Conference Papers | 2005 Victorian Conference Papers
AREAS FOR WATER & WASTEWATER FACILITIES
Director - Electrical & Mechanical,
Maunsell Australia Pty Ltd
identification and management of hazard areas is a key
issue, particularly in the operation of water and wastewater
plants where the presence of gases such as methane and
Hydrogen Sulphide can generate potentially hazardous
areas. Hazardous areas are those defined in the wiring
rules as areas of potential explosion risk due to the
presence of flammable gas or vapour. This paper presents
information relevant to the classification of hazardous
areas based on current Australian Standards. The correct
application and limitations of current standards are
outlined and the use of alternative standards such as
NFPA 820 are also discussed.
relationship of current hazardous area classification
and electrical installation requirements in hazardous
areas are introduced in the context of minimising the
likelihood of explosions. Finally, new directions in
standards are introduced including current development
work within the IEC, (International Electrotechnical
Commission), to include alternative approaches to hazardous
area classification based on risk assessment.
Hazard, Explosive, Gas, Wastewater, Electrical
are many hazardous areas associated with the water industry,
these include physical, biological and environmental.
This paper considers those 'hazardous areas' as defined
in Electrical Wiring Regulations as potentially explosive
atmospheres. Within the water industry such potential
is most commonly associated with the possible presence
of methane or hydrogen sulphide (H2S) gas. However,
there are other materials that may also give rise to
potentially explosive conditions.
Within the water industry potentially explosive atmospheres
are commonly associated with wastewater treatment plants
and underground sewer systems.
Australia has a well established standard (AS/NZS 2430.3),
which provides examples and guidance on considering
hazardous areas. While a useful guide, this standard
is by no means a complete solution. There are many situations
where there is a need or justification to depart from
the examples provided.
Australia has also recently adopted international standards
for hazardous areas (IEC 60079-10). While, in principle,
this standard has a similar intent to the previous Australian
standard (AS 2430.1), it is an over-ruling standard
to AS/NZS 2430.3 and provides for alternatives in approaching
The future is even more complex and as changes in international
standards flow on to Australia more variances in classification
will become acceptable. This paper briefly reviews current
standards related to classifying hazardous areas in
the water industry and looks at possible future changes.
2.1 Current Australian Standards
'umbrella' standard for classification of hazardous
areas is AS/NZS (IEC) 60079-10. This standard allows
for classification from first principles (assessment
and calculation), or, classification 'by example'.
AS/NZS 2430.3 'Classification of Hazardous Areas - by
Example' is the current Australian standard predominately
used for classifying hazardous areas as it is easy to
apply. Specific examples for the waste water industry
are found in AS/NZS 2430.3.6.
When considering classification by example there are
a number of critical points to be aware of. These include:
The classifications provided are EXAMPLES. They are
example classifications cover only selected situations.
Other situations may be relevant to hazardous area
classification and these need to be identified by
the site owner/operator and assessed separately.
not covered in AS/NZS 2430.3.6 should not be taken
as non hazardous.
examples are based on typical factors for such items
Plant conditions (assumed well maintained)
and operation to recognised standards.
in any of these items is justification for variance
from the example, for both increasing and decreasing
The use of other recognised codes such as NFPA (National
Fire Protection Association - USA) may be accepted.
do not consider issues such as CONSEQUENCE, TOXICITY
or oxygen depletion.
by the use of examples can, and occasionally should,
be overridden by 'classification by calculation'. This
approach is identified in AS/NZS (IEC) 60079-10.
The adoption of the IEC (International Electro-technical
Commission) standard is part of a long term policy by
Australia for international standardisation. The adoption
of IEC standards also means Australia will be bound
to accept future developments in the international arena.
In the USA, NFPA 820 is the reference standard for hazardous
area classification of waste water treatment facilities.
In recent years this standard has come to the attention
of some water authorities in Australia and has caused
some concern based on the premises applied and the large
number of situations identified as potentially hazardous.
