User's Manual

5 Fluke Corporation Concerned about arc-flash and electric shock?
8. Determine incident energy. Calculate the
incident energy resulting from an arc fault at
the working distance.
9. Determine flash protection boundary. Use
the same calculations to estimate a ‘safe’
distance from the source of the arc hazard
beyond which PPE is not required. This paper
describes the Flash Protection Boundary in
more detail later.
Shock hazard analysis
As the name implies, the determination of the
shock hazard is an analysis designed to reduce
the risk of electrocution. NFPA 70 recommends
the identification of three boundaries to define
the safe working limits for personnel working in
an area with shock hazards. Each area is associ-
ated with a level of training and PPE.
NFPA 70E data (contained in Table 130.7(C)(2)
allows you to calculate the boundaries using a
formula based on the voltage of the equipment.
The limited approach boundary
This is the minimum permitted distance that
unqualified and unprotected personnel may
approach a live component. Before crossing the
limited approach boundary and entering the
limited space, a suitably qualified person must
use the appropriate PPE and be trained to per-
form the required work. An unqualified person
may enter the limited approach area if they are
under the supervision of a qualified person.
The restricted boundary
To cross the restricted boundary and access
the restricted space, personnel need to have
been trained in shock protection techniques, be
wearing the correct PPE and have a written and
approved plan for any work in the zone. The
plan must make it clear that the worker must
not enter the prohibited space or cross the pro-
hibited boundary either personally or by using
any equipment or tool.
Prohibited boundary
No worker should cross the prohibited boundary
and enter the prohibited area unless:
•
The responsible authority has carried out a
full risk assessment.
•
The work has been documented and it has
been fully established why it must be carried
it out on live equipment.
•
The qualified worker has been trained to
work on live electrical equipment.
•
The worker has been equipped with appro-
priate PPE. In terms of safety, any worker
crossing the boundary must be equipped and
protected as they would be for making direct
contact with the exposed live equipment.
Establishing these boundaries is an important
step in protecting staff from the dangers of
electrocution. It ensures that personnel use the
correct equipment and procedures when in the
proximity of live electrical equipment.
However, if the live equipment also poses an
arc flash hazard, it is important to establish a
‘safe’ distance for this eventuality: the arc flash
protection boundary.
The flash protection boundary
The arc flash protection boundary (FPB) is the
minimum ‘safe’ distance from energized equip-
ment that has a potential for an arc fault. It is
defined as the distance at which, in the event
of an arc flash, a worker would be exposed to a
thermal event with incident energy of 1.2 cal/
cm² for 0.1 second. With this exposure, a worker
may receive a 2nd degree burn to exposed skin.
If it is necessary for workers to cross the flash
protection boundary, and potentially be exposed
to higher incident energies from any arc flash,
they must be wearing appropriate PPE. For
example, at an incident energy greater than
1.2 cal/cm², clothing could ignite and bare skin
would sustain 2nd degree burns.
Figure 2. The shock hazard boundaries