This made them an astute long-term purchase, said David Reed, managing director of safety equipment supplier OTB.
Duplex radio systems allowed the receiver and sender to speak simultaneously, unlike simplex radios, where only one person at a time could speak.
"In communications, a common misunderstanding is in the description of simplex radio communications as two-way," Reed said.
"They are two-way in the sense that communication is possible back-and-forth between the entrant and attendant, but only with one person talking at once."
Reed said time lost from miscommunication could prove fatal during rescue operations.
"Tragic situations can happen in seconds or fractions of seconds," he said.
"Workers and rescuers going into confined spaces are often faced with limited/restricted entry, difficulties with communication, dangerous atmospheric conditions, lack of oxygen and the presence of toxic or flammable gas.
"A crucial safety question is how can we stay in touch with the entrant every second – and I mean every second."
Duplex systems were hands-free, static-free and water proof, said Reed. They were not affected by interference, had a minimum battery life of 200 hours and were sturdier than most simplex units.
"These are enormous benefits that often go unsung," Reed said.
"They should be considered an investment in efficiency and safety equipment, rather than another cost."
Con-Space Confined Space communications system the CSI-2000 Hardline is Mine Safety & Health Administration (MSHA) approved for use in underground mining, approval No 9B-199-0, meeting North American/International standard.