USING WIRELESS TECHNOLOGY TO INTEGRATE GAS DETECTION AND WORKER SAFETY


Communication is vital when dealing with atmospheric hazards. It’s not enough to measure the hazards; procedures need to communicate the results in real time to affected workers, managers and emergency responders.


The methods used to communicate monitoring results are a central part of any atmospheric monitoring program. After all, the accidental release or accumulation of toxic or combustible vapors is one of the most signifi cant threats to worker safety. The faster the existence of a dangerous condition is discovered and communicated to workers, supervisors and emergency responders, the less likelihood there is for property damage, injury or loss of life. When the location of the gas detector is distant from the emergency responders, timely communication of this information is even more critical.


The methods for acquiring and disseminating this information are changing very rapidly. In the past, emergency conditions were communicated by means of a separate hand held radio, telephone, pager, siren or horn. Advances in wireless technology are making it possible to transmit information in real time between individual workers, supervisors and emergency response team members. This is particularly important for solo workers, workers in confi ned spaces, and workers performing other risk associated tasks. Supervisors are never out of contact, even when workers are out of sight. Besides being able to see readings in real time, wireless connection allows two way communication between supervisors and instrument users. The central idea is to make the monitoring results immediately available to whoever needs the information exactly where it is needed. Results can be displayed locally on a tablet, laptop, cell phone, or personal computer, transmitted to a standby rescue team, or redundantly displayed on a PLC as part of the site’s environmental health and safety system. Alternatively, multiple instruments can be linked into self-contained networks controlled and integrated by means of a mobile wireless host.


In the past, the most common method for real-time communication of readings and / or alarm state information has been by means of hard-wired connection between the gas detector and a controller or PLC located in a central safety offi ce, guard shack or control room. This approach is still commonly used with permanently installed “fi xed” gas detection systems. Using a cable to connect portable instruments to a nearby controller is more challenging. Some designs allow multiple instruments to be connected by means of cables to form a multi-monitor system. This approach has several potential drawbacks. The length of the connector cable is often limited, the sensors provide readings for the general area as opposed to readings from the breathing zone of individual workers, using multiple instruments linked by connector cables can be cumbersome, and as requirements have become more rigorous, the certifi cations carried by these products


are often not be as desirable as the certifi cations carried by non- cable connected portable instruments.


Connecting instruments with a remote host or terminal by means of wireless or Radio Frequency (RF) links has long been an attractive alternative. However, licensing issues, limitations on the number of transmitters able to share the available frequencies, and concerns about the dependability and robustness of the wireless link left many site managers unwilling to take a chance on this otherwise attractive technology. Over the last few years, however, changes in RF transmission technology have made wireless integration of monitoring systems increasingly commonplace. This trend continues to gain momentum, as more and more monitoring and control systems offer safety managers the option to “go wireless”. In addition, the nature of the transmitted information has become increasingly sophisticated. Readings, alarms, time history exposure calculations, “man down” alarms, communication link status and strength, and two way communication between the instruments and the server are all now available in real-time via wireless link.


As monitoring programs become more dependent on telemetered information to verify worker safety, the integrity of the real-time communication link becomes increasingly important. The emergence of new types of digital radio communication methods, greater fl exibility in positioning system elements to maintain communication in complicated monitoring environments, and the ability of the system itself to constantly assess the status and communication linkage between system elements, have signifi cantly increased the reliability and feasibility of using wirelessly transmitted information in health and safety monitoring programs.


• Methods for Wirelessly Communicating Gas Detection System Information


There are two basic approaches currently being utilized for wirelessly transmitting information between portable gas detectors, and a remotely located base station or information processing point. The fi rst is interfacing the instrument with an add-on wireless communication module. One method is to use a Bluetooth®


transceiver built into the instrument to provide


a wireless link over a limited distance between the instrument and a “smart” cellular telephone, laptop or tablet. The smart phone or tablet is used to communicate via cellular telephone or WIFI Internet connection with the information processing point or terminal. One of the limitations of this approach is that


when the instrument is being used in a hazardous location, such as a confi ned space, the device used to send the information onwards must be certifi ed for use in the same hazardous location as the instrument. Intrinsically safe cell phones and tablets are available, but can be very expensive! Another problem is that cellular telephone and WIFI connections do not work very well in confi ned spaces and other industrial environments where walls, heavy structures and equipment block the transmission.


A variation of this approach is to embed the cellular communication module within the instrument. This avoids the issue of needing a secondary cellular communication device, but does not solve the problem structures or conditions that block the transmission. The work-around for this limitation is to add repeaters which rebroadcast the information, usually at greater intensity, over a greater distance, or through the intervening structure. The second approach is to include an integral RF (radio frequency) modem inside the instrument.


Several related technological trends and advances have made using real-time RF data transmission increasingly attractive. A major factor is the availability of “ISM” (industrial / scientifi c / medical) radio transmission frequencies that in many jurisdictions do not require a user license for transmission. Although local or national regulations vary, in many parts of the world users can simply purchase instruments that include integral ISM band RF transmitters, and put them into service without the need to obtain a radio license. In other jurisdictions, a license is required, just as a license is required for other types of hand held RF communication devices and radios.


Another factor is the increasingly sophisticated methods used for radio transmission and signal processing that make it possible to maintain a solid communication link between the instrument and the remotely located base controller. Encrypted, frequency hopping digital transmitters are now routinely used to protect the real-time digital RF data stream signal from interference from other RF sources. This technology additionally helps ensure that the communication link is secure and robust enough to be dependable for use in safety monitoring programs.


Spread-spectrum, frequency hopping radio transmitters send a short, high-speed stream of digital packets of information at one frequency, then “hop” to another frequency to transmit the next stream of data packets. Part of the information encoded in the string of packets is the frequency where the receiver (or transceiver) should look for the next string. Because of heavy redundancies


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