Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, TN 418, 1993 Apr; :1-2
Objective: Determine the appropriate spacing and alarm levels for carbon monoxide and smoke sensors used for fire detection in underground coal mine conveyor belt entries. Background: Fire represents one of the most severe hazards in underground coal mines. Early-warning fire detection in underground coal mines is essential to successfully implement and execute evacuation and control measures. Both carbon monoxide (CO) and smoke sensors have the ability to provide reliable early-warning capability, provided that they are spaced properly and set at the appropriate alarm levels. The U.S. Bureau of Mines conducted a series of large-scale experiments where a small coal fire was used to ignite a conveyor belt at air velocities of 0.76 to 6.1 m/s. The test configuration was purposely designed to model a worst-case fire scenario for fires that develop within conveyor belt entries in underground coal mines. During the tests, CO and smoke levels were continuously measured to determine alarm times and alarm levels as the fire intensity progressed. The data from these tests indicated that for a given sensor spacing, the time to reach a preset alarm threshold depends upon the belt entry air velocity and cross-sectional area. Analysis of this data resulted in the equations and nomographs for CO and smoke sensor spacing and alarm levels contained in Bureau of Mines RI 9380, "Fire Detection for Conveyor Belt Entries." Approach: The sensor nomographs are simple to use if the belt entry is simple and fairly well defined with an average air velocity and an average cross-sectional area. However, typical underground conveyor belt entries may be complex. Many may contain crosscuts that should be considered for fire detection plans. Parallel entries, which are not separated from the conveyor belt entry by permanent stoppings, may exist along the length or along some section of the conveyor belt entry. Air splits, where ventilation air is diverted into or out of the entry, may occur at various locations along the belt entry. To readily account for these complexities, a flexible, user-friendly, personal computer (PC)-based program called "CASSAL" was developed. It takes information entered by the user and constructs air velocity and cross-sectional area profiles of the conveyor belt entry. The profiles are then used to determine the appropriate CO alarm thresholds and smoke sensor class (see RI 9380) for sensors installed in the belt entry. Within the framework of this program, it is possible to handle extremely complex ventilation airflows and entry configurations. How It Works: The program prompts the user to input information describing the mine entry. This information includes the length and cross-sectional area of the entry; location of belt drives, and air splits; the cross-sectional area, location, and number of parallel entries; the depth and spacing of cross-cuts; and the air velocity in regions along the entry. The sensor positions are calculated using 1,000 or 2,000 ft maximum spacing. To separately protect each belt drive, a sensor is installed 100 ft downstream of each belt drive. Subsequent sensor positions are based on the maximum spacing. Sensor locations are the same for both CO and smoke sensors and are independent of ventilation airflow, but depend upon the location and number of belt drives. Based upon the user input information, complete cross-sectional area and velocity profiles of the entry are constructed. Using these "maps" of the mine entry, the program calculates the individual sensor alarm levels. Along the length of a belt entry, the conditions of air velocity and entry cross-section can change, often dramatically. For these situations, sensor alarm thresholds may also change from one sensor to the next. When different sensor alarm levels result from the "maps," the program averages the alarm levels and arrives at a final, single alarm level for all sensors. The end product of this program is a listing of the number of sensors required in the belt entry, the locations of the sensors (using 1,000 or 2,000 ft maximum spacing), the alarm levels for CO and smoke sensors, and the average alarm time for all sensors within the belt entry.
Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, TN 418