Efficient Plant April 2022 - 32

column | safety insights
Check Your
Arc-Flash
Boundaries
Vince Plank, CSP
Safety Management Group
T
WO COMMON CAUSES of
electrical fatalities in the workplace
are electrocution and arc flash/
blast. To minimize injuries and fatalities,
OSHA implemented electrical safety
standards more than 40 years ago. In 2007,
those rules were updated to provide consistency
between OSHA (osha.org) and many
state and local building codes, most of
which adopted the updated National Fire
Protection Association (NFPA, nfpa.org)
and National Electrical Code provisions.
OSHA's General Industry and Construction
standards regulate work " on and
near " energized equipment and who is
authorized to perform this work. The NFPA
70E " Standard for Electrical Safety in the
Workplace " provides guidance for employers
and employees on safe work practices, risk
assessment, and other controls. While both
require de-energized work when feasible,
there are times when de-energization is not
possible. According to NFPA 70E, work on
energized systems by qualified persons is
only allowed when the employer can show
that de-energizing will introduce additional
hazards or increased risk, such as interruption
of life-support equipment.
Have you measured/checked your arcflash
shock-protection boundaries lately?
Vince Plank is a Safety Advisor at Safety
Management Group, Indianapolis, IN
(safetymanagementgroup.com). He is a
Certified Safety Professional with almost
20 years of occupational safety and
health experience in general industry and
construction. Contact him at VincePlank@
safetymanagementgroup.com.
32 | EFFICIENTPLANTMAG.COM
DEFINING ARC FLASH
An arc flash is the light and heat produced
as part of an arc fault, a type of electrical
explosion or discharge that results from
a low-impedance connection through
air to ground or another voltage phase
in an electrical system. The blast is the
supersonic shockwave produced when
the uncontrolled arc vaporizes the metal
conductors. Both are part of the same arc
fault and are often referred to as simply an
arc flash. From a hazard standpoint they
are often treated separately.
What causes the arc fault that leads to an
arc flash/blast? The most common cause is
spark discharge that results from accidental
contact with or dropping tools near energized
equipment. Other causes include dust
and impurities on insulating surfaces, corrosion
of equipment that creates impurities on
insulators, condensation or water-vapor drip
that causes tracking on insulator surfaces,
and failure of insulating materials.
Arc flash is incident energy, measured as
calories/cm2 at the working distance. The 70E
Standard states that it is the owner's or host
employer's responsibility to perform an arcflash
risk assessment/analysis. The assessment
identifies arc-flash hazards, estimates
the likelihood of occurrence and potential
severity of injury or damage to health, and
determines protective measures, including
boundaries and personal protective equipment.
Often
an engineering group is contracted
to perform an incident-energy analysis.
This method uses the available energy or
fault current, the working distance, and the
clearing times of the electrical distribution
system over-current protective devices. The
threshold, or arc-flash boundary, required
to provide protection is 1.2 cal./cm2
. This
amount of energy will cause a second-degree
burn and likely require medical treatment,
making it an OSHA recordable incident.
There are two shock-protection boundaries,
limited and restricted. These are fixed
and based on voltage and can be found in
70E table 130.4 (E)(a) for AC systems, and
130.4 (E)(b) for DC systems. This assessment
leads to a report and electrical-equipment
labels for switchgears, panelboards,
motor-control centers, and other equipment.
The 70E Standard requires an assessment
update when changes are made to the
electrical distribution and/or at least every
five years. EP
APRIL 2022
http://www.osha.org http://www.nfpa.org http://www.safetymanagementgroup.com http://www.EFFICIENTPLANTMAG.COM

Efficient Plant April 2022

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