User's Manual

7 Fluke Corporation Concerned about arc-flash and electric shock?
What is appropriate PPE?
Clearly, the potential injurious effects of an
arc flash can be reduced by using a fire flame
resistant (FR) suit of a suitable calorie rating
to reduce the indecent energy on the body to
an extent that the burns suffered are not life
threatening.
While safety is the paramount concern, it is
important to select PPE appropriate for the task.
It might seem a good idea to insist on category
4 PPE for all live work, perhaps to avoid a time-
consuming arc flash hazard analysis, and this
may outwardly appear to be a ‘safe’ policy for
personnel. However, the use of restrictive or
excessive PPE can also be hazardous: an over-
heating worker struggling with poor visibility
and restricted movement is more likely to have
an accident. More accidents, more downtime.
In addition, there are scenarios where HRC
may not be enough arc-flash protection. The
HRC does not account for arc-blast.
NFPA 70E provides several tables listing the
PPE appropriate for work within the flash pro-
tection boundary: clothing and equipment such
as gloves, hats or hoods.
In addition to the HRC classification, PPE is
often described by the arc thermal performance
value (APTV). This corresponds to the capability
of the garment to withstand a particular inci-
dent energy (in cal/cm²).
As we have already discussed, the flash
protection boundary defines the distance where
an arc flash would produce incident energy of
1.2cal/cm²: a level at which 2nd degree burns
could occur. This corresponds to risk category
0. In practice, a worker will need to approach
the electrical system much closer than the flash
protection boundary. It is therefore important
to calculate the likely incident energy for the
working position and select PPE accordingly.
Most garments are tested and rated for incident
radiation at a distance of either 18 inches or
24 inches. This roughly corresponds with the
position of the head and chest when work-
ing directly on equipment. Of course, during
an arc flash incident, the hands and arms may
be much closer to the arc fault source and may
need protective equipment with a considerably
higher rating.
While NFPA 70E and IEEE 1584 cover the
PPE requirements for arc flash protection, there
are also other considerations and standards to
include in any safety appraisal. Workers may
require eye protection, insulating gloves, ear
and hearing protection, head impact protection
and reinforced footwear.
Heeding the warning signs
Equipment such as “Switchboards, panel-
boards, industrial control panels, meter socket
enclosures, and motor control centers in other
than dwelling occupancies, which are likely
to require examination, adjustment, servicing,
or maintenance while energized, shall be field
marked to warn qualified persons of potential
electric arc flash hazards. The marking shall be
located so as to be clearly visible to qualified
persons before examination, adjustment, servic-
ing, or maintenance of the equipment.”
Although the basic requirement is for a sign
warning of the arc flash hazard (see Figure 6) it
is more helpful for engineers if the sign includes
other useful information such as:
•
Operational voltage
•
Fault current
•
Flash hazard boundary
•
Incident energy at the normal working dis-
tance for the arc fault hazard.
•
If this information is not present on the
warning sign, it should be documented and
accessible to all relevant personnel.
Figure 5. Examples of PPE for arc flash protection.
Copyright image courtesy of Salisbury by Honeywell