COMMUNICATIONS IN HAZARDOUS ENVIRONMENTS. ATEX radios are essential tools for those working in the oil and gas industry where the working environment may contain potentially explosive gas or dust.
The starting point for all ATEX equipment is the focus on preventing the creation of an ignition source within a potentially explosive environment. Beyond this key point, when designing any two-way communications equipment there are five key considerations: audio performance, coverage, ruggedness, accessories and usability.
The predominant user groups for ATEX radios - from workers in the oil and gas industry, and fire fighters, to airport ground crews and miners - all share challenging operating conditions. They all experience very loud environments, often in excess of 90dB. This drives the most obvious requirement that the two-way radio communications equipment must be able to deliver clear, loud audio which can overcome the background noise.
And here we encounter perhaps one of the toughest technical challenges of communications in an ATEX product. In a non-ATEX product the simple solution is to drive more power into a bigger speaker. Unfortunately to meet the ATEX standards we need to restrict the amount of current which can be used to drive the speakers in the radios and accessories. This in turn directly impacts the loudness and clarity which can be generated. The challenge is to drive the speakers to the loudest, clearest possible level to overcome the 85-90dB ambient noise levels without resulting in the radio becoming an ignition source.
We also find that in certain environments the ambient noise is of a ‘different’ type. The sound of a pump bay on the fire truck is very different to the sound of an airplane engine or a petroleum refinery. The actual noise levels, the loudness, can be very similar, yet the frequencies which are generated can result in very different audio interferences. This requires the radios and accessories to be optimised for each particular type of ambient background noise.
NETWORK AND RADIO COVERAGE
Often the networks in which an ATEX radio is used will be privately owned, by the plant or facility, in which the radios are being used. In the case of civil fire fighters, they will often operate on a regional or nationwide public safety network. In both of these situations, the communications managers will still want to optimise their network to minimise capital investment whilst maximising coverage. This means the transmission power and receiver sensitivity of the radio need to be maximised to give the best possible coverage.
Receiving a signal in the radio does not necessarily cause any major challenges from an ATEX perspective, however when transmitting voice or data from the radio, some of the internal components can generate heat. This in turn can raise the temperature on the outer skin of the radio - and the hotter the surfaces of the radio, the higher the risk of ignition of a gas or dust.
With more efficient RF design, higher transmission power can be achieved without raising the temperature of the radio. The challenge for TETRA has been creating a radio than can transmit at the same power levels as non-ATEX radios. The ETSI standard defines transmit power in “Class” levels – for example a Class 4 radio has a nominal Tx power of 1W, but the actual definition is 30 dBm +/- 2dB, allowing some design flexibility and manufacturing tolerance. For most modern non-ATEX radios the Tx power is aligned to the higher end of this tolerance – i.e. above 1W, however for ATEX radios the actual measured Tx Power of a Class 4 radio is less than 1W – often around 0.7W. This is driven by the need to limit maximum currents in the radio and to limit heating effects.
This obviously impacts the ability for a radio to operate in poor coverage areas of a facility and can result in ‘dead spots’ where communication is lost altogether. Thus the challenge for ATEX radios is how to enable improved coverage through higher transmission power and a more optimised system design, ensuring users are always connected, can hear all messages broadcast and can respond in all emergencies.
RUGGED FOR A TOUGH ENVIRONMENT
Many ATEX environments are found in the extremes of the planet. From the dust and heat of the Middle East, where temperatures regularly exceed 45C, to the cold and wet of Siberia where temperatures can drop below -20C with snow and ice. This drives the need for radios to operate in the most extreme environments, maintaining ATEX performance levels despite exposure to heat shock or extreme cold, as well as dirt, oil, metal dust and chemicals.
We also see ATEX radios deployed by numerous fire services as they will often be required to respond to situations where the risk of exposure to flammable materials and ignition from their equipment is very real. This is further exacerbated by the need to withstand exposure to multiple water sources. This results in the need for equipment to be able to provide multiple levels of IP protection, even after thermal cycling, heat shock and drop testing.
An ATEX radio communications solution does not stop at the radio. There are a wide range of user requirements when it comes to accessories. Most are tailored for use in a particular environment and this has resulted in a wide array of accessories required by the numerous ATEX users: remote speaker mics; skull mics; boom mics; noise cancelling headsets; hardhat solutions; smoke diver face masks; earpieces; and large Push-To-Talk buttons. This drives the requirement for advanced interoperability between multiple types of accessories and the radio itself to satisfy all types of users.
USABILITY AND ERGONOMICS
A significant number of user groups operating in ATEX environments will be wearing gloves and possibly masks, helmets and other protective clothing when using their communications equipment. This means the radio and accessories need to be optimised for use by people who may have reduced tactility in their fingers, possibly restricted vision, and almost without exception, are working in a loud ambient noise environment. This drives design considerations to ensure users can continue to communicate regardless of potentially major restrictions to their normal senses.
A further aspect of usability is the duration of radio use between charges. Some users will be required to operate long distances from a charger or suitable power source and this encourages a need for extended usage time beyond an average shift of eight hours.
These five key requirements demonstrate the extraordinary technical challenges in delivering communications equipment which not only meet end user needs, but also comply with the ATEX and IECEX standards. The MTP850Ex TETRA ATEX radio has demonstrated, time and again, that it meets these extraordinarily tough technical needs with more than 100,000 radios already shipped to customers.
Mark La Pensee, Head of TETRA Subscribers, Product Management
Mark is on LinkedIn at https://uk.linkedin.com/pub/mark-lapensee/0/a13/7b9
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