Mobile Devices in Hazardous Areas

One of the most common items we get asked for is an ‘intrinsically safe phone case’, or asked to explain why a waterproof case can't ensure that their iPhone or iPad is safe to be used in a Zone 1 area - after all, "if it's water proof, it must be gas proof as well - right"?

There is no doubt that we need technology in the workplace, but when it comes to mobile devices sych as smartphones and tablets, the easiset methods of rendering electrical items safe in potentially explosive environments, aren't all that easy. Placing your iPhone in a flameproof case really does mess with several aspects of usability. This Tek-Tip is therefore provided to assist those looking to integrate mobile devices into hazardous areas, while debunking a number of myths that prevail, and are even openly marketed on the internet, and which can be huge pitfalls in the journey to making an accurately informed decision.

Let's explore some of the most common questions:

• The ‘intrinsically safe case’ for my Apple™ or Samsung™ device.
• The water proof case: if the gas / dust can't get in, it's safe... right?
• I've seen an ex-certified item on an overseas website; can I use it here in Australia?
• Can you tell me which level of safety (or zone) I need?

Before we go on, a few disclaimers about the material provided:

This page is intended to provide general information only, and is not in any way specific to particular situations or circumstances. You should always consult with and follow the regulations of your workplace under the guidance of a suitably qualified and endorsed hazardous area assessor or compliance officer before using any electrical equipment in a potentially hazardous area.

Secondly, this is not meant to be an engineering discussion paper. If you're looking for a guide to the standards and principles behind hazardous area certification in general, you may wish to take a look at our separate Tek-Tip on Hazardous Area Certification. Should you find any errors or omissions with this document, please notify us, and we will do our best to include your suggestions where relevant.

With that said, if you're the cheating kind, or don't want the detail, you can skip to the end and get the answers to the questions. If not, please read on...

Dealing with the issues...

Stop them at the gate: In many cases, the issue of allowing mobile devices in ex areas is simply one for the 'too-hard' basket, and policies reflect this either by not allowing them on site or ignoring the issue entirely. While restricting mobile devices entirely may have been accepted practice a number of years ago, business demands for efficiency and productivity mean that any plant manager trying to legitimize this as an acceptable policy clearly have their head in the sand. The latter is an invitation for a lawsuit!

Having realised the need, what generally follows is a consideration of multiple pathways dependent on the risks, challenges and requirements of the particular site.

Defining the need: The needs of an industrial field based worker are clearly different to those of an office worker or consumer. Devices must be able to withstand high impact, impervious to dust and liquids, with expectation of an IP67/8 (submersible) rating. Inevitably, there are differing strategies for accommodating these needs, which loosely take the form of 2 options:

• Rugged or consumer devices - in a flameproof case;
• Purpose built, certified devices;

It is in this area of exacting standards and requirements that confusion so easily exists, and the devil is certainly in the detail...

The Devilish Details

There have undoubtedly been some huge advances in technology recently, allowing today's smartphones and tablets to have the computing power of PC's or laptops. Thinner and lighter screens, more efficient processors, and better battery options have encouraged manufacturers of military grade rugged devices to look at ways to leverage these advances to manufacture hazardous area certified products. A few have succeeded, and many have failed, having not realised the very stringent requirements and testing of devices that is mandated in order for ex certification. Others have made it past this step, only to be confronted by the ultimate test, the client's ability to use it. After all, there is no purpose in developing a device that is expected to be mobile, but you need a porter's trolley to shift it!

Regardless of the manufacturer, in order to make a device 'safe' the manufacturer is going to have to follow one of the approved 'Protection Concepts' which can be used to meet the standards. Many of the concepts normally used for motors and heavy machinery items obviously wouldn't suit mobile devices, like drowning them in oil or encasing them in steel. This leaves three methods that are employed, each with their own advantages and disadvantages:

Flameproof Enclosure (Ex d)

Using this concept, the device is placed in an enclosure that is designed to withstand the force of any internal explosive event, and vent the energy or 'flame' through pathways that are so small, that it cannot reach the potentially flammable atmosphere around it. This is the system typically employed by the manufacturers of the incorrectly named 'Intrinsically safe' cases.

Pro's:

It's a relatively easy solution to manufacture and the case can form part of the rugged protection required to meet the standards. Repairs can be completed relatively easily as the case can be removed by a suitably qualified person, and then replaced after the repair event.

