How to ensure Safety?

Calibration vs Functional (Bump)Test Differentiate between calibration and functional (bump) test functional test –the sensors are simply exposed to known concentration test gas. –The readings and performance of the alarms are verified, but not adjusted. –As long as the functional test indicates readings are accurate, there is no obligation to adjust the sensitivity of the sensors. Calibration –the readings of the sensors are actually adjusted (if necessary) to match the concentrations in the calibration gas.

FUNCTIONAL (BUMP) TEST Many companies take the approach of doing a daily functional test. –This is a great approach IF it is logistically feasible. Other companies with a long experience of using confined space gas detectors (like New England Grid) find that they are safely able to extend the period between calibration checks. Some perform functional (bump) tests on a monthly basis. Other companies do a full calibration on instruments only once every 180 days. BW personnel are not the ones using the instruments in the field –not in a position to dictate the frequency of testing.

CALIBRATION We base our recommendations on the very conservative International Safety Equipment Association (ISEA) protocol for lengthening the time between testing the calibration of sensors in instruments used to monitor confined space atmosphere. –The ISEA protocol suggests performing a functional test at least once every 30 days. –There is no set interval for performing a calibration –Customers are free to calibrate their instruments once every 180 days, or choose an even longer period between scheduled calibrations IF they are able to verify through experience that this is a safe and prudent interval. It's up to the instrument user to verify that the interval specified is safe and prudent. If there is any doubt, a shorter interval between calibration checks should be specified.

RE-VERIFICATION Any conditions, incidents, experiences, or exposure to contaminants that might adversely affect the calibration –should trigger re-verification of calibration by performing a functional (bump) test before further use. –If there is any doubt about the calibration of the sensors, they should be exposed to known concentration test gas before further use.

BUMP TEST FOR CL2 AND HCL Sensor Typical Response Time –Catalytic sensor T90 <= 30 seconds (methane) T90 <= 10 seconds (hydrogen) –Infra-red sensor T90 <= 10 seconds –Electrochemical sensors CO/ H2S –T90 <= 30 seconds Cl2/ HCl –T50 <= 30 seconds –T90 <= 70 seconds –CL2/ HCL sensor Bump gas and wait for 4 minutes for sensor to stabilise Bump gas and check for sensor response at 50% response after 30 seconds

OXYGEN SENSOR Oxygen Sensor has a finite life the length of their operating life will be determined by the total exposure to Oxygen. This is because the sensor has a metal anode which is consumed by the reaction mechanism. The characteristic of Oxygen Sensor is that they have a stable signal output, which experiences minimal decline, right up until the end of the sensors life. At the end of the sensor's operating life there is a sudden and rapid drop-off in output as the sensor's anode is finally consumed.

BUMP TEST FOR O2 SENSOR A ’bump’ test is a means of verifying that an instrument is working within acceptable limits by briefly exposing to a known gas mixture formulated to change the output of all the sensors present. This is different from a calibration where the instrument is also exposed to a known gas mixture but is allowed to settle to a steady figure and the reading adjusted to the stated gas concentration of the test mixture. For oxygen monitors a level of confidence that the unit is working adequately may be gained by exhaling over the sensor inlet and viewing the reduction in reading obtained. In many cases the reduction in Oxygen concentration obtained is sufficient to trigger the low oxygen alarm.

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