Page 323 - Offshore Electrical Engineering Manual

310 CHAPTER 4 Hazardous Area Installation

Table 5.4.3 Relationships Between Different Methods of Assessing Safety
Levels

Level of Countable ATEX Normal Zone of
Protection Faults Category IEC EPL Use
ia 2 1 0 0
ib 1 2 1 1
ic 0 3 2 2

LEVEL OF PROTECTION ‘IA’
Intrinsically safe circuits in electrical apparatus of category ‘ia’ must not be capable
of causing an ignition during normal operation when two faults occur. The different
levels of protection and their interrelationships are given in Table 5.4.3.

1. in normal operation and with the application of those non-countable faults
which give the most onerous condition;
2. in normal operation and with the application of one countable fault plus those
non-countable faults which give the most onerous condition;
3. in normal operation and with the application of two countable faults plus those
non-countable faults which give the most onerous condition.

LEVEL OF PROTECTION ‘IB’
Intrinsically safe circuits in electrical apparatus of level of protection ‘ib’ shall not be
capable of causing ignition in each of the following circumstances:

1. in normal operation and with the application of those non-countable faults
which give the most onerous condition;
2. in normal operation and with the application of one countable fault plus the appli-
cation of those non-countable faults which give the most onerous condition.

LEVEL OF PROTECTION ‘IC’
Intrinsically safe circuits in electrical apparatus of level of protection ‘ic’ shall not
be capable of causing ignition in normal operation. Where distances are critical for
safety, they shall meet the requirements of IEC 60079-11.
(Note: A countable fault is a fault which occurs in parts of electrical appara-
tus conforming to the constructional requirements of IEC 60079-11). The manu-
facturer is required to issue a certificate of conformity as typically shown in
Fig. 5.4.2.