Technology News

No. 455 May 1997

U.S. Department of Health and Human Services

Public Health Service

Centers for Disease Control and Prevention

National Institute for Occupational Safety and Health

Roof Hazard Alert Modules

Objective

To discourage miners from going inby unsupported mine roof by

developing intrinsically safe devices that render the attendant hazard

more evident, direct a person's attention to read the warning message on

the module, and thus avoid the hazard beyond the device.

Background

Some miners unknowingly venture beyond the last row of roof bolts

in an underground coal mine. The new permissible-type, intrinsically

safe design modules described here represent an engineering intervention

strategy toward improving miners’ ability to recognize and avoid the

hazardous zone of unsupported mine roof. 

These devices are designed to improve the miner’s recognition of the

unsupported roof by marking the end of roof support with a flashing red

light and a written message warning miners to avoid the unsupported area

ahead.

How It Works

Two different types of battery-powered roof hazard alert modules

(RHAM's) have been designed, fabricated, and initially evaluated at our

facilities. One type of module features a rechargeable cap lamp

battery for its energy source; the other type uses disposable 9-V

alkaline batteries.

 As shown in figure 1, the rechargeable RHAM was fabricated from

a conventional 4-V cap lamp battery unit. A special in-house circuit

interrupts the conventional incandescent bulb to flash through a red lens

at about 3 Hz. The basic part of the prototype unit is a commercially

available cap lamp with remote control adapter powered by a 4-V, twocell, lead-acid battery.

The new features added by NIOSH Pittsburgh Research Center

(PRC) personnel include (1) a solid-state timing circuit and threeposition mode switch that are situated within the existing remote

adapter and battery cover case, (2) a metal bracket and hook assembly

to coil the cable, attach the lamp to the bracket, and suspend the entire

unit from a mine roof bolt plate eyelet, (3) a red lens, (4) a warning

decal affixed below the lamp, and (5) a mode switch decal.

The added electrical circuit is of low power and energy storage

design and is ultimately expected to be amenable to an MSHA-certified,

intrinsically safe design for operation inby the last open crosscut in a

gassy mine. PRC personnel plan to apply for an experimental permit

for this device and others described below, which will signify an

intrinsically safe design.

At an underground coal mine, one or more of these RHAM's would

be removed from the battery-charging station aboveground and the new

three-position switch moved from the "CHARGE" to the "OFF" mode.

The unit(s) would be carried by someone to a mine transport vehicle and

later to the underground working area. At those places underground

where mining has progressed beyond 4 ft of the last row of roof bolts, one

o f the new RHAM units i s

suspended from a roof plate eyelet within the last row of roof bolts and

rotated so that the lamp is facing outby. The unit hangs down from the

mine roof about 1 ft, which allows for most personnel and equipment

movements underneath in high coal seams, but would restrict equipment

movements in lower seams. In lower seams, the compact RHAM

(figure 2) is recommended instead.

Once the high-coal RHAM is in place, suspended from the roof bolt

plate eyelet, it is activated into a flashing mode as follows: (1) the

common three-position lamp switch is selected for the forward ( )

arrow and (2) the new three-position toggle switch (located atop the

battery cover case) is selected for the "FLASH" mode. With both
Figure 1.—Rechargeable

roof hazard alert module (4-V).

Figure 2.—Disposable magnetic-mount roof hazard alert

module (9-V).

switches set as above, the unit will then be activated and produce a 3-Hz

(approximately three flash bursts/second cycle) red flashing light. This

bright red flashing light should provide ample warning to mine

personnel and visitors of the unsupported mine roof area hazard just

ahead. Because the duty cycle of the RHAM light unit is

approximately half-on and half-off, it is expected that the unit will

consume much less energy and last for more than a shift of operation

(>10 h). In practice, the RHAM could be left on until the hazardous

roof area is bolted or replaced with a recharged unit.

Similarly, the low-coal RHAM unit shown in figure 2 was designed

to be used in thinner seams and features a much shorter profile and

compact package. Two different types of this design were fabricated;

one featured a hook mount similar to the high-coal version shown in

figure 1, whereas the other, shown in figure 2, features an internal

magnetic mount that minimizes the projection down below the mine

roof bolt (the extension below the roof bolt head is about 2 in). The

prototype units were fabricated from machined aluminum stock, but

other types of case material are possible. These units are constructed to

be dust- and water-resistant and should withstand rough treatment. The

intended method of use is similar to the high-coal RHAM's discussed

above, except that disposable 9-V batteries power a red flashing lightemitting diode (LED).

Table 1 summarizes the two different types of RHAM units and the

three prototype units that were fabricated at PRC laboratories.

For More Information

For more information regarding this new technology, contact:

William D. Mayercheck or Albert L. Brautigam, National Institute for

Occupational Safety and Health (NIOSH), Pittsburgh Research Center,

Cochrans Mill Rd, P. O. Box 18070, Pittsburgh, PA 15236-0070,

Phone: (412) 892-6461, or (412) 892-6470, Fax: (412) 892-6567, email: wcm8@cdc.gov or aib4@cdc.gov

Mention of any company name or product does not constitute

endorsement by the National Institute for Occupational Safety and

Health.

To receive additional information about mining issues or other

occupational safety and health problems, call 1-800-35-

NIOSH (1-800-356-4674), or visit the NIOSH Home Page

on the World Wide Web at http://www.cdc.gov/niosh/

homepage.html 

As of October 1996, the safety and health research functions of

the former U.S. Bureau of Mines are located in the National

Institute for Occupational Safety and Health (NIOSH).

Table 1.—Roof hazard alert modules

Module Rechargeable Disposable No. 1 Disposable No. 2

Type ............................ Modified cap lamp Mechanical hook mount Magnetic-mount

Battery voltage ..................... One 4-V lead-acid Three 9-V dc alkaline Two 9-V dc alkaline

Battery life ........................ 1 shift+ 487 h 360 h

No. of shifts@4 h/shift ................ 3+ 121 90

Weeks@5 shifts/week ................ NAp 24 18

Operating life ....................... 5-6 years 5.6 months 4.1 months

Extension below roof bolt head .......... 11.5 in 4 in 2 in

Weight ........................... 5 1.2 6.2 lb 1.1 lb 1.5 lb

Overall dimensions .................. 12.5 in by 7.5 in by 6 in 5.25 in by 5.25 in by 1.25 in 5.25 in by 3.25 in by 1.25 in

NAp Not applicable.