It is currently Thu Feb 22, 2018 3:37 am



Post new topic Reply to topic
Author Message
ekstra   ara
 Post subject: Flash Hazard boundry
PostPosted: Fri Jul 18, 2014 12:16 pm 
Offline

Joined: Wed May 29, 2013 12:30 am
Posts: 4
Location: Pune, India.
i found that, after running the arc flash study, the calculated flash hazard boundry like 89mm or 112mm somewhat..Where the Restricted boundry is 305mm. Is it right?. What is the correct arc flash boundry to be mark?


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Flash Hazard boundry
PostPosted: Fri Jul 18, 2014 1:12 pm 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
They are different boundaries for different reasons. The definitions are in NFPA 70E. Basically:

1. Arc Flash Hazard Boundary - approach limit where at that distance one would receive a second degree burn. Typically this is where the arc flash is 1.2 cal/cm^2

2. Restricted Approach Boundary - approach limit from an exposed energized conductor or part where there is an increased risk of shock.

So for your arc flash hazard, you would use the arc flash hazard boundary.

It doesn't seem like it is a lot of incident energy for the boundary. What is the IE and voltage level?


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Flash Hazard boundry
PostPosted: Fri Jul 18, 2014 10:21 pm 
Offline

Joined: Wed May 29, 2013 12:30 am
Posts: 4
Location: Pune, India.
Thanks for your reply.
IE is 0.07 cal/cm^2 at 415v.

I am confused at, what should be the Arc Flash protection boundary to be mark. Is there any necessary for this flash hazard boundary?


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Flash Hazard boundry
PostPosted: Sat Jul 19, 2014 4:17 am 
Offline
Plasma Level
User avatar

Joined: Wed May 07, 2008 5:00 pm
Posts: 711
Location: Rutland, VT
Not sure where you are located but in the USA, if one is subject to NFPA 70E, then Article 130.5(C) has the labeling requirements. A label is required if it is electrical equipment like switchboards, panelboards, motor control centers etc that are likely to require examination, adjustment, servicing or maintenance while energized.

The label needs:
1. At least one of the following:
*incident energy and corresponding working distance
*minimum arc rating of clothing
*required level of PPE
*Highest risk category
2. Nominal system voltage
3. Arc flash boundary
The method of calculating and data to support the information on the label shall be documented.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Flash Hazard boundry
PostPosted: Sat Jul 19, 2014 7:01 am 
Offline
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 1878
Location: North Carolina
The arc flash hazard at the working distance is less than 1.2 cal/cm^2. The working distance is based on an ergonomic estimate of the most vulnerable parts of a workers body to burn injuries (face and chest), since 2nd degree or greater burn injuries in those areas are most likely to lead to a ftality whereas even total loss of limbs is rarely fatal. As of right now the standards are based on minimizing exposure, and minimizing likelihood of a fatality if exposure occurs.

Thus in your case, the arc flash boundary is somewhat meaningless as it is less than the working distance. Thus no special PPE other than nonmelting clothing is necessary. Working distance varies from one piece of equipment to another. The arc flash boundary does not exist when the likelihood of causing an arc is very low. It is assumed that "spontaneous arcing" and similar events happen so rarely that when equipment is operating normally (properly installed, properly maintained, properly engineered), that arc flash hazard does not warrant PPE. This would include activities like just walking by. In these tasks, ignore the boundary. These tasks are also site specific. So for instance the act of opening a door on equipment with conductive dust surrounding it such as near metalworking equipment might be an arc flash hazard but the same activity in a clean and dry environment might be very different. It also changes depending on the specific task. For instance meter reading and similar noncontact activities where there are no exposed energized conductors or no conductive items or body parts are within the limited approach boundary are unlikely to cause an arc flash.

The restricted approach boundary is a totally different concept for a totally different hazard, shock. This is the point where shock protection methods (tools, techniques, PPE) must be used, irrespective of the arc flash boundary. It is zero when there are no exposed, energized conductors.

The limited approach boundary is the distance to keep unescorted unqualified workers away from exposed, energized equipment.

Finally, there is no definition for this, but the "combined" boundary (greater of arc flash and limited approach boundaries) is the distance to maintain for unqualified workers when both hazards are present.

Also the general concept of the arc flash boundary is a sphere (open air) or hemisphere (in a panel). But it is not unlimited. I have one area with a calculated arc flash boundary over 1000 m. So realistically it extends to the concrete block walls and for some distance in front of the exterior doors. Further although the standard uses a table of exponents which take into account things like a hemispherical pattern, the concept falls down when the arc flash extends beyond the equipment. It is realistically nowhere near that distance, no matter what the math says.


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Flash Hazard boundry
PostPosted: Sun Jul 20, 2014 10:03 am 
Offline

Joined: Wed May 29, 2013 12:30 am
Posts: 4
Location: Pune, India.
OK. Thanks for your reply. i am sure on that, there is no requirement for drawing the boundary at such a less distance. But is there any specific standard for that?


Top
 Profile Send private message  
Reply with quote  
 Post subject: Re: Flash Hazard boundry
PostPosted: Mon Jul 21, 2014 6:19 am 
Offline
User avatar

Joined: Tue Jul 07, 2009 1:20 pm
Posts: 13
Location: Lima, OH
The whole point of these labels with their corresponding boundaries is to be able to give the information necessary for the properly trained worker to quickly assess the level of hazard so he/she can make a proper determination of the necessary safe electrical procedures and PPE. Although it might seem that it would not be necessary to have such an insignificant boundary distance, to leave it off would leave the worker without crucial information and he/she would have to go to the tables to make the estimates in a more laborious fashion. So yes, I would say that even labels with arc flash boundaries less than the working distance should most definitely be in place.


Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 7 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
© 2017 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883