NFPA 820 sets criteria for ventilation and makes many
assumptions on the likelihood of flammable gas release
that could rightfully be challenged and so should be
used with caution.
of classification items raised by NFPA 820 that are
not identified in AS/NZS 2430.3.6 include common features
and wet wells
ground pump stations.
at first glance it may seem unnecessary to classify
these items as hazardous the potential for gas to be
present, particularly under different ventilation conditions
should not be ignored off hand. One needs also to consider
operational reality and how overall risks are managed.
If personnel in a sewer system are required to carry
methane or H2S detectors does this not suggest a hazard
might exist? If a potential hazard exists then perhaps
the area should be classified as a hazardous area.
2.3 Current IEC Standards
Fifteen years ago Australia committed to a policy of
working towards the adoption of IEC standards related
to hazardous areas.
this point in time all of the equipment and classification
standards have been adopted and progression towards
the installation standards is well underway.
policy of adopting IEC standards is characterised as:
A very positive and successful decision for Australia
and worldwide standardisation
continued effort by Australians to influence IEC developments
to suit our needs and desires. (To date Australia
has been successful well beyond our global weight
in influencing IEC developments)
Australia to adopting new IEC standards 'warts and
current IEC standard (IEC 60079-10) has been adopted
in Australia embodies principles which are closely aligned
to the previous Australian standard, (AS 2430.1), has
been readily accepted.
current standard provides some basic calculations and
a few examples for classifications. However, it needs
to be clearly understood that:
The calculations provided are grossly oversimplified
and may lead to overly conservative results
calculations within the standard provide a basis for
assessment of ventilation - not assessment of gas
calculations, or modelling, are accepted
are not relevant to the wastewater industry.
short, AS/NZS (IEC) 60079-10 is only of use to the wastewater
industry in providing general principles and calculations
should use a model relevant to the situation.
Wastewater Treatment Plants
Irrespective of which standard is referenced there are
undeniable hazardous areas associated with wastewater
treatment plants, particularly where digesters and gas
recovery systems are involved. Having recognised the
obvious most engineers immediately refer to AS/NZS 2430.3.6
for the solution.
studies by Maunsell Australia, however, have shown that
there may be cause to vary the examples shown in AS/NZS
2430.3.6. This is particularly relevant where gas sources
are indoors and can include items such as:
in galleries and basements.
The relationship of the gas source and ventilation is
critical. For many plants hazardous areas may not be
an issue but cases have been encountered where even
with forced ventilation there is a high possibility
of gas accumulation.
Figure 1 shows an example of analysis where a gas leak
in a ventilated compressor room resulted in a hazardous
area despite forced ventilation.
Figure 1: Gas Accumulation
in a Ventilated Compressor Room
Figure 2 shows an example where a small gas release
in a gallery could result in significant layering of
gas, within flammable limits, near the ceiling. These
figures illustrate the sensitivity of indoor gas releases
to ventilation for achieving adequate dispersion.
2: Gas Accumulation in a Pipe Gallery with inadequate
Current Risk Approach
All current standards, worldwide, for the classification
of hazardous areas are based on probability factors
- what is the likelihood and likely area of a gas or
vapour release. The potential for electrical equipment
to act as a coincident ignition source is also considered
on probability. The likelihood of an explosion is then
considered to be as low as reasonably practical:
Likelihood of Explosion
Likelihood of Gas Presence x Likelihood of Ignition
ALARP event (As Low As Reasonably Practicable)
Electrical equipment installed in hazardous areas of
higher likelihood is designed to present a lower probability
of acting as an ignition source. This approach, current
terminology and requirements for electrical equipment
are typified in Table 1.
1: Current risk approach for hazardous areas
Under current standards the specifications for electrical
equipment operating in each hazardous area 'zone' are
tightly specified. However, despite the very strict
standards in place for possible ignition by electrical
sources standards are generally not applied for even
higher probability mechanical ignition sources.
Future IEC Standards
Development is well underway for the next edition of
IEC 60079-10 due in mid 2007.
