Ex FAQ explosion protection R. STAHL

FAQ – YOUR QUESTIONS, OUR ANSWERS

Frequently asked questions about explosion protection

Can only low-sparking tools be used in hazardous areas?

Sparks generated mechanically by processes involving friction, impacts, grinding or drilling represent sources of ignition as per EN 1127-1. Whether and to what extent the formation of sparks caused by the use of tools is permissible depends on the corresponding protective zone and the ignitability of the explosive substances. In Zones 0 and 20, no tools that could generate any sparks may be used.

Stainless steel tools such as screwdrivers or wrenches, which typically generate only a single spark when used, but which do not generate any bursts of sparks or hot surfaces, may be used in Zones 1 and 2. However, this does not apply for Zone 1 if there is an explosion hazard in the zone caused by substances in explosion group IIC (acetylene, carbon disulphide and hydrogen) or due to hydrogen sulphide, carbon monoxide or ethylene oxide. In this case, special measures to prevent the generation of ignitable sparks must be taken.

In Zones 21 and 22, the use of stainless steel tools that do not generate any bursts of sparks or hot surfaces is generally permitted. If this cannot be guaranteed, the workplace must be cleared of all dust deposits and shielded to separate it from the surrounding zone area. Additionally, it must be kept humid while the tools are being used, in order to prevent dust from being thrown up and glowing embers from being produced.

Low-sparking tools are therefore not permitted in hazardous areas as a rule. In individual cases, however, they can be practical. However, a risk assessment of the operation is always required.

Ex Tools Hazardous Areas R. STAHL

More FAQs for your safety

1. Can a device with a label for gas and dust be used freely in atmospheres that contain both gas and dust?

Where combustible dusts and combustible gases or vapours are present, this is referred to as a hybrid mixture. These types of hybrid mixtures can have critical key characteristics that differ from the individual substances. The IEC 60079-14 standard, appendix M, contains some information that should be taken into account. As, in practice, the situation can present itself very differently, a risk assessment must be performed in order to determine suitable measures. Devices that are approved for both gas and dust hazardous areas may therefore not be used freely in areas with a hybrid mixtures.

The protective measures for the devices (one for gases and one for dusts) do not necessarily exclude combinations. This, for instance, is how the temperature class is determined for a device approved for operation in gas atmospheres with no deposited dust layer. However, dust deposits increase the surface temperature of an enclosure or the installed devices, and therefore also the explosion hazard. In the case of flameproof enclosures that are exposed to hybrid mixtures, there is a risk of dust deposits in ignition puncture-proof joints, which may be ejected as hot particles in the event of an internal explosion, thereby posing an ignition hazard. For these reasons, a special assessment and inspection is required when using explosion-protected devices in an environment with hybrid mixtures.

2. Can a device that is approved for gas hazardous areas also be used in dust hazardous areas with no additional measures?

No. This is because different requirements apply to devices in different atmospheres. For instance, in the case of terminal boxes with Ex e protection (increased safety), IP protection of at least IP 54 is required – for dust hazardous areas, IP 6X is required. In the same way, hermetically sealed enclosures (Ex d) in dust hazardous areas can cause problems if dust is deposited in the joints.

3. Do hazardous areas always have to be divided into zones when there is an explosive atmosphere?

If an explosive atmosphere is created, the area does not necessarily need to be divided into zones. Zone classification into Zones 0, 1 and 2 for gas, mist and vapour atmospheres and Zones 20, 21 and 22 for ignitable dust atmospheres is designed for areas in which there is a certain probability of an explosive atmosphere being created that could be ignited by a source of ignition, causing an explosion.

The required protection level of the devices is determined by the probability of an explosive mixture being created. If the explosive atmosphere is only present at very specific, precisely predictable times – for example when opening a container – a protective zone does not have to be assigned. Instead, as part of a risk assessment, specific protective measures can be implemented for the time in which the hazard is present.

4. Do temperature classes and groups need to be observed in Zone 2?

Even if the probability of an explosive atmosphere being created is low, temperature classes and groups must be observed. These always play a role in the selection of devices in hazardous areas, as the specifications relate to potential sources of ignition in the form of hot surfaces or ignitable energy.

The maximum surface temperature of electrical equipment must always be lower than the ignition temperature of the gas/air or vapour/air mixture in which the device is used. Some devices are approved for T6 temperature class and therefore for operation in an environment with gases and vapours with ignition temperatures between +85 °C and +100 °C. In these environments, the surface temperature must not exceed +85 °C. The lowest temperature class, T1, permits use in areas with gases or vapours that can only be ignited at temperatures over +450 °C.

Gases, vapours, mists and dusts are subdivided into various groups according to their characteristics. To make this easier and to ensure the correct selection of equipment, these are assigned to relevant material groups. The equipment groups and temperature classes therefore describe the level of protection and the application range of the devices. According to IEC 60079-0, the devices are classified for all gas hazardous areas (except mines susceptible to firedamp) into groups IIA (e.g. propane), IIB (e.g. ethylene) and IIC (e.g. hydrogen). Both the temperature classes and the group classification must be observed in all zones.

5. Can smartphones with built-in batteries be taken into the hazardous area?

No, a smartphone is a device according to the ATEX directive and requires approval. Devices without approval, regardless of whether they have a built-in battery, may not be taken into areas with explosive atmospheres.

