Hazardous areas and safety
Conclusion
• For new installations requiring long cable runs, classifying the
area as zone 2 offers significant benefits.
• For upgrading existing plants where the new loop approval fails,
there are actually two options:
o Re-classify the hazardous area as zone 2, use Exic andmake
use of the higher Co value. If this is possible, this is a simpler
option.
o If it is not possible to reclassify, there is an alternative
due to be defined in the new ARP0108 [3] due
out shortly ie there is the availability of a ‘risk
assessment’ for these loops (reference in
A.10).
If a change to loop apparatus results in incompatible
safety parameters in accordance with the certification
standard, the ATL may consider the use of risk assess-
ment methods and a concession may be issued.’
In both cases, Exic offers some flexibility and allows
for upgrades of old control systems improving safety.
Regarding equipment for Zone 2 - in Europe, the ATEX
directive allows for Cat 3 self certification (eg ExnA non-
arcing). Due to the low risk of ignition and high skills pro-
ficiency (suppliers and end-users), this is acceptable. Most
ExnL ATEX certified product was also Cat 3 self-certified.
However, with changing to Exic, this is now covered
by the third party Exi certification (with minimal extra
work or cost), making it an accepted practice in South
Africa.
References
[1] IEC/SANS 60079-11: 2012. Electrical apparatus for
explosive gas atmospheres, Part 11: Equipment
protection by Intrinsic safety 'i'.
[2] IEC/SANS60079-25. 2010. Explosive atmospheres Part
25: Intrinsically safe electrical systems.
[3] ARP 0108: 2007. Regulatory requirements for explo-
sion-protected apparatus. To be read in conjunction
with SANS 10108.
T
ake note
A
bout the author
Gary Friend completed his BSc Electrical Engineering
at the University of Witwatersrand in 1990. He worked
for Temperature Controls at various stages between
1986 and 1992. In1992 he worked as a design engineer
for LTH Electronics in the United Kingdom, designing
process control instrumentation for water quality moni-
toring. Gary joined MTL in November 1995 where he
program managed the MTL4500 galvanic isolators development. In 2006,
he returned to South Africa and he joined Extech Safety Systems. In 1995
he registered with MIET and is a registered Chartered Engineer (UK). He
is registered as a Professional Engineer (SA) with ECSA. Gary sits on the
Johannesburg branch of SAIMC committee, Ex-steering committee and
IS sub-committee of SA Flameproof Association and is Chairman of the
Fieldbus Foundation Southern African Marketing Committee. Enquiries:
Tel. 011 791 6000 or email
A
bbreviations
ARP - Address Resolution Protocol
ATEX - Explosive Atmospheres (ATmosphere EXplosibles)
ATL - Accredited Test Laboratory
CENLEC - European Committee for Electrotechnical Standardisation (Comité
Européen de Normalisation Électrotechnique)
DCS - Distributed Control System
Exnl - Energy Limiting
IEC - International Electrotechnical Commission
IS - Instrinsically Safe
SANS - South African National Standards
• ExnL (energy limiting) was a technique used for zone
2 which was effectively intrinsically safe in normal
operation.
• ExnL (energy limiting) has been reassigned as Exic.
• With the new standards, it is clear that Exic loops can
be run in the same trunking as other Exic loops.
