Yokogawa EJA118 - Manual (Page 65)

EX-A03E 2
INSTALLATION AND OPERATING PRECAUTIONS FOR JIS INTRINSICALLY SAFE EQUIPMENT
— when up to two countable faults are applied and, in
addition,
— when non-countable faults produce an onerous
condition.
(5) Apparatus of category “ib”: Intrinsically safe electrical
apparatus and associated apparatus which are incapable
of causing ignition of a given explosive gas or vapour,
with the appropriate safety factors such as:
— when up to one countable fault is applied and, in
addition,
— when non-countable faults produce an onerous
condition.
(6) Safety rating: A rating to be designated to intrinsically
safe apparatus as well as associated apparatus and is the
maximum rating allowable for maintaining intrinsic
safety of concerned intrinsically safe circuits.
4. Caution on Combining Intrinsi-
cally Safe Apparatus and
Safety Barriers
(1) A combination of certified intrinsically safe apparatus
and safety barriers needs to satisfy combination
requirements. If intrinsically safe apparatus specify
safety barriers for combination, safety barriers other than
specified cannot be used (see Note 1 for more details).
(2) Certified intrinsically safe systems specify specific safety
barriers in combination with intrinsically safe apparatus.
So safety barriers other than specified cannot be used
(see Note 2 for more details).
(3) Other than limitations of combining intrinsically safe
apparatus and safety barriers as given in (1) and (2)
above, two or more pieces of apparatus certified under
different standards cannot be combined with each other
(see Note 3 for more details). In addition, bear in mind
that classifications of explosion protection such as “IIA,”
“IIB” and “IIC” and category “ia” and “ib” limit a
combination of intrinsically safe apparatus and safety
barriers.
For more details, see the “Type Certificate Guide for
Explosion-Protected Constructionfor Electrical
Machinery and Equipment,” issued by the Japanese
Ministry of Labour, the Research Institute of Industrial
Safety.
Note 1: Testing Apparatus
Intrinsically safe apparatus and safety barriers are assessed
individually to ensure that their safety requirements are
satisfied. Tested and certified intrinsically safe apparatus and
safety barriers incorporate individual certification numbers.
A combination of intrinsically safe apparatus and safety
barriers involves the following two limitations:
(1) A safety barrier which meets the combination require-
ments by referring to its safety rating and combination
parameters shall be selected.
(2) For pressure transmitters, pH transmitters, temperature
detectors and the like, safety barriers that can be
combined are already specified. Other safety barriers
cannot be used.
Note 2: Testing Intrinsically Safe System
An assembly (as a system) in which intrinsically safe
apparatus and safety barriers are combined is assessed to
ensure that its safety requirements are satisfied. A tested and
certified system incorporates a certification number
(intrinsically safe apparatus and safety barriers have the same
certification number).
Note 3: Impossible Combinations of Apparatus Certified Under
Different Standards
Intrinsically safe apparatus certified under technical criteria
and safety barriers certified under the “Recommended
Practice for Explosion-Protected Electrical Installations in
General Industries” (1979) and vice versa cannot be
combined even if their combination requirements are
satisfied.
5. Installation of Intrinsically Safe
Apparatus and Safety Barriers
(1) Classification of installation location
Intrinsically safe apparatus may be installed, depending upon
applicable gases, in a hazardous area in Zone 0, 1 or 2 (Note
4 below), where the specified gases are present. However,
note that apparatus certified under Technical Criteria, in
category “ib” shall be installed only in Zone 1 or 2. Safety
barriers (associated apparatus) that are combined with these
intrinsically safe apparatus shall be installed only in a non-
hazardous area. In cases where safety barriers are installed in
a hazardous area, they shall be enclosed, for example, in a
flameproof enclosure.
Note 4: Hazardous areas are classified in zones based upon the
frequency of the appearance and the duration of an explosive
gas atmosphere as follows:
Zone 0: An area in which an explosive gas atmosphere is
present continuously or is present for long periods.
Zone 1: An area in which an explosive gas atmosphere is
likely to occur in normal operation.
Zone 2: An area in which an explosive gas atmosphere is not
likely to occur in normal operation and if it does
occur it will exist for a short period only.
(2) Ambient temperature limits for intrinsically
safe apparatus
Intrinsically safe apparatus shall be installed in a location
where the ambient temperature ranges from –20
°
to +40
°
C
(for those certified under Technical Criteria) or –10
°
to
+40
°
C (for those certified under the “Recommended Practice
for Explosion-Protected Electrical Installations in General
Industries” (1979). However, some field-mounted