the right track.

 

[mull982]

Think of it this way: Start by presuming that, unbeknownst to anyone, the last time any work was done on the equipment someone inadvertently left a tool inside the enclosure. Anything you do that might jar the tool loose and cause it to fall onto an energized component is a task that requires PPE. Even simply opening the door to allow you access to replace a fuse could be enough to jar something loose inside. How much PPE you need at any panel is a function of the results of the arc flash study. So I think you are on the right track.

This is a good way of thinking of the tasks being performed. So from what you said I basically gather that every task other than reading meters on outside panels requires the Arc Flash PPE as dictated by the results of the Arc Flash Study.

 

[petersonra]

You named six tasks, and stated your opinion that only the third (reading a meter) does not require PPE. I agree.

By reading the meter are you referring to looking at a meter that is hard wired in place? or putting the meter leads on some energized and exposed point inside the equipment?

I am pretty much unwilling to do anything around switch gear because I am not real familiar with it, so I just don't go near it. I do not even like walking by it, although some places almost force you to do so by where they locate things.

I am generally unconcerned about arc flash in a 120V control panel.

These days I avoid doing any manual labor at all, so I don't fiddle around in MCCs very much either anymore. Except when they are in our shop. I doubt our little 30KVA 208/480V xfmr can produce much of an arc.

 

[billsnuff]

it's all about the lables

it's all about the lables

You should have been provided labels for your equipment. The label should give you the correct gear to wear and the HRC. Ignore the task charts, use the labels.

First task is to work deenergized or use the electrically safe work permit in the annex, if deenergizing is infeasable.

check definitntion in 70E

 

[RoberteFuhr]

I also recommend that you not use the task tables as they have a very narrow range of applicability. The tables assume the device operating times. The time that the protective device operates has a huge impact on the arc flash energies. The task tables are to be used if you have nothing else (no other AF calculations or study) available.

 

[jghrist]

I think that there has to be some determination of what tasks pose an arc flash hazard, even if an incident energy analysis was made and the 130.7(C)(9) task table do not apply. Let's say you have a calculated IE of 5 cal/cm? for a 480V MCC, based on IEEE 1584. The calculations are based on direct exposure to an arc. Would you require Cat 2* PPE to operate a motor starter with the doors closed?

What if you were Dudley Do-Right and Snidely Whiplash had tied Nell to a log in a sawmill? Would you take the time to put on your 8 cal coveralls and replace your Canadian Mountie hat with a hard hat and face shield before shutting down the saw?

What would you think about this criteria?

NFA 70E Article 100 definition of Arc Flash Hazard, FPN No. 2 says

See Table 130.7(C)(9) for examples of activities that could pose an arc flash hazard.

If the HRC in the task tables is 0, then an arc flash is unlikely and HRC 0 can be used for that task (like starter operation with doors closed on a 480V MCC), even if an IE analysis was made and the task tables do not strictly apply.

 

[mull982]

I think that there has to be some determination of what tasks pose an arc flash hazard, even if an incident energy analysis was made and the 130.7(C)(9) task table do not apply. Let's say you have a calculated IE of 5 cal/cm? for a 480V MCC, based on IEEE 1584. The calculations are based on direct exposure to an arc. Would you require Cat 2* PPE to operate a motor starter with the doors closed?

What if you were Dudley Do-Right and Snidely Whiplash had tied Nell to a log in a sawmill? Would you take the time to put on your 8 cal coveralls and replace your Canadian Mountie hat with a hard hat and face shield before shutting down the saw?

What would you think about this criteria?

NFA 70E Article 100 definition of Arc Flash Hazard, FPN No. 2 says

If the HRC in the task tables is 0, then an arc flash is unlikely and HRC 0 can be used for that task (like starter operation with doors closed on a 480V MCC), even if an IE analysis was made and the task tables do not strictly apply.

This is kind of where my challenge has set in. I know the table outlines certain tasks however as we discussed the PPE values listed in this table may be somehwhat lower due to fault level and operating times.

So using your example yes the tables do show an HRC of 0 for operating a starter with the doors closed. However this value is based of the IE level avaliable from their given fault current and operating time conditions. In my case with higher fault currents and longer device operating times the IE levels are most likely higher and therefore the HRC for a given task will be higher. So for a task such as this that could be an HRC of zero from their table may now be higher based on the numbers from my study. This is my main challenge of determining weather or not certain tasks can just use the same HRC as the tables regardless of the study results or if all the tasks in the table need to be adjusted to the HRC's listed in the study results.

I am tending to lead towards the opinions of others above which state that for most of the tasks referenced in this table they involve interacting with the system and should therefore require the level of PPE as dictated in the study.

 

[kingpb]

Reading meters, if you are within the arc flash zone, and the gear is energized, then you will need PPE.

Suppose you are standing in front of the gear reading the meter and the breaker operates, whether by remote operator action or trip? This is the most likely time that an arc flash will occur, so how can you say no PPE would be required.

 

[jim dungar]

So using your example yes the tables do show an HRC of 0 for operating a starter with the doors closed. However this value is based of the IE level avaliable from their given fault current and operating time conditions.

This is not true.

The Hazard/Risk Categories are not based on any incident energy value at all. They are based on the probability of an amount of injury, during an incident, more than anything else.

Yes, there is a possible incident energy that could be calculated using the maximum values listed in the footnotes (i.e. 65kA for .03sec). But, then there would be no purpose in listing multiple HRCs for each type of equipment, for example all equipment subject to footnote #2 would have the same Ei and therefore would require the same PPE.

 

[mayanees]

Study results only...

Study results only...

Zog must be away from his machine, so I'll chime in on this one in his stead...
You can't mix PPE tables and study results, nor would you want to. The Study produced labels for the gear. Any time the gear is interacted with, abide by the PPE requirements of the label. Interact is Operate, Maintain, Demolish or Construct.
John M

 

[mull982]

Yes, there is a possible incident energy that could be calculated using the maximum values listed in the footnotes (i.e. 65kA for .03sec). But, then there would be no purpose in listing multiple HRCs for each type of equipment, for example all equipment subject to footnote #2 would have the same Ei and therefore would require the same PPE.

Yes but it sounds like others are saying that this is indeed the case. That based on the IE level and category determined from the Arc Flash study all tasks for a piece of equipment would have the same EI and same PPE requirements no matter what the task.

 

[jim dungar]

That based on the IE level and category determined from the Arc Flash study all tasks for a piece of equipment would have the same EI and same PPE requirements no matter what the task.

Absolutely, when you have an incident energy value, it is applicable to all tasks "provided a person is interacting with the equipment in such a manner that could cause an electric arc" (from NPFA70E-2009 FPN #1 to definition of Arc Flash).

My point is the task tables are not based on any calculated incident energy. They are based on a 'gut feel' that the odds of getting severally injured vary solely with the task.

 

[zog]

I agree with Jim. Sorry been at Power Gen all week with 19,000 of my closest friends.