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I'm wondering whether anyone has some experience with designing electronics for compliance to IEC 60079 Explosive Atmospheres. I have designed a device to be installed in silos facilities which are considered explosive atmospheres due to fine dust present in the air. I have been given IEC 60079-7 - Explosive Protection by increased safety "e" and told that the device must be proven to comply with it.

I have read IEC 60079-0 and 60079-7 and since the device does not contain heaters, luminaries, motors or transformers, most of it is not applicable. The device takes 9V DC and works at 5V DC, has no-burn fuses and Zener diodes for overvoltage protection and ESD devices against ESD discharges.

The two questions I have is whether anyone has any experience working within IEC 60079 to give me some examples of things to look out for to comply with this standard? Secondly, from reading 60079-0 section 29.3 it does not mention the possibility of using "increased safety e" in Group III (dust) atmospheres which confuses me - is increased safety e compatible with Group III dust atmospheres (i.e. can we implement increased safety for Group III devices or not?) I find the whole standard very confusing and sometimes ridiculous (apparently one of the tests I need to pass is a 1kg weight being dropped repeatedly onto the device!!!) . Long story short: 1) Any things to look out for or examples to follow to comply with IEC 60079? 2) Can a device implementing increased safety "e" be used in explosive dust atmospheres (Group III) or is safety to be achieved only through enclosure, encapsulation, intrinsic safety and pressurization?

Thanks, any tips on implementing IEC 60079 compliance is welcome.

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    \$\begingroup\$ You may find the 1kg weight thing silly, but it's quite sensible really - it's not to test the impact resistance to the weight per se, but to check that the device is still compliant after being smashed around in an industrial environment. Are seals still intact, casing not cracked, internals not sheared away and causing short / spark hazards, etc. All important tests. \$\endgroup\$ – Majenko Nov 5 '14 at 10:53
  • \$\begingroup\$ You say a lot about what "the device" doesn't contain but nothing about what it does contain. \$\endgroup\$ – Andy aka Nov 5 '14 at 13:01
  • \$\begingroup\$ The device contains a 1A fuse, 15V zener for overvoltage protection, 10Ohm power resistor to limit current into the device (assuming fuse fails short somehow), a couple of 5V linear regs (fused separately with 0.5A fuses), an MCU with RS485, RS422 interface, and 30 terminal block connectors for connecting digital sensors, each connector line to MCU us ESD protected, inline resistor to limit current, and that's it. The maximum power that can enter the device assuming a horrible fault of some kind, Vin=15V (after which zener triggers, Iin=1A (above which fuse breaks), P=15*1=15W. \$\endgroup\$ – IgorEE Nov 5 '14 at 13:16
  • \$\begingroup\$ I can't speak to that standard specifically, but the concern is sparking, high temperatures and thus possible ignition. So the right way to think of it is, limiting the current is one thing, but even limited power can spike up to high temperatures if the energy concentration is high and there is thermal insulation. So a current limiting resistor is good, but under fault conditions it should have limited temperature rise. A small resistor is very clearly out spec here. As @Majenko-notGoogle points out, hitting it to ensure that you don't get shorts and hot spots etc. etc. is a good test. \$\endgroup\$ – placeholder Nov 5 '14 at 15:41
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It is always case dependent. Not only with IEC 60079. For general, there are my seven "NOs":

1) no thermal chokes (enclosure/surface temp growth up/down too high)

2) no thermal differential (enclosure/surface temp inequality)

3) no electrical sparks (while connecting power, on, off, etc)

4) no vibration (with freq/mags sensible by the environment)

5) no electric/magnetic fields (with params sensible by the environment)

6) no focused irradiation (ir, uv, others sensible by the environment)

7) no other stimuli you find sensible by the environment

How to design such devices?

When you are facing safety problem, you need to analyze

  1. the environment you need to operate in,
  2. the scenario(s) how your device interacts (within) the environment
  3. the factor(s) and direction(s) your devices impacts the environment with
  4. the limits the impact is insensible (safe) for the environment

When you know this, next you harmonize your (initial) design step-by-step, trial-and-error (trial-and-error-and-error-and-error :-] depending on the experience your have/can access) to the state in which:

  • its impact to the environment does not exceed the safety limits and/or
  • its behavior does not predictably run out of safety enabled scenarios

My notice for you is the following:

1) read all the parts of the standard series, beginning from the first, to get better understanding of the safety regulation approach and details

2) read some books related to the standard (generally standards authors like to write related books because they give them money and additional points in the science world :-)

3) read information about similar devices, buy one or two and examine, but have a respect for third-party's intellectual property, of course.

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