“The requirements in 30 CFR Part 23 were intended for audible and visual communication devices. However, the concepts of safety and functionality in potentially hazardous atmospheres are also applicable to the communications and tracking equipment required by the MINER Act," the agency said of the impetus for Program Policy Letter (PPL) P08-V-2, adding that it opted to provide "clarifying interpretations" of the criteria for approval as it relates to the MINER Act.
MSHA's Approval and Certification Center in West Virginia has addressed 11 specific guidelines that it takes into account when processing applications from industry suppliers for the approval of communication and tracking systems for use underground.
These include the design of the cables used to connect components, which the agency said must be MSHA-approved as flame-resistant or else enclosed in a hose conduit that is flame-resistant and MSHA-approved.
Also, any device that provides voice, text or signalling and is meant to remain in operation for emergency use, such as a tracking device, will be evaluated under MSHA's existing guidelines for telephones and signalling devices, also known as 30 CFR Part 23.
Should power be lost during an emergency situation, all line-powered devices must have a standby power source so that they can remain operational, the agency said.
That standby requirement is referred to as the 80/10/10 ratio, meaning that it can provide an additional capacity of a recommended 24 hours with 80% idle time, 10% transmit time and 10% receive time.
Also, while a system is working on standby, MSHA A&CC said that its evaluations for approval require that all components be intrinsically safe (IS) by MSHA standards or within an MSHA-certified explosion-proof housing, including interconnecting cables.
With regards to batteries, the agency said that those IS batteries for portable assemblies that cannot be subjected to its "drop test" due to a weight greater than 5kg will be reviewed using its battery enclosure regulations.
For the standby power supplies that involve rechargeable batteries, those units must be designed to mitigate battery off-gassing explosion hazards.
“Examples of available mitigation techniques include venting of the enclosure or automatic de-energisation when an explosive gas concentration reaches 20 percent of the gas’s lower explosive limit," MSHA said in its PPL.
“The standby power source will be subject to MSHA's Criteria for the Evaluation and Test of Intrinsically Safe Apparatus and Associated Apparatus to ensure that it does not create a hazardous condition in the de-energised line power portion of the power supply or in the in-coming line power cable (back-feed protection)."
The centre has also asked that applicants inform it if a submitted system has any potential for radio frequency interference, or RFI, with blasting circuits. A correct application to the agency will include the maximum output power as well as normal operating frequency and the safe distance from blasting circuits on its documentation.
MSHA has also said it considers tracking tags that are worn on a worker's body to be "portable apparatus" and that they will be included in its regulatory drop tests. If the tracking device is an asset tag, or machine mounted, an impact test will be used in lieu.
With regards to lighting, specifically those cap lamps that power communications/tracking components of systems, the lamp units themselves must meet the agency's 19.9(a) performance requirements when both sides are in operation.
“To assure sufficient operational capability in various scenarios, the cap lamp battery should be capable of providing sufficient power to effectively operate the communication and/or tracking component for a period of time beyond the 10-hour minimum," MSHA noted, adding that it recommends an additional four hours of capacity.
Lastly, MSHA said that system approval documentation for lightning arrestors must outline the type used in order to be in compliance with its 57.12069 and 75.521 regulations. This is done to ensure the component does not negate the approval under Part 23, the agency said.
According to the MINER Act, enacted in 2006, emergency response plans are required to outline post-accident communications between underground and surface workers and provide for a wireless two-way medium to do such within three years.
It also outlines the requirement for electronic tracking systems that allow surface personnel to locate underground workers, particularly when trapped below the surface.
A full copy of the PPL can be found at MSHA's website.
