It’s not always a simple task to choose a communication solution that will satisfy OSHA or other mandatory or discretionary requirements to provide effective communications in all situations and still be readily accepted by employees. Entrants are often encumbered with equipment such as selfcontained breathing apparatus (SCBA), personal alert and gas detection devices, and safety harness apparatus.

Firefighting is dangerous enough; poor communications in confined space entry can be fatal. Therefore, communication systems utilized should have high intrinsic safety ratings so as to assure safe and effective communications despite the type and/or level of the emergency. This means greater worker safety and reduced employer liability.

In examining the conventional means of communications used, it’s found that many of these have limited application and usefulness. For example, direct voice transmission (talking or shouting), works only in low noise environments and over relatively short distances.

Loud hailers can extend the distance to some degree, may be cumbersome and limited when more than one entrant is involved. Hand signals work in line-of-sight applications and require constant visual contact between communicants. As soon as a back is turned, a vital hand signal will not be seen. Tugging rope will signal the recipient only if the rope is not snagged and conveys only the very basics of intelligence. Electronic communications, which offer better solutions, fall into two main categories, “wireless” and “hard-line.”

Wireless communication devices transmit signals through the air usually via radio frequency waves (i.e. two-way radio)- and provide unhampered mobility to the user. For this reason, it becomes the system of choice for many applications. Radio equipment has its own shortcomings however, making its use limited or even unacceptable in many confined space applications. New solutions may use infrared to link users but these have other limitations without line-of-sight.

Without “line of sight,” communications may become erratic, or worse, entirely missing. Steel, concrete or brick surrounding, or in proximity to the radio, can have a shielding effect. Additional antenna elements installed in strategic locations may alleviate these problems, but this becomes expensive and impractical in portable or emergency applications.

A duplex system has each radio operating on two frequencies simultaneously. In this case, transmit and receive frequencies are open all the time in both directions. Keying the radio to transmit is not necessary as the transmitter is on all the time.This method meets OSHA requirements uses for continuous communication but can use a lot of power and is limited. This is an important factor since most systems are battery operated and should be investigated before making a communication system choice.

If more than two radios are required it becomes necessary to use an additional repeater to accommodate duplex operation. PTT (push-to-talk) or VOX (voice actuated) switches used to switch the radios to transmit are less acceptable since they prevent continuous communications.

Potentially volatile explosive atmospheres will require the use of intrinsically safe equipment. Assembling a multi-radio, intrinsically safe duplex system is an attractive solution only if cost is not a consideration. In summary, although popular for other applications, wireless communications should not necessarily be the system of choice for confined space communications.

Hard-line Communications
In tethered or hard-wired systems, wires are used to interconnect headsets and components to form an intercom between the workers. Advantages of this system outweigh the disadvantages of a physical interconnection between components. Initial and operating cost is low, and non line-of-sight communications is assured. Full duplex lets everyone talk at once, and ensures that no messages are missed. PTT or VOX controls are not required, allowing hands-free operation.

Wired communications can typically be used by up to 10 people. Most systems have immunity from RFI (radio frequency interference), which can be encountered from nearby equipment that generates RF such as arc welders, computers, fluorescent lighting, etc. Wired communications typically do not generate their own RF, and do not cause interference to nearby electronics and other sensitive equipment.

In the event that a confined space rescue becomes necessary, most wired intercom systems can provide the privacy needed to prevent monitoring or interference by those not involved with the operation.

Recently the American Society for Testing and Materials (ASTM) recommended, in summary, that systems: (1) be intrinsically safe; (2) have continuous, hands free voice communications; (3) be dedicated and private; (4) not affect readings of other equipment (i.e. gas detectors); (5) if battery operated, have a low battery warning or backup power; (6) accommodate a minimum of three users; (7) allow for communications between all entrants as well as the attendant; (8) must work in conjunction with any personal protective equipment used, and; (9) must be impervious to the chemicals within the space.

Communication Ropes
Even though training and research into hard-line systems may not be new, Communication Ropes are quite unique. By incorporating communication wires directly into safety ropes you reduce equipment, improving worker efficiency and safety. When considering the benefits of Communication Rope make sure it is high performance and meets OSHA’s requirements, provides a means of rescuing entrants from a confined space and eliminates the need for addition cable.

Poor communications and sub-standard systems, in confined space or rescue situations can be fatal. It is highly recommended that a product or system with the highest intrinsic safety rating be chosen, so that workers, employees and employers are guaranteed that the correct communication components are being used no matter what the emergency. This provides not only the greatest worker safety but also employer liability protection. FSM

Rolf Eberl is president of Special Electronics & Designs Inc. of Kincardine, Ontario, Canada. Mr. Eberl is an Electronics Engineering Technologist and has been involved with SED for 37 years. He was responsible for development of the Rescom Confined Space/Rescue Communications System in 1987 and has more than 20 years experience in the Confined Space Communications field. For more information about this article or topic, you may contact him at rolf.eberl@sed.bz. References: Occupational Safety and Health Administration (OSHA) 29 CFR 1910.146. American Society for Testing and Materials (ASTM) Designation: F 1764-97).