Mobile devices in Hazardous Areas. Written by Gary Friend PrEng CEng. gary@extech.co.za; +27 83 3098200/+44 7711402474

(Picture courtesy of i.safe MOBILE)

Introduction:

The intention of this paper is to outline the basic requirements to design & manufacture an IS mobile device. What are the risks & what do the standards say. This will hopefully explain why IS mobile devices are more expensive than standard rugged devices. This is not intended to be a design guide or a Promotional presentation. I have selected 5 areas, where the requirements of IS are important & substantial to avoid ignition. All references are to SANS 60079-11:2012 (based on IEC 60079-11:2011) unless otherwise stated. Note that IEC 60079-11:2023 has recently been released & SANS will follow in time.

Please note that excerpts of SANS60079-11:2012 are for illustration purposes only and have been included to provide context & evidence of comments. Only small relevant sections of the 149 page document are shown. The references illustrate the sections referred to and allow the reader to refer to relevant sections of the standard to be read in full, to obtain a complete understanding of the subject matter at hand.  For your ease of reference, the standard can be purchased at https://store.sabs.co.za/sans-60079-11-2012-ed-4-00.html

1. The battery itself is the largest risk (see 7.4 for battery selection, suitability & specific requirements for IS). Battery design, short circuits, overheating, how the battery is charged are key. This includes battery charge connectivity (USB & magnetic charge terminals).

Battery construction is defined in SANS/IEC60079-11 7.4.2 and extensive & destructive testing is defined in 10.5.3. Spark ignition tests are comprehensive defined in 10.1 & temperature tests defined in 10.2.

SANS/IEC60079-11 6.2.5 defines the requirements for battery segregation & charging. Even if charging is carried out in the non-hazardous area, the charging/data connection must ensure the ratings of protective components are not exceeded. Therefore, the charging connections should either be rated to Um 250 V, or a special charger or cable must be provided.

Note this is only first paragraph of 10.5.3 as the section defining testing is substantial.

Section 7.4.1 contains the following statement:

Where the battery is user-replaceable, the IS mobile device should be marked in accordance with 12.3. External contacts for charging are defined in 7.4.9. Example from certificate showing that the battery has IS parameters.

6.2.2 defines the requirements on plugs & sockets to prevent accidental & unsafe connection errors.

2. Electrostatic discharges are a source of ignition (Some plastics can be statically charged when wiped / cleaned with a cloth). Aluminium can rust becoming a spark risk. SANS/IEC60079-0 section 7 defines the requirements for non-metallic enclosures. Clause 7.4 concentrates on the requirements to prevent electrostatic charges. SANS/IEC60079-0 Section 8 defines requirements for metallic enclosures. 8.2, 8.3, 8.4 defines requirements for Group I, II, III respectively. E.g. Group I limit to 15% aluminium for use in fiery mines.

3. Other than purpose-built accessories (scanners, headsets etc. where the accessory Ui Ii Pi MUST be compatible with the mobile device Uo Io Po), cable connectivity to devices is limited to the Safe Area and these terminals need either electrical or mechanical protection whilst in use in the hazardous area to prevent short circuits / sparks. SANS/IEC60079-11 7.4.9 defines the protection of any connectivity points on the device. The magnetic coupling terminals require IP30 (Group II) (Protected from tools and wires greater than 2.5 millimetres.) or IS limiting circuitry to prevent sparks should they be accidently short circuited.

4. Induced currents from RF. RF power needs to be limited depending on the hazardous area environment. See table 5 (SANS/IEC60079-0) & Table 8 (SANS/IEC60079-14). Whilst Wifi & Bluetooth do not get near the 2W limit, devices can exceed this with GSM & LTE/4G/5G.

Please note that for Group I in South Africa, DMR directives (ME-2-2003 & MS-2-2010) stipulate 500mW maximum power transmission overriding IEC/SANS60079-0 standard of 6W. This is however academic as with no GSM/LTE/4G etc. in an underground mine, mobile devices will only transmit at approximately 100mW (Wifi & Bluetooth).

SANS/IEC60079-0 6.6.2 states that RF power should not be user/software configurable.

5. Product design needs to meet safety component power derating, segregation distances, capacitance & inductance & design to prevent hotspots.

Safety components (resistors, Zener diodes etc.) require 2/3 power derating (SANS/IEC60079-11 7.1). 10.4.2 refers to safety factors (1.5 for Exia & Exib) required.

Requirements for creepage & clearance (including use of encapsulation) for PCB layout (components & tracks) are defined in 5.6.4

7.2 provides details for connectors. Requirements to prevent incorrect connection or interchangeability

7.3 states uses must be rated for the Um voltage and encapsulated (7.3)

CONCLUSION

As can be seen, the requirements to make a device IS are onerous, time consuming & costly requiring specific battery design & PCB component level changes to meet power deratings & creepage & clearance. This makes it very difficult & complicated to convert a standard device to Ex ia/ib. Even Ex ic is challenging.

Supporting Documents:

View PDF Document 

Further related comments:

There are a few practical things to consider when selecting devices:

There have been reports in Europe of fake ATEX certificates & unsafe devices with ‘legitimate’ ATEX certificates in recent months (https://ec.europa.eu/safety-gate-alerts/). The mechanism to remove non-compliant ATEX devices/certificates devices is fractured as it is down to the market surveillance authority in each country. (There is however a formal mechanism for those authorities to collaborate and share information).

1. IECEx has mechanism for devices & certificates to be reported & removed. IECEx also has an online database of certificates, so it is easy to confirm certification & validity.
2. Batteries typically have a limited life (& typically only a 6 month warranty). Devices with replaceable batteries will extend the usable life considerably.
3. MDM compatibility & Android Enterprise compliance provide some guarantee of security & quality.
4. Consider the impact of security with respect to support & bug fixes.

Disclaimer:

The content or information provided in this article is strictly intended for educational purposes and does not constitute a design guide or a Promotional presentation. It is solely meant to provide general information regarding the current standards and an explanation of the reasons behind the high cost of Intrinsically Safe (IS) mobile devices. This article should not be considered a substitute for professional advice, guidance, or instruction. The information presented herein is based on established IS mobile device requirements and standard principles, which may not be universally applicable to all circumstances.

While we strive to provide accurate and up-to-date information, this article is provided for general informational purposes only, to educate the reader and reflects the most current Ex ia/ib and Ex ic standards set out in SANS 60079-11:2012 at the date and time of this article. While we endeavour to ensure its accuracy, we make no representations or warranties of any kind, express or implied, regarding the completeness, accuracy, reliability, suitability, or availability of the information or related excerpts contained in the article, should not be relied upon as the sole basis for making decisions.

The references provided in this article are for illustrative purposes only. They may not represent real-life situations or be exhaustive in their coverage. It is important to adapt and modify the information to suit your specific needs and constraints. The information and practices discussed in this article are intended to stimulate critical thinking and provide a foundation for further exploration. The information provided in this article is not intended to be a substitute for professional advice this article is meant to serve as a general guide and may not encompass all possible scenarios or variations and may vary depending on individual factors.

In no event shall we be liable for any loss or damage, including but not limited to indirect, incidental, consequential, or any other damages arising out of or in connection with the use of this article or the information provided herein. Always exercise caution and use your discretion and due diligence when applying the information provided in this article to your pursuits. We strongly advise you to seek professional advice from Notified Body or Approved Test Laboratory to obtain tailored advice specific to your unique circumstances or alternatively conduct thorough research to supplement and verify the information before making any decisions or taking any actions based on the content of this article. Any reliance you place on the information provided in this article is therefore strictly at your own risk.