Question: I am a Canadian instrument user with a GfG G460 multi-sensor instrument. The instrument is equipped with sensors for the measurement of LEL combustible gas, O2, CO, H2S and hydrogen cyanide (HCN). I am currently performing a bump test on all of the sensors every single day. The biggest issue is the cyanide sensor. It takes longer to complete the bump test for the cyanide sensor than the other sensors, and the cyanide calibration gas is very expensive. What are the manufacturer requirements in regard to performing a daily bump test?
Answer: Thank you for your request for clarification regarding GfG’s requirements for performing a bump test before each day’s use. As a manufacturer, to a certain extent our hands are tied by the standards to which our instruments are certified. However, the requirements may not be as onerous as they appear at first glance.
GfG does not explicitly require that a bump test (function test) be performed on all sensors before each day’s use. The exact wording we use in the G460 manual is:
GfG recommends that you “bump test” the sensors before each use to confirm their ability to respond to gas. To do this, expose the detector to a gas concentration that exceeds the alarm set points. Manually verify that the audible and visual alarms are activated. Calibrate if the readings are not within the specified limits.
From the GfG manufacturer standpoint, use of the term “recommends” indicates the decision is up to the customer. In the United States, instructional guidance letters published by OSHA suggest performing a bump test before each day’s use. However, the OSHA guidance letters are non-mandatory, and in most jurisdictions in the USA, it is still up to the customer. Provincial authorities in Canada generally view the issue differently.
To be legal for sale in Canada, all instruments that include a sensor for the measurement of LEL combustible gas must be certified as Intrinsically Safe according to Canadian requirements. Canadian Standards Association C22.2 NO. 152-M1984 (R2001), “Combustible Gas Detection” is the CSA standard that covers the details of construction, performance, and test procedures for portable instruments used to detect or measure combustible gases in hazardous locations characterized by the known or potential presence of combustible gas. Section 5.3, “Instruction Manual” lists the minimum information and warnings that must be included in the owner’s manual of gas detectors that are compliant with this standard. Paragraph (k) includes the following statement:
CAUTION: BEFORE EACH DAY’S USAGE SENSITIVITY MUST BE TESTED ON A KNOWN CONCENTRATION OF _____ (SPECIFY GAS) EQUIVALENT TO 25-50% OF FULL SCALE CONCENTRATION. ACCURACY MUST BE WITHIN -0-+20% OF ACTUAL.
In other words, to comply with Canadian requirements, the performance of the combustible sensor must be verified by exposure to known concentration combustible gas before each day’s use. This does not come from the manufacturer, it comes from CSA. It is this statement from CSA 22.2 that makes testing the LEL sensor before each day’s use mandatory for many Canadian customers.
You will notice that the standard only refers to testing the performance of the combustible LEL sensor. It does not include a requirement to test other sensors installed in the same instrument. However, some provinces locally require users to perform a bump check on all sensors, (especially the basic sensors in a typical four gas LEL / O2 / CO / H2S instrument), before each day’s use. It may be a good idea to contact the local provincial Ministry of Labour office to confirm the requirements in your area.
While CSA 22.2 defines the pass fail criteria to use when testing the LEL sensor, the standard does not provide guidance on the pass fail criteria to use when testing other types of sensors. GfG uses the definition of “bump test (function check)” developed by the International Safety Equipment Association, (ISEA) and referenced by USA OSHA in instructional letters to USA instrument users. Per the ISEA / OSHA definition, during a bump test (or function check), the accuracy of the sensor readings is not verified or adjusted. The bump test simply verifies that the sensors respond and the alarms are properly triggered when the instrument is exposed to a concentration of gas high enough to cause the activation of the alarms. For the LEL sensor you should stick with CSA pass / fail criteria. For the other sensors, from the GfG standpoint, all you need to do is verify that the alarms are properly activated when the sensors are exposed to gas. Any sensor which fails a bump test must be calibrated, and be found to perform properly before further use.
From the GfG standpoint, as long as the local Canadian authorities agree, based on user experience with the instrument, it may be possible to lengthen the interval between performing a bump test on sensors not used to measure LEL explosive gas. When we are asked for guidance, GfG suggests using the following criteria to help decide whether or not it is prudent to lengthen the interval between bump tests:
- During a period of initial use of at least 10 days in the intended atmosphere, calibration should be verified daily to be sure there is nothing in the atmosphere which is poisoning the sensor(s). The period of initial use should be of sufficient duration to ensure that the sensors are exposed to all conditions that might have an adverse effect on the sensors.
- If the tests demonstrate that it is not necessary to make adjustments, then the time interval between checks may be lengthened but should not exceed 30 days.
- The history of the instrument since last verification can be determined by assigning one instrument to one worker, or by establishing a user tracking system such as an equipment use log.
- Any conditions, incidents, experiences, or exposure to contaminants that might adversely affect the calibration should trigger immediate verification of calibration before further use. Most importantly, if there is any doubt about the calibration of the sensors, expose them to known concentration test gas before further use.
GfG DS-404 automatic test and calibration docking stations significantly simplify calibration and testing procedures, and can greatly reduce the cost by reducing the amount of gas and time required. For instance, GfG docking stations can be set up to test the LEL sensor on a daily basis using inexpensive single-component LEL test gas. The docking station can be set up to test the other sensors using gas from different cylinders on a less frequent basis. There is no need to include all of the sensors every time the docking station performs a bump test on the instrument. Which sensors are tested is up to our customers.
Thanks again for your inquiry.