Ex-PERT Guide to Buying Equipment for Hazardous Areas

Selecting equipment for hazardous areas can be a daunting task, and it is vital that a number of factors are considered when making these decisions. This guide is designed to make the process easier, and to ensure that all bases are covered from an Ex perspective.

Ex Certification – The Basics

Knowing what certification is required may be an obvious step, but it should not be taken for granted. For Europe you will require ATEX certified equipment for hazardous areas and they should have followed the relevant assessment routes for design and quality conformity.

You should also take into account whether the equipment is being fitted to a moving destination, for example an FPSO (Floating Production Storage and Offloading vessel) or a portable skid. If it is then the IECEx mark may well be required, along with potentially other certification such as TR CU (Russia) and INMETRO (Brazil) to match the corresponding territories that the equipment will enter. You will need to familiarise yourself with these certification requirements if you are involved in purchasing equipment for such destinations.

Ex-PERT Guide to Buying Equipment for Hazardous Areas

An important consideration should also be whether there any other stipulations for the product; for example is the equipment to form part of a Safety System and as such has a SIL (Safety Integrity Level) rating been called for?

It is also vital to be aware of any special conditions of safe use – this is easy to identify as there will an X at the end of the ATEX certificate number. It is quite common to find these conditions attached to Ex equipment but it is essential to know what they are prior to purchase as they may restrict how you use the equipment, for example the orientation and fixing of the equipment, earthing arrangement requirements, and stipulations with regards to the power supply.

Likewise, it is important to identify equipment marked with a U at the end of the ATEX certificate number as being only component certified and therefore the component cannot be used without further assessment and certification as part of a larger unit or system. This is often the case for products such as breathers for use on Ex d boxes, whereby they must also be assessed as part of the overall design.

The Environment

There are a number of factors to consider when we talk about the environment. Firstly let’s cover the explosive elements and the markings required for each:

1. For ATEX equipment, products are grouped into two categories: I = Underground or II = Above GroundThis should be a very straightforward decision to make.

2. For Group II, is the equipment going to be exposed to potentially explosive gases (G) or potentially explosive dusts (D)? In some rare applications you may find that equipment is exposed to both – certain pharmaceutical products and processes are a good example of this.

3. GAS AND DUST GROUPS - It is not enough to know whether the explosive atmosphere is Gas or Dust - you must also consider the Gas Group or Dust Group in which the explosive material falls (Group II only) and select equipment accordingly.

4. TEMPERATURE CLASS - Explosive gases and dusts have an ignition temperature which is the point at which given the right conditions, it will ignite. This is where (for Group II Equipment) the importance of selecting the right temperature class is required. Consider what are the ignition temperatures of the material found in the hazardous locations? Your Hazardous Material Datasheet should contain this information and should be matched against the equipment’s T Class.

Group Enviroment Location Typical Substance

I

Gases, Vapours and mists

Coal Mining Mehane ( Fire Damp )

IIA

Surface and other mines

Methane, Propane etc.

IIB Ethylene

IIC Hydrogen, Acetylene etc.

IIIA

Combustible Dust Surface

Combustible flying’s

IIIB Non-conductive

IIIC Conductive

5. AMBIENT TEMPERATURE - There is a second part to consider when looking at temperatures and that is ambient temperature; the climatic temperature range that is going to be in the hazardous location all year round. Hazardous areas in the UK where -20°C to +40°C may be acceptable would not for example be suitable for a hot Middle-Eastern country where the upper ambient could be higher or Russia where the lower ambient could need to be lower.

6. ZONES - One of the biggest considerations when providing a specification for equipment is what zone will the equipment be placed into, and therefore what level of protection is the equipment to have. The below table best explains the relationship between categories, zones and equipment protection levels:

7. PROTECTION CONCEPT - Equipment is usually designed to conform to one or more protection concepts in order to ensure its safe use in a hazardous area. The design principles behind the concepts vary greatly and they may hold some bearing on your selection of equipment as it will affect requirements (such as the installation). It is important to note that protection concepts are not all suitable for every zone, and so for example searching for an Ex d Zone 0 product will be unlikely to produce results as Ex d is typically suitable for Zone 1 and 2 only.

