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Risk assessment in a hazardous area?

Author : Jim Munro, Consultant and Chairman of IEC Committee TC31

16 May 2012

As a true blue Australian, I identify with one of our well-known poems by Dorothea Mackellar which starts:
I love a sunburnt country,
A land of sweeping plains,
Of ragged mountain ranges,
Of droughts and flooding rains.

The failure to properly assess the risks and take appropriate action can lead to serious consequences
The failure to properly assess the risks and take appropriate action can lead to serious consequences

As I write we are experiencing the flooding rains with water now covering many of our ‘sweeping plains’, which of course brings all sorts of risks that need assessment. This can be on a major scale for the emergency services or on an individual level when we are confronted with high water situations, often entailing the need to assess the risk and determine a course of action. The failure to properly assess the risks and take appropriate action can lead to serious consequences, including death.

I was struck by this on a small scale recently when I took a newcomer out for her first canyon trip. The canyon was flowing very fast and the 30 metre waterfall (see picture) we had to abseil down at the end was a huge gush of water belting down onto the cliff face partway down and then cascading into a deep pool at the bottom. It is very difficult to keep your feet and even to breathe in these situations with the water pounding on your head and body. I had to assess the risks to my new recruit and to make a decision if she was up to it.

I am a canyon instructor and so hopefully I have the competencies for this task. I did decide to proceed with appropriate control measures in place and she survived the experience alive. But there were some anxious moments while I waited for her to appear from under the waterfall and she did end up with some impressive bruises to show her friends! I got off a little more lightly.

Risk assessment in TC 31

The concept of risk assessment is starting to appear in many aspects of what we do. This is now particularly true for IEC committee TC 31. There are three areas of our work which I would like to address:
1. The provision for risk assessment associated with the introduction of equipment protection levels (EPLs).
2. Ignition hazard assessment in the new standard on Ex ‘s’ special protection.
3. Ignition hazard assessment in the new standards for non-electrical equipment.

Equipment protection levels

Equipment protection levels (EPLs) were introduced into the TC 31 a few years back, derived from the category requirements for ATEX. The definition of EPL is contained in the general requirements document IEC 60079-0 as follows:
Level of protection assigned to equipment based on its likelihood of becoming a source of ignition and distinguishing the differences between explosive gas atmospheres, explosive dust atmospheres, and the explosive atmospheres in mines susceptible to firedamp
NOTE: The equipment protection level may optionally be employed as part of a complete risk assessment of an installation, see IEC 60079-14.

The note above references the risk assessment process. What the introduction of EPLs did was to break the hard link between equipment protection techniques and the zones determined in area classification. However, it is important to understand that the use of EPLs was introduced as an alternative to that approach, not a replacement. The EPLs give you a measure of the confidence that you can have in an item of equipment not to cause an explosion. EPLs are always assigned to the equipment and the risk assessment can determine its appropriateness for a particular situation. However, as a result of a risk assessment, the area classification documentation may show the EPL that is required for a particular area. IEC 60079-10-1 (Clause 4.2) on classification for explosive gas atmospheres describes the situation as follows:

Subsequent to the completion of the area classification, a risk assessment may be carried out to assess whether the consequences of ignition of an explosive atmosphere requires the use of equipment of a higher equipment protection level (EPL) or may justify the use of equipment with a lower equipment protection level than normally required. The EPL requirements may be recorded, as appropriate, on the area classification documents and drawings to allow proper selection of equipment.

The installation standard IEC 60079-14 then describes the process regarding the relationship between EPLs and zones in Clause 5.3. It includes a table (Table 1) showing the direct relationship between zones and EPLs, and also includes a note in this clause that provides guidance as follows:

As an alternative to the relationship given in Table 1 between EPLs and zones, EPLs may be determined on the basis of risk, i.e. taking into account the consequences of an ignition. This may, under certain circumstances, require a higher EPL or permit a lower EPL than the defined in Table 1.

As examples of the approach referenced in the above, you could have an area that is classified as Zone 1, but as a result of the risk assessment it is decided to only accept equipment that has an EPL of Ga which would normally only be required for Zone 0.  Conversely, another area with a classification of Zone 1 might be assessed as only requiring equipment with an EPL of Gc, not Gb as would normally be required.  

Equipment protection by special protection “s”

It is expected that a new standard IEC 60079-33 Ed. 1.0: Explosive atmospheres – Part 33: Equipment protection by special protection “s” will be published later this year.  

This standard was developed as a result of a request from IECEx to provide a set of requirements to be used for certification within the IECEx Product Certification Scheme when the standards for existing types of protection were not applicable. It will allow a design concept that cannot comply in full with recognized types of protection or where the design concept is not covered by recognized types of protection. The first edition of the standard will only apply to electrical equipment.

A feature of this standard will be the introduction of ‘ignition hazard assessment’. A formal documented hazard assessment will have to be prepared by the manufacturer, identifying and listing the potential sources of ignition by the equipment, and the protective measures to be applied. This is the first time that risk assessment has been introduced into an IEC standard for electrical equipment design.

Non-electrical equipment

A sub-committee of TC 31, SC 31M Non-electrical equipment and protective systems for explosive atmospheres, has been making good progress to develop of standards for non-electrical equipment. One the important standards being developed is ISO 80079-36 Explosive atmospheres – Part 36: Non-electrical equipment for explosive atmospheres — Basic method and requirements.  

This standard has been through a number of committee drafts and will soon be issued as a committee draft for voting.  Hence the technical requirements in this standard are now well defined. It specifies the basic method and requirements for design, construction, testing and marking of non-electrical equipment and Ex Components intended for explosive atmospheres.  

It supplements and modifies the general requirements of the general requirements document IEC 60079-0. However, it contains a critical feature that is not in that standard, that is the requirement for an ignition hazard assessment. The outcome of ignition hazard assessment must confirm that the equipment does not contain any effective ignition sources. The assessment may look at normal operation, expected malfunctions or rare malfunctions. This will then affect the EPL that can be assigned to the equipment. The ignition hazard assessment must be formally documented and identify all potential ignition sources that could occur during normal operation and malfunctions as shown above.

References:
1. IEC 60079-0 Explosive atmospheres – Part 0: Equipment – General requirements
2. IEC 60079-10-1 Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas atmospheres
3. IEC 60079-14 Explosive atmospheres – Part 14: Electrical installations design, selection and erection
4. Draft IEC 60079-33 Explosive atmospheres – Part 33: Equipment protection by special protection “s”
5. Draft ISO 80079-36 Explosive atmospheres – Part 36: Non-electrical equipment for explosive atmospheres — Basic method and requirements



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