When using hand held gas detection instruments in underground in coal mines, a crucial step is the testing of each gas detection instruments prior to use.
Span test/span check or function test in coal mines is the process of testing a gas detection instruments with a known quantity of calibration gas for a specific length of time and determining whether the response(reading) is accurate in relation to the known concentration.
Typically for methane the concentration would be 2.5% volume methane and the response test reading must be between 2.3% to 2.7% for the instrument to be used.
If the reading does not come within the range then the instrument cannot be used and would be taken back for calibration.
Similar response testing would be conducted for the other sensors in each instrument such as carbon monoxide, carbon dioxide, nitrogen dioxide or oxygen.
To test all instruments being used underground, methods or systems to reduce the time taken for testing need to be considered.
When you have instruments being response/function tested regularly, it is useful to evaluate the use of larger volume gas cylinders. These larger cylinders of gas mixtures can improve the efficiency of your bump testing program, while decreasing costs (read blog on 10 key factors for efficient gas detection docking station systems).
The larger the gas cylinder the lower the cost per litre. Using our gas calculator, you can determine your annual gas volumes and then determine the size of cylinder which best meets your needs in cylinder sizes ranging from 34 to 7500 litres. By connecting either a fixed flow and an on-demand flow regulator directly to a high pressure/large volume cylinder, it’s the same as using small disposable cylinders but with increased efficiency.
To increase the number of instruments you can test at the same time, a gas panel can be added which can have two, three or more outlets to allow you to test multiple instruments simultaneously.
Response/Function Test Stations:
Today there are several types of test stations which can be installed above ground or underground for quick and easy testing of gas detection instruments. Some test stations are mains powered which provide you the ability to set the flow rate and the length of time the gas flows. This style of testing station can only be used above ground, reducing the efficiency for workers underground.
The latest innovation is the pneumatic bump test station, developed by CAC Gas & Instrumentation, which runs off the calibration gas used. Simply bolt on the wall and connect your calibration cup and, with a press of a button, you can test two instruments at the same time. With no power or batteries, this system can be located anywhere, including underground, and you don’t have to worry about gas loss as the system turns off by itself. Capable of being used with either disposable or large volume cylinders, these response test stations take the “manual” out of manual testing.
Pneumatic response test stations are extremely useful when there are numerous gas detection instruments being used. Having the response testing station right in the work area saves time and money. Miners can use the system underground to response test instruments or zero instruments using zero air without the need to come to the surface.
A key element of most bump test stations is they are generic and can be used with any gas detection instrument. This provides real benefits for customers who have multiple types or brands of gas detectors.