Designing communications equipment for hazardous environments
18 September 2015
The scale of modern production means that a wide range of industries generate dangerous working environments where correct controls and safety must be stringently applied. In this article, Mark La Pensee of Motorola Solutions looks at the main considerations for providers of communications equipment for use in these hazardous environments, which not only need to meet end user needs, but also comply with different national standards.
From the fuel in our cars to the food on our plates, we give very little thought to how complicated, difficult or even dangerous the processes might be behind our daily necessities. The reality is that many of the goods we regularly use will have passed through a hazardous environment during their creation and this presents a considerable communications challenge for those securing raw materials and manufacturing products.
Understanding what constitutes a ‘hazardous environment’ is a critical consideration when meeting communications and operational requirements. An environment is defined as potentially hazardous if three conditions are met: there is a fuel source - a gas, a vapour, or some sort of ignitable dust; oxygen; and an ignition source. Many industrial facilities encompass large, complex environments and these require integrated communication systems to facilitate effective and safe operations. Hazardous environments demand highly reliable, easy to use and intrinsically safe communication equipment.
Used in a wide variety of electrical equipment, intrinsic safety is a protection technique that focuses on allowing safe operation by preventing the creation of an accidental ignition source in the presence of oxygen and a fuel.
Radios conforming with ATEX and IECEx standards are prime examples of intrinsically safe communication devices that are designed and optimised to meet challenging demands.
When designing an ATEX two-way radio system there are five key considerations: audio performance, coverage, ruggedness, accessories and usability. In conjunction with the intrinsic safety capabilities, it is vital to address these considerations to establish usability. Invariably, hazardous environments are loud, dirty, hostile places and these conditions will tend to define the uniqueness of an ATEX communications device.
For the predominant user groups - firefighters to oil and gas, chemical, heavy industry, sea port, airport and mine workers - all are different in their deliverables to the market, yet share common environmental operating conditions. Invariably they are all constantly very loud environments, usually in excess of 90dB, which is deemed harmful to hearing. The most obvious requirements are that the two-way radio communications equipment be able to operate with clear audio which can overcome the background noise and be sufficiently rugged to withstand daily exposure to all types of dirt and dust. But the equipment must do all this whilst not providing any ignition source to the hazardous environment.
And here we encounter perhaps one of the toughest technical challenges of communications in an ATEX product. The ATEX standards 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, all 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 will be very different to the sound of a steel plant. 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 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 firefighters, 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.
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 of the outer skin of the radio, and the hotter the skin, the higher the risk of ignition of gas or a dust.
With more efficient radio frequency (RF) design, higher transmission power can be achieved without creating an ignition source. The ETSI standard allows manufacturers to declare their transmission class with a +/- 2dB tolerance. While all manufacturers declare they are Class 4 (1W), when their transmit (TX) power is measured we see it is actually closer to 0.7W. 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. This is why higher transmission power and a more optimised system design is necessary to provide maximum coverage, ensuring users are always connected, and can hear all messages broadcast and respond in all emergencies.
The ATEX environment
Globally the majority of ATEX environments are also found in the extremes, from the heart of the Middle East, where temperatures regularly exceed 45C and are extremely dusty, to 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, dirt, oil, metal dust or chemicals.
For the numerous fire services that deploy ATEX radios 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 jets and fire hoses. The result is the need for equipment 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 a radio. There is 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 an 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 across multiple types of accessories and the radio 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.
About the author:
Mark La Pensee has been Head of TETRA Subscribers Product Management at Motorola Solutions since 2011. Previously he held a number of senior project management positions at Nokia, where he worked for more than 12 years, and spent three years as an electronics engineer at Matra Marconi Space Systems.