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Intrinsically safe handsets

Date: 19th March 2013
Topic: Looking At
Technology: Digital PMR, Wi-Fi
Manufacturer: Airbus Defence and Space, Sepura

34_Looking_At_edited.jpgFirst responders in fire and rescue services, as well as private business users in offshore/onshore oil and gas, petrochemical, food processing and other activities, may find themselves frequently confronted by potentially explosive atmospheres in their workplace. These may be due to the presence of flammable gases, mists, vapours or combustible dusts.

When air is mixed with these in the right proportions, all that is needed to create an explosion is an ignition source. Such a scenario might easily exist in the petrochemical industry, or where there are fine organic dusts such as grain flour or wood, as well as in activities such as paint spraying at a local vehicle body repair shop.

Reducing the risk of an explosion in such an environment is best done by preventing dangerous substance release in the first place, or eliminating the chance of an ignition source being added to the mix. Part of that process is ensuring that correct equipment is used wherever and whenever possible.  While ATEX requirements cover all industry sectors, equipment makers, etc, in the case of radio end users that means operating handsets which meet ATEX standards.

Regulations, directives

Many countries have national law governing hazardous working environments. In the UK, for example, a duty of care is placed upon employers to eliminate or control explosive atmospheres in the workplace by the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR). These define an explosive atmosphere as a mixture of dangerous substances with air, under atmospheric conditions (20°C to 40°C and 0.8 to 1.1 bar of pressure), in the form of gases, vapours, mist or dust in which, when ignition occurs, combustion spreads rapidly to the entire unburned mixture.

These regulations place the onus on any organisation whose staff may face such a scenario to ensure that they are appropriately equipped.

In the European Union, two crucial European Directives, known as ATEX (‘EXplosive ATmospheres’) directives, are aimed at regulating the control of those explosive atmospheres: Directive 99/92/EC (also known as ‘ATEX 137’ or the ‘ATEX Workplace Directive’) relating to minimum requirements for ensuring the health and safety of workers at risk from explosive atmospheres, and Directive 94/9/EC (also known as ‘ATEX 95’ or ‘the ATEX Equipment Directive’) concerning electrical equipment and protective systems intended for use in potentially explosive atmospheres. 

These help identify areas where explosive atmospheres might exist, enabling employers or organisations to classify them into zones based on size, location, and likelihood of an explosive atmosphere occurring in that zone. Such a zone might be physically marked on site with ‘EX’ signage. Individual devices such as radios are marked with codes indicating the zones or hazards they are certified for.

This is where several of today’s handset manufacturers have stepped in to address the needs of those radio users who face such hazards in their work. Designed to meet essential health and safety requirements, these handsets undergo strict conformity procedures often involving third-party testing and certification, in turn leading to the handsets being classified with the letters ‘EX’.

At the current time, the manufacture of Intrinsically Safe (IS) handsets is particularly prevalent in the Tetra community.

One such manufacturer, Sepura, launched the STP8X series in 2011, extended the company’s reach into hazardous gases and dusty environments, where Intrinsically Safe ATEX/IECEx certified devices are an essential requirement.

Mark Barnby, product manager, said that the STP8X meets the most recent updates of the ATEX and IECEx standards. He emphasized that the company had paid attention to how real users around the world operated their Intrinsically-Safe radios and accessories in a wide variety of market segments. “Loud, clear audio, the ability to use the radio whilst wearing bulky gloves and a new level of ruggedness were all key attributes that were not yet present in the market”, he said.

Manufacturing process

While the basic functionality of ordinary handsets and ATEX radios is the same, the key differentiator is the actual manufacturing process,  Mr Barnby explained. Additional safeguards are put in place in the ATEX process so that the radio remains ‘safe’ even under fault conditions. Should a fault occur, sparking cannot start a fire.

Another early Tetra ATEX player was Cassidian, which launched its first such product, then known as the Nokia THR880i Ex handportable, back in 2007. At the end of 2010 the company’s THR9 Ex was released. Pierre Lopez, head of terminal and indirect channel business at Cassidian, said: “With ATEX and IECEx certification for both gas and dust, the THR9 Ex offers protection against physical and environmental exposure in explosion-prone areas and can be used where flammable substances are produced, processed, transported or stored, such as oil and gas, petrochemical and steel industries as well as rigs, airports and harbours, and it also meets the needs of fire brigades for Ex equipment when working in hazardous scenarios.”

The ATEX manufacturing process follows stringent rules under the strict supervision of an independent ‘Notified Body’. Mr Lopez continued: “Generally the electronic board is compounded to avoid any spark or overheating in contact with gas. Component reliability and traceability at each level of the manufacturing process is key to ensure the high quality of such safety devices.”

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