The reason for this is that mobile phones generate electromagnetic fields that can, for instance, heat up small metal components. This means that there is a risk of these components becoming a source of ignition. The EN 60079-14 standard specifies the peak power up to which the electromagnetic field generated by a smartphone is considered not to be a source of ignition.

Mobile phone cases also pose a potential hazard. These are often made of plastic which can become electrostatically charged. This can cause electrostatic discharge, meaning that the mobile phone case becomes a potential source of ignition.

6. Are small electrical devices such as watches, pocket calculators or hearing aids potential sources of ignition? If so, must they be kept outside hazardous areas?

In the case of watches, due to their enclosure size and design, the Komitee 235 group belonging to the German Electrotechnical Commission has stated that no explosive atmosphere can penetrate a watch, even taking particularly unfavourable circumstances into account. As a result, electrically powered watches with no additional special functions (e.g. a calculator function) pose no explosion hazard in Zones 1 and 2. Wall clocks, in contrast, must be designed to be explosion-protected (for instance with II 2 G Ex e mb IIC T6 label).

When it comes to hearing aids, both the battery voltage and any ignitable inductive electrical circuits must be taken into account. In any case, the ignition hazard posed by compact devices worn in the ear is deemed to be low enough that they can be worn in Zones 1 and 2. Associated remote operation devices are excluded from this rule.

The use of pocket calculators in hazardous areas requires a case-by-case inspection and approval process, even for solar-powered devices, because ignitable voltages can be generated above a certain number of solar cells.

7. Can smart watches be taken into hazardous areas?

Smart watches, fitness watches, GPS watches and similar devices feature a number of special functions, including calculators, wireless connections via Bluetooth, and more. They are therefore not permitted for use in hazardous areas.

8. What does the "U" after the certificate number on the test certificate for a device mean?

The "U" ending on test certificates such as PTB 09 ATEX 1107 U means that the device in question is incomplete equipment. A partial certificate of this kind, as is issued for empty enclosures, for instance, does not certify complete devices, but only partial components. Why? Because (in the case of empty enclosures) the inspection is limited to just the enclosure characteristics and the operating instructions relate only to the empty enclosure.

Inspections for the "increased safety" (Ex e) type of protection, for example, include testing the leak-tightness and strength of the enclosure and the thermal resistance of the materials used. This partial test certificate is therefore only used as a basis for certifying the entire device.

If the device already has an incomplete test certificate of this kind, the manufacturer of the complete device no longer has to test the enclosure characteristics in-house. However, the complete device requires a complete test certificate that includes the temperature resistance and other data, including the installation conditions and the type and number of installed components.

9. What does it mean when a certificate has an "X"?

The "X" ending – as in PTB 09 ATEX 1109 X – indicates that special conditions must be taken into account when installing, operating and/or inspecting the device. These are noted in the operating instructions. The device is only explosion-protected if these conditions are met.

10. Does "Ex" always mean the same thing?

No – the correct "Ex" differs. For instance, Ex d enclosures must be able to withstand an internal explosion. They must therefore not be fitted with stopping plugs made of plastic. These components cannot be granted Ex d approval – but they do have Ex e approval, which certifies that the enclosure is leak-tight and impact resistant. Plastic stopping plugs (Ex e) are not tested for pressure resistance. As a result, they will not withstand an internal explosion.

11. Can terminals be retrofitted by the customer on Ex e terminal boxes?

Yes. However, when retrofitting the terminals, you must comply with the manufacturer's operating instructions. This means that you may only use terminals that the manufacturer has included in their certificate (e.g. made by certain manufacturers, of specific size or classification). Additionally, the terminals require a U certificate, as they must be certified as Ex e components. Why? Because the terminal boxes must be tested with regard to these terminals. Furthermore, you may only retrofit a certain number of terminals. The maximum number is also specified in the operating instructions.

12. Can drilled holes and screw connections be retrofitted by the customer on Ex e terminal boxes?

This is permitted – after consulting the manufacturer. The manufacturer's operating instructions specify the requirements – i.e. how many drilled holes to create on which sides and of what size, as well as the gaps between them, in order to guarantee stability. However, any retrofitting work performed is the customer's own responsibility and must be tested by them.

13. Is it possible to use Ex d cable glands and Ex d stopping plugs in Ex e enclosures?

Hermetically sealed screw connections and hermetically sealed stopping plugs can also be fitted in Ex e enclosures. According to applicable standards, these components are approved for use in Ex e enclosures. However, the reverse does not apply.

However, plastic enclosures (Ex e) with screw connections and metal stopping plugs (Ex d) must be earthed to eliminate any voltage transfer to the enclosure.

14. Do Ex d cable entries need to be sealed using a compound?

The use of a screw connection with a compound is only necessary if the following requirements have not been met:
- The cable entry must be certified for Ex d.
- The cable and the electrical lines must comply with the requirements in the standard.
- The minimum length of the connected cable and electrical lines must be three metres.

15. How many Ex d adapters can be used with an Ex d cable entry?

Only one adapter can be used with an Ex d cable entry in order to maintain guaranteed pressure resistance. This is because adapters represent additional volume that can cause pressure to build up inside the enclosure.

No adapters may be used with stopping plugs. The stopping plugs must be fitted directly into the housing.