Any industry that processes, uses or manufactures materials that may give rise to a flammable atmosphere (gas, mist, liquid, dusts or even small fibres) may have a potentially explosive atmosphere. Where fuel and oxygen (normally the oxygen in air) are present in the workplace, potential ignition sources must be rendered safe to an acceptable level for the risk.
Typical industries that fall into this category includes; Oil and gas processing, gas and coal power stations, paint spraying, chemical processing, fertiliser plants, oil and gas - drilling and refining, aviation and airports, water treatment and sewerage.
In order to make electrical equipment safe for use in a potentially explosive atmosphere, some form of protection must be afforded. Irrespective of 
whether you are certifying equipment for the ATEX Directive (for use in Europe) or to international requirements, the fundamental methodologies remain the same. One of the most commonly used concepts for low power equipment (such as instrumentation) is 'Intrinsic Safety'.
Potential explosion risks;
Open circuit or short circuit components or interconnections in a resistive circuit
Short circuit of components or interconnections in a capacitive circuit
Open circuit components or interconnections in an inductive circuit
Ignition by hot surfaces.
So, back to the question asked in the headline of this blog post; ATEX Insulation Testers - Do They Exist?
I found this on from the IET Forums;
The protection concept of intrinsic safety (Ex 'i') is based on the equipment and/or circuit not having sufficient energy to ignite a specified potentially explosive atmosphere. As such, it is not possible to design intrinsically safe versions of instruments commonly used in the testing of electrical installations as the energies involved far exceed those normally associated with the protection concept of intrinsic safety.
Intrinsically safe insulation and continuity testers are available, but those which I have seen have been certified to the now obsolete BS 1259 : 1958 - Intrinsically safe electrical apparatus and circuits for use in explosive atmospheres. Instruments certified to this standard are intrinsically safe only as a single piece of apparatus without consideration as to the circuits in which they may be connected. Whilst the sparking created when the instrument terminals or test leads are is safe in atmospheres of the classes for which the instrument is certified, but the sparking which may occur in a circuit under test may have energy greater than that which is safe in the given atmosphere by way of the capacitance and inductance of the circuit under test.
Instruments, such as multimeters, certified to later standards for intrinsic safety are generally marked with the maximum permissible parameters of the circuits to which if may be connected, but to date I have not seen an insulation and continuity tester certified to any other standard than BS 1259.
The BS 1259: 1958 standard that the poster was refering to covered the Metrohm 7A501C safety tester, a 500V insulation tester that became almost the industry standard in places such as mines and petrol sites. Although still available, it is now only for sale where the intended use is outside the EU.
Metrohm 7A501C Safety Insulation tester
For many years (over 45 in fact), the Metrohm 7A501C was used in hazard areas in this country. And in the last 40 years there have been no accidents reported attributable to the use of a 7A501C in explosive atmospheres. BS1259 is now obsolescent and has been superseded by BS5501. Under BS1259 the tester by itself was approved whereas under BS5501 approvals also consider applications of the tester. For example when carrying out insulation testing at 500V DC on wiring installations the inherent self-capacitance of the wiring will charge up and could create an incendive spark if discharged accidentally. It is necessary therefore to have a good working code of practice so that this hazard is eliminated and to ensure that the charge held in the wiring capacitance is discharged safely via the tester at the end of each insulation test.
Features of th
e 7A 501C:
- Tautband analogue meter.
- Insulation: 500V DC 0-50MΩ.
- Continuity: 0 to 50Ω.
- Not ATEX approved.
- Safety: Complies With: BS1259.
- Test Leads: 1m long with crocodile clips.
- Dimensions: 132 x 82 x 60mm.
- Weight: 0.6Kg.
View the Metrohm 7A501C Safety Insulation Tester here
Tietzsch MegaSafe ISO 1Ex - 500V Megohmmeter for Ex-areas
As an authorised distributor of Martindale products (who now manufacture the Metrohm 7A501C), we are often asked if we can supply an ATEX Insulation tester. Well the answer is yes, the MegaSafe ISO 1Ex. The Tietzsch MegaSafe ISO 1Ex is a high-voltage testing device for safe testing of insulating resistances up to 2GΩ, with test voltages of 32V up to 500V and with a digital read out system. The device is external voltage-proof up to 500V. It has an integrated protective series resistor of 500kΩ for safe application in Ex areas.
Technical Data & Features: High-impedance megohmmeter OMegaSafe ISO 1Ex in accordance to EN/IEC 61010-1 and EN/IEC 61557-2 (VDE 0413 part 2) Ex protected design in accordance to EN 60079-0 und EN 60079-11. EC Type Examination Certificate: II 2 G Ex ib IIBT4 BVS 06 ATEX E130.
Features of the MegaSafe Iso:
- Test Voltage: 32, 100 & 500V.
- Safe and universal between 1 k Ω and 2 TΩ.
- Test voltage selection per push-button.
- Push-button for quick discharge of capacitances.
- Simultaneous indication of test voltage and resistance value.
- Test voltage: 32, 100, 500V.
- Voltage Indication: red LED and acustic warning signal as well as indication of the value in Volts.
- Accurracy: 5% +/- 5 digit at 20°C.
- Display: 2-line LCD-display, 3 ½ digit.
- Power Supply: battery 9 V-block AlMn IEC 6LR61.
- Casing: made of impact resistant ABS with unbreakable display cover, antistatic coated.
- Protection: IP 65, device can be used in moist environments.
- Dimensions: 60 x 230 x 40mm.
- Weight: 220 g.
View the Tietzsch MegaSafe ISO 1Ex here
THESE INSTRUMENTS SHOULD ONLY BE USED BY A COMPETENT, SUITABLY TRAINED PERSON.