Ex FAQ explosion protection R. STAHL


Frequently asked questions about explosion protection

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

The answer is "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.

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More FAQs for your safety

1. 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.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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 d 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.

9. 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.

10. 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.