Assignment for Hazardous areas Document Preview: Advanced Diploma of Industrial Automation (DIA12) Assignment for Module Twelve HAZARDOUS AREAS Rev 6 Your Name:...

Solution to objective questions
1 D
2 B
3 B
4 D
5 C
6 A
7 A
8 A
9 C
10 D
11 D
12 A
13 D
14 C
15 D
16 B
17 C
18 C
19 A
20 C
21 B
22 C
23 D
24 C
25 D
26 A
27 C
28 C
29 D
30 C
Question 31
Certain types of protection (Ex d, Ex i, Ex p, etc.) are only permitted for
installation in particular Zones. Explain in simple terms why this is the
case?
The type of installation in particular zones depends on the requirement
and safety of the system. For instance in zone 0 maximum protection is
equired and hence even the contacts have to be protected where as
such requirement is not there in zone 2. Obviously zone 0 equipment is
more complex and hence costlier. So the type of protection depends on
two factors : safety requirement and the economical cost associated.
Question 32
Explain why it is important to ensure that Earthing and Bonding
associated with a Hazardous Area should be of high integirity?
Earthing is important because in case of any fault it will minimize the
damage by providing alternative path to the high fault cu
ent.
Bonding is required to ensure that potentials between conducting
parts (i.e. the metal casements of motors and transformers) to
prevent dangerous voltages appearing between the frames of
electrical equipment.
Hence both are very important and so should be of high integrity.
Question 33
Ex i circuits require the inclusion of a certified interface between the
Safe and the Hazardou areas. Ba
iers or Isolators may be used but
what is the major difference in the way they achieve protection?
In the field of explosion protection, intrinsic safety (Ex-i) is an important
protection type. In the event of a failure, energy limitation in the circuit
in potentially explosive areas plays a decisive role in ensuring
protection. Both the ba
iers and the isolators are interfaces between
the sensor or the actuator in the Ex-i area and the controller. The
energy limitation can be achieved with help of a circuit design with
Zener diodes and resistors.
Ba
iers, also known as "safety ba
iers", must be connected to the
equipotential bonding system of a system along the shortest possible
oute. This means that the circuit cannot be grounded at another point
in the Ex-i- circuit in order to prevent voltage equilization cu
ents.


Colloquially, the term "isolator" is also used for an intrinsically safe
isolation amplifier and a measuring transducer, which as opposed to
the ba
ier, have pre-connected electrical isolation in addition to the
energy limiting circuit. This isolation is also known as buffer stage or
electrical isolator. Equipotential bonding is not necessary in an Ex-i
isolator and the connected field devices may be grounded during the
operation.
One of the major difference is that the ba
iers need a explicit
grounding point where as a grounding point is not required in the
isolators.





Q34
An Ex i certified Shunt Diode Safety Ba
ier comprises the following
safety components:-
40.1 What is the purpose of the series resistor?
The role of series resistor is to limit the cu
ent
40.2 What is the purpose of the zener diode?
It fixes the clamp voltage
40.3 What is the purpose of the fuse?
Fuse it protects the circuit from large cu
ent.
Q35
If test equipment is to be taken into and operated in a Hazardous Area,
in general terms, what requirements must be met to assure that it is
acceptably safe and cannot provide a source of ignition?
Insulated testing of the equipment should be done. This should be
undertaken with normal High Voltage test equipment at the pre-
commissioning (‘detailed’) inspection stage. Immediately afterwards
it is recommended that low voltage...