This next edition of IEC 60079-10 will introduce an
option for significant change in the way hazardous area
classifications are considered. This change is driven
by consideration of 'true risk' as defined in AS 4360
and European council directives. These European council
directives are commonly known as the 'ATEX' directives
and require compliance with essential health and safety
principles for hazardous areas.
'True risk' is not solely based on probability and also
considers consequence. Typical risk principles are illustrated
in Table 2.
Table 2: Typical risk table
If hazardous area classifications are based on true
risk then there are a number options that could be considered.
These options include:
Installing high integrity explosion protected equipment
in any zone where there is potential for a fatality
from an explosion
the use of explosion protected equipment in any location
where gas may exist - no matter how improbable due
to the potential for injury
installing explosion protected equipment in a 'zone
2' area as there is no potential for personal injury.
(Or using 'zone 2' equipment in 'zone 1 areas.)
'zone 2' equipment in 'zone 1' where there are additional
safeguards to mitigate an explosion risk, e.g. additional
explosion suppression systems
scenarios represent possibilities that are both more
and less stringent than current practices. They highlight
the need for operators and asset managers to be aware
of the changes and consider what the new standards might
hold for them. These changes will also require more
consideration by managers in classifying areas in a
broader risk assessment context.
In order to select and apply equipment that is appropriate
to the risk, new identification systems are proposed
for the classifications and the relevant apparatus for
use in each classification. This new identification
system is illustrated in Table 3.
Table 3: Equipment safety and
the next edition of the IEC standards the categorisation
of hazardous areas and equipment will be introduced.
What will not be defined, however, is consequence. The
consequence criteria will need to be considered further
and agreement on standard, or uniformly accepted, consequence
criteria may be a future issue for industry and government
Finally the IEC is expanding the scope of activities
and standards to include other than electrical equipment
for hazardous areas. This then opens the way for the
specification and categorisation of explosion protection
for items such as motors, gearboxes, compressors and
other systems. These latest changes will reinforce the
need to consider all issues associated with flammable
gases in a broad risk management context.
already adopted the current IEC standard for the classification
of hazardous areas Australia is also committed to adopting
the future revision to this standard and is likely to
adopt future standards for non electrical equipment.
for hazardous areas are changing and broadening. Operators
and asset managers should be aware of the following
Hazardous areas in wastewater facilities are often
very sensitive to ventilation issues that are not
well defined in relevant standards.
Broad, hazard identification and risk assessment principles
should be followed when dealing with potentially explosive
atmospheres not just 'code compliance'.
examples covered in relevant standards may not be
appropriate or the only hazardous areas.
provided in standards are rarely relevant. Personnel
undertaking assessments need to understand the standards
and have access to other tools and information.
Adoption of IEC standards is undoubtedly a positive
policy for Australia. The changes proposed for hazardous
area classifications are the most significant in 50
years and should be embraced as being consistent with
broader risk principles. The changes will, however,
take time to resolve and put pressure on industry to
come to terms with a common understanding of risk.
author acknowledges the technical staff at Maunsell
Australia Pty Ltd for the input provided in modelling
complex gas dispersion and ventilation. Acknowledgment
is also provided for the experience gained particular
to the waste water industry via several studies completed
for SA Water.
AS/NZS (IEC) 60079-10; (2004); Electrical Apparatus
for Explosive Gas Atmospheres - Classification of Hazardous
AS/NZS 2430.3.7; (2004); Classification of Hazardous
Areas - Examples of Area Classification - Landfill Gas,
Sewerage Treatment and Pumping Plants.
AS/NZS 2381.1; (2005); Selection Installation and
Maintenance of Electrical Equipment for use in Potentially
Explosive Atmospheres - General Requirements.
NFPA 820; (1999); Fire Protection in Wastewater Treatment
and Collection Facilities.
Maunsell Australia Pty Ltd 2005
information contained in this document has been produced by
Maunsell Australia Pty Ltd solely for the WIOA for the purpose
of a presentation at the WIOA conference, September 2005.
Maunsell Australia Pty Ltd undertakes no duty to or accepts
any responsibility to any party who may rely upon this document.
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section or element of this document may be removed from this
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