U.S. Department of Labor

Mine Safety and Health Administration 1100 Wilson Boulevard Arlington, Virginia 22209-3939

ISSUE DATE: FEBRUARY 25, 2003

PROGRAM INFORMATION BULLETIN NO. P03-3

FROM:           MARK E. SKILES  
                       Director of Technical Support

                        RAY McKINNEY  
                        Administrator for
                             Coal Mine Safety and Health

                        ROBERT M. FRIEND  
                        Administrator for
                             Metal and Nonmetal Mine Safety and Health

SUBJECT:     Recommended Design Safeguards for Permissible Remote Controlled Continuous
                        Mining Machines

Who needs to have this information?
Operators of underground coal or gassy metal and nonmetal mines, manufacturers of remote controllers and remote controlled continuous mining machines, Mine Safety and Health Administration (MSHA) enforcement personnel, miners' representatives, state mining agencies, and other interested parties need this information.

What equipment is affected by this bulletin?
This Program Information Bulletin (PIB) applies to new designs of permissible remote controlled continuous mining machines approved under Title 30 of the Code of Federal Regulations (30 CFR), Part 18 and to existing approved equipment in use in the mines as well. It applies to remote controllers that are portable and hand carried, or worn on the operator's body, to remotely control continuous mining machines from a location off the machine but in close proximity to and in visual and audible range of the machine being controlled. It is applicable to remote control systems using radio, infra-red or direct tethered electrical connection methods.

What is the purpose of this bulletin?
The purpose of this bulletin is to inform the mining industry of recommended safety design features for remote controlled continuous mining machines. These recommendations could help reduce the number of accidents resulting from the use of such equipment. This bulletin recommends safety design features for the following functions:

(1) Remote Emergency Stop Devices, located on remote controllers, that initiate an emergency shutdown function on remote controlled continuous mining machines;
(2) Prevention of accidental activation of machine tramming functions; and
(3) Reduction of the machine slew rate when the tram controls are split or singularly activated.

What is the background for this bulletin?
A review of thirteen fatal accidents involving the use of remote controlled continuous mining machines since 1988 reveals that two of these accidents were associated with the accessibility of the remote emergency stop device. Three accidents involved the bypassing of mechanical interlock safety devices on tram controls and eight accidents involved accidental activation of the tram controls.

     Concerns With the Design of Remote Emergency Stop Devices
In one accident, a remote controlled continuous mining machine operator was fatally injured when he was crushed between the continuous mining machine and coal rib. The remote controller did not have an emergency stop device that was readily accessible in the event of an emergency. In another accident, a maintenance helper sustained fatal crushing injuries when he became trapped between the conveyor boom and the mine roof. The chain conveyor became activated due to an electrical short inside the remote controller. The availability of a readily accessible emergency stop device may have saved the victim's life.

Good ergonomic design for a remote emergency stop device allows the device to be quickly and easily activated in an emergency. The device should be readily accessible, prominently located, and clearly differentiated from other controls. Existing emergency stop devices do not consistently utilize these design features, and as a result, confusion and delays in activating the device in an emergency situation can occur.

     Concerns With Bypassing Mechanical Interlock Safety Devices on Tram Controls
There have been three fatal "caught-between" type accidents where the mechanical interlocks on the remote controller tram controls were defeated by the use of tape, thereby bypassing protection against accidental activation. Taping the interlocks was identified as a contributing factor to all three accidents.

PIBs P97-31, P98-19, and P00-14 were issued to emphasize the importance of the mechanical interlocks and warn of the safety hazards associated with bypassing this safety feature. The use of same-hand activated mechanical release devices on tram controls proved to be inconvenient and difficult to operate over a working shift and are often bypassed by machine operators. These devices have not proven to be an effective means for preventing accidental activation.

     Concerns With Accidental Tram Control Activation
A review of accident data identified eight reported accidents (fatal or nonfatal) involving accidental tram control activation on remote controlled continuous mining machines. Of these eight accidents, four (including one fatal) have been attributed to a cable falling across the remote controller while it was left unattended, causing the tram controls to be activated. The other four were attributed to unintentional body contact. The need to prevent accidental tram control activation is recognized and has been addressed in most designs. However, all designs should incorporate these safety features to prevent accidental activation of the tram controls. Accident analysis has also identified the need for limiting the maximum slew rate of the machine under tram control settings that produce a pivoting action of the machine. Limiting the slew rate under these conditions has the potential to reduce pinning hazards to operators unintentionally positioned at machine pinch points.

