Unearthing the complex hazard of Electric Arc

A poll of hsmsearch.com readers revealed that a third
believed there was a lack of awareness of electric arc
flash burn in their workplace. Mike Frain and Elaina
Harvey discuss how to approach the management of
this deadly, but poorly understood risk

On the 10th October 2008,
electrical engineer, Paul
Ridings, 39, was engulfed by a
fireball at Lafarge Cement UK Plc in
Essex. He was investigating a fault with
an energy meter when he inadvertently
disturbed a loose connection and
exposed a strand of wire leading to an
electrical explosion. His clothes caught
fire and he sustained burns to his face,
neck, chest, arms and hands. He
received emergency treatment and
spent 19 days in hospital. Since the
incident he has undergone numerous
skin grafts and operations to remove
scar tissue. An investigation by the
Health and Safety Executive (HSE)
found the company failed to ensure
electrical systems were maintained in
such a way as to protect workers. The
company admitted breaching sections
2(1) and 3(1) of the Health and Safety at
Work etc. Act 1974, was fined £130,000
and ordered to pay costs of £29,742.

Unfortunately, electrical flashover or arc
flash is one of the most deadly and least
understood hazards of electricity and is
prevalent in most industries. Each year
around 1,000 electrical accidents at work
are reported and as many as 25 people die
from their injuries. It is widely recognised
the higher the voltage of an electrical
power system, the greater the risk for
people working on or near energised
conductors and equipment. However, arc
flash can actually be worse and more
common at lower voltages and can cause
devastating, severe burn injury and even
death.

What is an electric arc flash?
An arc flash is usually caused by
inadvertent contact between an
energised conductor such as a bus bar or
wire with another conductor or an
earthed surface. When this occurs, the
resulting short circuit current will melt
the conductors, ionise the air and create a
conducting plasma fireball with
temperatures in the core of the arc that
can reach upwards of 20,000 degrees
centigrade. Severe injury and even death
can not only occur to persons working on
the electrical equipment but also to
people located nearby.

Arc flash injury can include external
burns to the skin, internal burns from
inhaling hot gasses and vaporised metal,
hearing damage, eye damage such as
blindness from the ultraviolet light of the
flash as well as many other devastating
injuries. Depending on the severity of the
arc flash, an explosive force known as an
arc blast may also occur which can result
in pressures of over 100 kiloPascal (kPa),
launching debris as shrapnel at speeds up
to 300 metres per second (m/s).

Survivors of such injuries may require
extensive treatment and rehabilitation and
the cost of these injuries can be extreme,
physically, emotionally and financially.

Whilst legislation requires businesses to
perform risk assessments for all work
activities, electric arc risk is often
overlooked because most people are
unsure how to assess and manage this
hazard effectively.

How to manage the hazard
The arc flash hazard needs to be
determined by risk assessment out of
which, the decision to work live or dead
and the required precautions will be
derived. But the risk assessment should
provide more information than this and it
is advisable to adopt the step by step
approach of Predict, Prevent, Protect and
Publish that is recommended in the
DuPont Arc-Guide:
Predict – the severity of the thermal
effect of an arc flash by the amount of
“incident energy” that a victim,
standing at a given distance away from
the arc, could receive.

Prevent – design out, eliminate or
remove the hazard at its source.

Protect – where the risk cannot be
controlled by prevention or where
there is a residual risk of injury then it
may be necessary to consider personal
protective equipment (PPE) to prevent
injury to the worker.

Publish – communicate and document
results of site arc flash to those who are
at risk.

In Summary
The DuPont Arc-Guide has been
developed in conjunction with
independent experts, to help companies
better assess the arc flash hazards (with
the use of simple calculators) and provide
them with the knowledge on how to both
reduce the severity and consequences of
an arc flash.

To find out more visit
www.arcguide.dupont.com or contact
Linda Cubrilo, support coordinator on
the number below.

Mike Frain is an electrical consultant
for Electrical Safety UK and Elaina
Harvey is an account manager for
DuPont Nomex