Con's:

Consumer devices are made to dissipate heat through the case using the ambient air around them. Enclosing the device in a case with minimal ventilation is hardly part of the manufacturers recommendations and could well void any warranty. Unless your device is designed to be charged wirelessly, opening the case to access the charge port involves breaching the flameproof case - something that should only be done by a suitably qualified person. This wouldn't be accepted on site, so you have to question the rationale for doing it daily to charge your mobile device. The case around the existing device inevitably leads to increased weight and size.

Powder filling (Ex p)

Using this concept, the device is placed on a shaker table and very fine powder is inserted into the device so that all components are essentially 'drowned' in dust to the point that no air can enter the unit, rendering it impossible for a fault to result in an ignition of the potentially flammable atmosphere around it.

Pro's:

Provided the standard rugged device is suitable, there is no requirement for internal device or circuit modifications.

Con's:

The device must be intact at all times, as even the slightest leak of powder allows air into the unit rendering it unsafe. Inspections of operational devices must therefore be extremely vigilant. Repair timeframes can easily blow out, as in addition to the actual repair time, all of the dust must be removed from the device and then reinserted after the repair event, often causing delays of days, rather than hours due to this process. Chaffing of minute SMT components which were not manufactured to be surrounded by powder is an issue, unless they can be suitably protected. Weight of the item is increased due to the added powder.

Intrinsic Safety (Ex i)

Using this concept, the currents and voltages used and stored within the device are highly regulated to the point at which there is insufficient energy to cause an ignition of any external gas or dust within the limitations to which the device is certified. Different classes of intrinsic safety specify the types of hazardous gases or dust atmospheres in which the equipment can be used.

Pro's:	All device modifications are internal, so if the ex unit is based on an existing commercial or rugged device, the size and weight variations are limited to the requirements to withstand the required physical testing. Battery life is exceptional due to the nature of the protection concept.
Con's:	Large display screens or hungry processors may be difficult if not impossible to incorporate due to the current limitations. Specialist circuits must be employed to safeguard the device from any external electrical event when charging. Cooling fans or any similar motor cannot be used.

Figuring out which concept has been applied to the device you are considering involves looking at the certificate, which will commonly state the protection concept used. If not, then the labelling on the device will show you. For an explanation of the labelling and what it means, see our general Hazardous Area Tek-Tip.

The pedigree of the manufacturer and certifying body:

While this isn't generally an oversight when commercial IT decisions are made for rugged or business machines, it's surprising how often ex devices are purchased on specification or compliance requirements alone, without any thought for the quality of the underlying device. This is especially the case, if the device has been purpose built by a relatively new manufacturer. Ask yourself:

• How long has the company been manufacturing ex devices?
• Where was it certified - is the ex certificate from a reputable test house, and do I trust the country of origin?

Just as there are in the commercial world there are brands you'd rather avoid, the same applies to products from manufacturer's that come and go, or test houses in countries where standards aren't as vigilant. There's been more than one case of a certificate having been withdrawn for an ex device, leaving the customer unable to use the device in any ex area.

The reality of use:

Producing portable devices for Zone 0 applications is extremely difficult and the need for workers to operate in these dangerous conditions is generally kept to an absolute minimum for obvious reasons. Areas where potentially explosive liquids, gases or dust are being produced, refined or where some repeated contact is likely are generally classified as Zone 1. Conversely, examples of Zone 2 areas are storage areas, maintenance workshops and other ancilliary areas adjacent to the main production areas.

When considering portable mobile devices in these areas, the likely hood of their increased use in instances of emergency must be taken into consideration, as a Zone 2 area potentially becomes Zone 0 very quickly! Particular attention and training needs to be made to this aspect of the actual use of certain mobile devices such as phones or tablets, and their potential for use in such scenarios.

Hopefully the above has been helpful in answering some of your questions in this area. If you've read all the way through, you should already know the answers to the questions at the top of the page, however if you've cheated and pressed the link, here are our answers to those questions:

• The 'intrinsically safe' case - does it really exist?
  

  NO As you would have seen above, intrinsic safety is about limiting the currents within the device so that it is incapable of holding or generating sufficient energy to cause an explosive event to occur. The case you are considering is flameproof (exd), which if you think about it long enough, raises two issues:
  1) Was my consumer or ruggedized device designed to be put inside a case with limited air to cool it?
  2) How do I ensure the flameproof case stays intact if I'm opening it every day to charge my device?

  Unless the mobile device has been manufactured, or re-manufactured to exist within the confines of a case, and can be charged without opening that case, putting devices in flameproof cases is inherently a bad idea.