Chemical Engineering July 2015 - 50

Environmental Manager
Things You Need to Know Before Using an
Explosion-Protection Technique
Understanding the different classification methods is necessary to better select the
explosion-protection techniques that will be used
Class I, Division 2
(from 5 ft to 10 ft radius)
Class I, Division 1
(5 ft around vent)
Zone 2
Vent
Outdoors
10 ft (3m)
Gasoline
storage
tank
without
floating
roof
Zone 0
10 ft (3m)
Circular dike
around tank
Gasoline
storage
tank
without
floating
roof
Zone 1
Vent
Class 1, division 2
FIGURE 1. Shown here is a typical example of a Class I hazardous area utilizing
division methods of area classification
Robert Schosker
Pepperl+Fuchs
E
xplosion protection is essential
for many companies, and
those companies have decision
makers. But before any
decisions can be made, there are
some important factors one must
consider. These factors include what
is most efficient and economical, as
well as knowing the basics of explosion
protection; so the decision makers
are headed in the right direction.
We will highlight many of the different
" things to know, " but first, let's step
back in time and take a look at the
background of explosion protection.
Backdrop
After World War II, the increased
use of petroleum and its derivatives
brought the construction of a great
number of plants for extraction, refining
and transformation of the chemical
substances needed for technological
and industrial development.
The treatment of dangerous sub50
FIGURE
2. The example hazardous area shown in Figure 1 is here classified according
to the zones
stances, where there exists the
risk of explosion or fire that can be
caused by an electrical spark or hot
surface, requires specifically defined
instrumentation located in a hazardous
location. It also requires that
the interfacing signals coming from
a hazardous location are unable to
create the necessary conditions to
ignite and propagate an explosion.
This risk of explosion or fire has
been the limiting factor when using
electrical instrumentation because
energy levels were such that the
energy limitation to the hazardous
location was difficult, if not impossible,
to obtain. For this reason, those
parts of the process that were considered
risky were controlled with
pneumatic instrumentation.
Moving forward
Now let's move forward 70 years,
where almost everything you can
think of can be found at the touch of a
finger. From pneumatics to quad core
processors, information gathering
has definitely changed, but the same
principles for working or gathering
information out of a hazardous area
remain the same. It's just that today
we have multiple options. In order to
exercise those options, we must first
determine if the danger of an explosion
exists and how severe it may be.
What is a hazardous area?
Hazardous areas are most frequently
found in places where there is a possibility
of an emission of flammable
gas or dust. A hazardous area can
occur in normal operation, in the
event of a fault, or due to wear and
tear of seals or other components.
Now the risk of an ignition of an
air/gas mixture in this hazardous
area depends on the probability of
the simultaneous presence of the
following two conditions:
* Formation of flammable or explosive
vapors, liquids or gases, or
combustible dusts or fibers with
atmosphere or accumulation of
explosive or flammable material
* Presence of an energy source (electrical
spark, arc or surface temperChemiCal
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Chemical Engineering July 2015

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