Temperature Class ( Group II )

Maximum surface temperature T. Codes

450°C T1

300°C T2

200°C T3

135°C T4

100°C T5

85°C T6

Equipment Group Category Zone of use Equipment Protection Level

I M1 NA Ma

I M2 NA Mb

II 1 0/20 Ga/Da

II 2 1/21 Gb/Db

II 3 2/22 Gc/Dc

There are also other environmental factors that need to be considered:

1. INGRESS PROTECTION. Ingress protection is relevant in the selection of both Ex and non-Ex equipment. The difference is that for some Ex equipment a minimum IP rating is mandatory as part of the Ex protection concept, irrelevant of whether the customer requires that level of ingress protection or not.

2. CORROSION. Industrial environments can be harsh on equipment, and some applications such as our North Sea platforms for example have additional challenges when it comes to corrosion. Corrosion is often one of the main considerations during scheduled inspection of plant and can be a costly factor in terms of maintenance and replacement. And it is not always easy to remedy corrosion to Ex equipment as coatings are often controlled as part of the certification, and rubbing down and repainting can for example compromise something such as a flamepath. Therefore considering the harshness of the environment and correctly selecting suitably protected equipment to match is important.

3. FORCES. Some equipment is, by its nature, exposed to harsh handling, mechanical vibration or dropping. An example of this would be portable equipment such as hand lamps and radios. Equipment like this should have gone through more stringent drop tests and impact testing to ensure that it can meet the demands of the job. You should always use equipment designed for the purpose that it was intended, and discuss with the manufacturer the type of use the equipment will be subjected to before purchase.

Ingress Protection CodesFirst Number ( Protect from solid bodies ) Second Number ( Protect from water )

0 No protection 0 No Protection1 Objects > 50mm 1 Vertical drip2 Objects > 12.5mm 2 Angled drip3 Objects > 2.5mm 3 Spraying4 Objects > 1.0mm 4 Splashing5 Dust-protected 5 Jetting6 Dust-tight 6 Powerful jetting

7 Temporary immersion8 Continuous immersion

Specific Equipment RequirementsDifferent products require different considerations and we have called upon some experts to provide guidance….

When considering Medium and High voltage cable termination in hazardous areas it is important to consider the following in your specification:

• Maximum operating voltage• Expected full load phase current (this will be line current /√3 if wired in delta) (start-up current is ignored)• Number of conductors per phase incoming and outgoing, and their cross sectional area• Number of cables incoming and outgoing• Details of any neutral conductors• Details of any earth (ground) conductors, and should this include a connection to the enclosure housing?• Diameter over conductor core insulation• Minimum bending radius of all the conductor cores (not the overall cable) including neutrals and earth conductors• Conductor shield earthing (grounding) requirements• Desired enclosure entry sizes and positions (i.e. top, bottom, left or right hand sides)• Any specific requirements for threaded entry bosses• Any specific requirements for door interlocks (Fortress, Castell, etc)• Any special requirements for enclosure finish, such as painting or electro-polishing• Any specific requirements for enclosure mounting strap positions• In some instances there is also a need to include an anti-condensation heater. If this is the case then how it will be powered should also be a consideration.

Medium and High voltage cable termination

www.abtech.eu

www.e2s.com

Three important things to note when considering warning signalling equipment:

• Intrinsically safe Signalling devices: because of their relatively low level sound and/or light outputs, are usually most appropriate for indoor applications.

• Beacons and Status Lights: The application (required output light level and operation cycle time and length) will often determine choice of either Xenon strobe or LED technology.

• Alarm Sounders: The sound level needs to be at least 5 dB above the background noise and the selection of appropriate output tone is very important, with a changing frequency, e.g., ‘sweep’ type, being particularly effective at gaining attention.