What is being recommended through this bulletin?
MSHA recommends certain design safeguards and training:

I. Design Safeguards
Equipment manufacturers should implement the design safeguards in all new designs. MSHA also recommends that manufacturers of existing approved remote controllers and remote controlled continuous mining machines currently in use modify their equipment, to the extent possible, to include the recommended safeguards. Design changes should be submitted for MSHA approval under 30 CFR, Part 18. Field testing of remote controlled equipment is recommended before a design is finalized and submitted for approval. MSHA's Experimental Permit Program may be used to allow field testing.

MSHA recommends that the following design features be addressed:

Remote Emergency Stop Device
The remote controller should be equipped with a remote emergency stop device that: (1) Overrides all other machine controls; (2) Removes power from machine movement actuators; and (3) Causes all moving parts to stop within the shortest possible time. Resetting of remote emergency stop devices requiring manual reset, or release of momentary action remote emergency stop devices, should not cause any function of the machine to operate. In mines utilizing extended cuts, the emergency stop device should cause the circuit breaker at the power center to trip rather than the onboard machine circuit breaker, if a circuit breaker is used for removing power from machine movement actuators.

The remote emergency stop device should be:
(1) Differentiated from other controls by size (larger) or shape;
(2) Located in a readily accessible, prominent location in the operator's direct field of vision on the remote controller's main control panel;
(3) Colored red;
(4) Activated by a pushing action perpendicular to the controller's main control panel surface. Note: For example, a red, mushroom-head shaped switch actuator, may be used for this purpose, but other designs meeting the general recommendation could be used.

The remote emergency stop device should be clearly labeled "Emergency Stop," and should be protected against the entry or buildup of coal, dust, or other foreign material that could hinder or block its activation. Ready access to the remote emergency stop device should not be hindered by the proximity of other controls or by mechanical guards. The design should consider the need for additional spacing when gloves are worn.

Operation of the remote emergency stop device should be tested during the machine pre-operational checks.

Accidental Tram Activation Protection
All control devices, such as buttons, levers and joysticks, used for controlling the tramming function of remote controlled machinery, should be designed such that the tramming function stops when the device is released. The remote controller actuating controls for the machine tram function should be designed to reduce the likelihood of unintentional activation. Tramming functions can be activated when cables or other material fall on the controls, or with unintentional hand or body contact. Recessed selector switches, shrouded selector switches, deadman control, two-hand control, or sequential two-switch operation such as use of a tram function enable switch should be used. These safety features should be ergonomically designed, tamper-resistant, and not interfere with the normal operation of the mining equipment.

When sequential two-switch operation (tram enable switch) is used, a tram function inactivity timer should be provided to disable the tram function if the tram controls are not activated within a pre-programmed time period. The tram function inactivity timer should be set as low as reasonably practicable, consistent with convenient machine operation. Five seconds is the recommended maximum inactivity timer setting.

The controls actuating the machine tramming function should be protected against the entry or buildup of coal, dust, or other foreign material that could hinder or block their activation or movement. Note: The use of rubber boots or other effective means could be used for this purpose.

The use of same-hand activated mechanical release devices on tram controls, such as lift-to-operate mechanical interlocks on tram control levers, should be eliminated. Note: Safeguarding devices that impede convenient operation and that prove to be tiring over a working shift are often bypassed by operators.

The use of a "global" guarding method, such as a raised guard rail surrounding all the switches on the control panel, is not a recommended method for preventing accidental tram control activation when used as the only prevention method. Note: This guarding method does not provide adequate protection against accidental activation by cables of various sizes or other foreign objects and may result in accidental control activation when using the guardrail as a carrying handle. Attention must be paid in the design to ensure that the use of any mechanical guarding methods does not hinder activation of the remote emergency stop device.

Machine Slew Rate Control
Remote controlled machinery utilizing a machine tramming function should be equipped with control circuits that reduce the machine rotational slew rate when the tram controls are set with one control forward and one control reverse (split cat) or a single control forward or reverse (hard turn) position. When the tram controls are split or set in a hard turn position, the tram speed of the activated drive(s) should be limited to no greater than the slowest operational tram speed provided on the machine, in order to minimize the slew rate (rotational speed) of the machine.

The slew rate of the machine needs to be minimized to obtain a pivoting action of the machine that reduces potential "caught-between" type hazards to machine operators inadvertently positioned at machine pinch points.