Miners
have been known to unknowingly venture beyond the last row of roof bolts in underground coal mines. To help discourage miners from going under unsupported mine roof, NIOSH
researchers have developed two flashing light roof hazard alert devices that direct a miners attention to a written message, warning the miner to avoid
the hazard beyond the device.
Learn more in the Technology News Article Roof Hazard Alert Modules (PDF, 98 KB)
How It Works
Two different types of battery-powered roof hazard alert devices have been designed, fabricated, and evaluated at the Pittsburgh Research Laboratory. One type features a rechargeable cap lamp battery for its energy source; the other, smaller unit uses disposable 9-V alkaline batteries and it was certified by MSHA as being intrinsically-safe. Both devices mark the end of roof support with a flashing red light and a written message warning miners to avoid the unsupported area ahead.
The rechargeable unit (photo on the left) was fabricated from a conventional 4-V cap lamp battery unit. A special circuit interrupts the conventional incandescent bulb to flash through a red lens at about 3 Hz. The added electrical circuit is a low power, energy storage design and is expected to be amenable to an MSHA-certified, intrinsically safe permit for operation beyond the last open crosscut in a gassy mine.
At those places underground where mining has progressed 4 ft beyond the last row of roof bolts, a roof hazard alert unit is suspended from a roof plate eyelet within the last row of roof bolts and rotated so that the lamp is facing out. The unit hangs about 1 ft below the roof, which allows for most personnel and equipment movements underneath in higher coal seams. In lower seams, the compact roof hazard alert is recommended. Two different versions of this design were tested; one uses a hook mount similar to the high-coal version, the other (photo on the right) features an internal magnetic mount that minimizes the projection below the mine roof
The table below summarizes the three different types of roof hazard alert units that were built and tested.
| 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 | Not applicable | 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 | 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 |