Warning Signals

Purged and pressurised enclosures provide a flexible solution to installation requirements, with the following considerations:

• Heat loading in the enclosure. It is worth considering both the internal load as well as the sole load. Ex p enclosures are fully sealed and therefore often have higher cooling requirements than normal.

• Components forming part of the enclosure, such as lamps and push buttons need to be certified in their own right - Ex p can only protect what is physically inside.

• Internal sources of release, specifically for analysers, needs consideration. Are you bringing a source of flammable fluid into the enclosure? This is allowed but makes for a more complex assessment.

• Isolation of equipment. When pressurisation is lost all non-certified electrical equipment must be isolated. Doing this as an afterthought to the design can be troublesome. Specially here looking about incoming powered signals, LAN, Ethernet cables or any other non Ex signal.

• Batteries need special assessment. They can be fitted but need to be assessed. Batteries are in many devices as back up memory power sources. Highlighting this early on in the design allows for replacements with approved batteries or back up power sources.

Purged and Pressurised Enclosures

Three important things to note when considering your lighting options:

• When retrofitting, specify from the demands of the application, not from the specification of the existing product that’s installed. As an example people often assume that they need a T6 fitting, simply because they have an existing unit which is T6 rated, whereas in reality T4 would be sufficient – specifying the correct product could provide benefits such as cost savings or shorter lead times.

• Select a maintenance friendly solution – the real cost of a light fitting comes from the medium to long term cost of maintaining and servicing it. A modular design which allows maintenance to be carried out on-site is advantageous, makes it far easier and cheaper when it is required, and minimises downtime of the light fitting.

• Consider the demands of the application when selecting your lighting technology, for example is the lighting going to be exposed to extreme temperatures? Some technology suffers significantly (lumen output may drop, emergency functions may fail) whereas the performance of lighting such as LED remains consistent. Is it being positioned in a more difficult to reach location? If so you should consider a solution that minimises maintenance and servicing; an example would be the use of LED technology where relamping is not required.

Lighting

www.expoworldwide.com

www.raytecled.com

There are both operational and inherent commercial considerations when planning your digital display requirements:

• When selecting field or panel mounting display instrumentation for use in a potentially flammable atmosphere, there are safety and economic advantages resulting from trying to locate it in the least hazardous Zone possible. It is preferable for operators to view an instrument in Zone 2 than in Zone 1, and Zone 2 instrumentation is often less expensive to purchase and install than that certified for use in Zone 1. If the measurement is to be made in Zone 0 or Zone 1, it is still worth trying to locate the display in Zone 2. For example, selecting an Ex nA non-sparking indicating transmitter with an Ex i intrinsically safe input, allows the transmitter incorporating a display to be located in Zone 2, with the resistance thermometer or thermocouple in Zone 0 or Zone 1.

• When installing instrumentation incorporating a display, be it a flow transmitter or an HMI, it should obviously be positioned where it can easily be seen by the operator, but the instrument’s display technology should also be considered. Light emitting displays (LEDs) will be swamped by bright sunlight. Liquid crystal displays (LCDs), be they reflective or transmissive, are usually enhanced by bright sunlight, however they may have a preferred viewing direction. Manufactures instruction manuals often recommend a viewing position. If possible it is best to avoid positioning any type of instrument display In continuous direct sunlight.

• Most manufacturers of field and panel mounting hazardous area instrumentation design and test their products to ensure performance and safety are not degraded by the ingress of water and dust. Fitting of an incorrect gland or blanking plug, or cutting an incorrect size aperture for a panel mounting instrument can negate this work and result in an unsafe installation, degraded performance or premature instrument failure. Again reading the instrument instruction manual should prevent problems developing.

Commentary and other materials posted on this guide, and links to specific products or suppliers, are not

intended to amount to advice on which reliance should be placed. We therefore disclaim all liability and

responsibility arising from any reliance placed on such materials by any person who reads this material,

or by anyone who may be informed of any of its contents. We do not couch for the accuracy or suitability

of this guide when selecting any products for any specific uses. Independent guidance should always be

sought.

Display Instrumentation

www.beka.co.uk