O H & S suggests that a bump test “should be conducted before each day’s use in accordance with the manufacturer’s instructions.” Based on O H & S suggestion, the matter of bump test frequency is to be decided by the manufacturer’s instructions. Oxygen deficiency, exposure to toxic gases and explosive atmospheres are all too often responsible for workplace incidents, injuries and fatalities.
A gas detector is an important piece of safety equipment. Workplace environments can be harsh and gas detectors are subjected to rigorous environmental conditions in a variety of applications that can affect operation. Instruments can become physically damaged. Catalytic bead combustible gas sensors are particularly prone to airborne poisons or substances that can inhibit their ability to respond to combustible gas. Sensors can be damaged by gas concentrations that exceed their detectable limit. Sensor ports on the instrument can become obstructed by liquid and particulate materials that can prevent the movement of the target gas.
Bump testing of any gas monitor will move up the filters faster than on a unit that is not being bump tested. All 4 gas monitors have a charcoal filter on the CO sensor, and daily exposure to the H2S in a bump test cylinder will shorten the life of the charcoal filter, thus requiring more frequent maintenance of the filter. No matter what is used for the bump or calibration frequency, it is recommended that a bump or calibration be performed immediately if there is ever an incident, if the unit gets exposed to a high gas concentration, if the unit receives a large physical shock or is exposed to silicone poisons.
O H & S defines a bump test as “a qualitative function check in which a challenge gas is passed over the sensor(s) at a concentration and exposure time sufficient to activate all alarm settings.”
In English, the bump test is the process that verifies “the performance of the gas detector and ensures that sensors are responding to their target gas.” For example, an H2S sensor is exposed to H2S gas to verify it can respond. As you might imagine, the sensor is the most important component inside a gas monitor. When facing an unknown gas hazard, you need a sensor that provides dependable detection of combustible atmospheres. It quickly should respond to explosive gases and have a high level of sensitivity to combustible organic vapors in a confined space. The monitor you choose should include sensors for:
➤ O2 – To check the oxygen level for deficiency or enrichment.
➤ Combustible gas – To test for levels of flammable or explosive gases.
➤ Toxic gas levels – Typical confined space monitors have hydrogen sulfide (HS) and carbon monoxide (CO) sensors; additional toxic sensors may be used based on the application.
A bump test does not calibrate the sensors. What we generally recommend is that users develop a frequency of calibration that is tailored to their application and usage. Initially, the user may begin by calibrating once per week, and note any changes or adjustments needed to the calibration. If, week after week, there is very little or no adjustment needed, then the calibration frequency can decrease to the point that there will be only a small adjustment needed when calibrating. The problems is manufactures doesn’t spell out how often “periodically” is. The manufacturer seems to equivocate on their claim the monitors are “zero maintenance” and “operate for the full two years without calibration” with this call for periodic bump testing. We understand calibration is not bump testing. But either one is certainly maintenance.
A precaution to note.
It is generally recommended that a bump test or calibration be performed if it is suspected that the instrument has been subjected to any condition that could have an adverse effect on the unit (sensor poisons, high gas concentrations, extreme temperature, mechanical shock or stress, etc).
Use of Current Monitoring Technology
Although H2S detection and monitoring practices vary by industry and the location of company operations (state, province, country, etc.), the prevailing methods in the workplace are detector tubes and instrumentation that uses electrochemical sensors. While some detectors can continuously collect gas concentration data from a fixed location in a monitored area, historically, few companies have actually built an archive of such data. If they did, this would allow them to establish ceiling limits in a quantitative manner, similar to the way ACGIH did in establishing its current H2S TWA and STEL values. The 2010 ACGIH guidelines provide an impetus for companies to collect HS monitor data, which would allow them to evaluate and refine their safety and hygiene programs.
Important Features in Portable/Personal Monitoring Equipment
- Look for the ability for several sensors to be installed in the unit that can be selected from a list that includes CH, H2S, SO, CO, O, H2, NH, HCN, NO, NO, and others.
- Simple bump test station and a traceable bump test mode; bump testing every day is recommended to check sensor accuracy, stability, and response time and verify proper operation of the display and alarm functions.
- A variety of power supply options: Lithium alkaline or rechargeable NiMH battery supplies with charging module and charger are popular ones.