Bump Test or Calibration Check?

Recently I was having a discussion with an end-user who was asking the question “should I be doing a bump test or a calibration check and what is the difference?”

Interesting question.  By most definitions, a bump test is a brief exposure of the monitor to gas in order to verify that the sensors respond and the instrument alarms function accordingly.  The bump test, by this definition, does not check the accuracy of the instrument.

This is where the calibration check comes in.   A calibration check is performed by exposing the monitor to a certified concentration of gas for a particular time to verify that it provides an accurate reading.

What was confusing to this customer was that the manufacturer of his monitor was telling him to bump test and verify the accuracy of the monitor before use but was not specifying how long the gas should be applied and what the reading tolerance should be.  Hmm….what should he do?

In most applications, knowing that the instrument will respond and produce an alarm that might save your life if a threatening gas hazard is encountered is all you need.   In other applications, the accuracy of the reading is more important.   With the instruments available today, if you are concerned about the accuracy of your readings before you use your instrument, you are better off to calibrate it rather than do a calibration check.  It will generally take the same amount of time, use the same amount of gas, and will guarantee the accuracy of the instrument readings when it is completed.  If you are doing a calibration check, and the readings fall outside of the desired or specified accuracy, you will have to do the calibration anyway, so you might as well do it the first time and get the guaranteed result.

In the end, it really doesn’t matter whether you choose to do the bump test, a calibration check or a full calibration.  Pick the one that is right for you.  The important thing is that before you take your gas monitor out and use it on a job where your life might be in danger, check it with gas in some manner.

Remember, the only way that you can be sure that your gas detector will respond to gas is to check it with gas.  Do it every time!



  1. Kevin York says:

    Dave- this has to be the most “time consuming” aspect of gas monitoring while dealling with end users today. The topic of bumping, calibration checks is the hottest topic and most widely misunderstood principle ( today),making manufacturers having to respond with complicated bump and docking stations; lengthy explanations on bump testing before or after eash test; to calibration not required but once every six months. Calibration frequency, by neccessity has always been application oriented.

    If end users, and the vendors that supplied them focused on the simple aspect- does the instrument work or not, perhaps you wouldn’t have to explain what they should already know. This does apply to what is mostly the 4 gas industrial safety instruments with OFCH cells, and pumps or no pumps. Use of pumps really does change “how” the calibration is done/ or bump test, or the length of tubing used to sample, so again, common sense really applies in even more depth and has to be included in their on site training by a qualified trained professional… like you.

    In the 80s, our instruments were accurate, reliable, and were $1500-$2500 for a 3 or 4 gas instrument, the sensors were “bigger”- perhaps less ergonomic or comfortable to wear, but they were TANKS!!!! We never had docking stations, bump checks other than to check for response to alarm ( the most important aspect in most cases right?), so I do have a question suitable for ask Dave. Are instruments today, personal 4 gas- that sell for $495 each- many with built in pumps, less accurate, less reliable than the older ones and SHOULD they require a docking station to document daily bumps or calibration set dates? Are these new “micro” sensors really capable of working accurately in rough industrial environments that are still the same as yesteryear? Exposure to gas on a daily, hourly or some fairly frequent basis certainly has to decrease the life of today’s sensors, or any electrochemical for that matter. So if they don’t really see gas in the field near the alarm points on regular basis, isn’t this bump testing, calibration tests- docking stations and data recording benefiting the manufactures more than the best interests of the end users?

    For vendors of instruments today, many of their products are now made in China, made in mass quantity, and all based on a market demand for the “cheapest” instrument out there. Surely the old addage- ” You get what you pay for” should apply?

    Any thoughts?

    Kevin D. York

  2. Dave Wagner says:

    Kevin – I do not subscribe to the theory that the smaller, lower-cost instruments available today are any less reliable than the “tanks” that you are referring to from the 80’s. Nor do I believe that the size or cost of the instrument has anything to do with how long it will last, how much gas exposure it will tolerate or how often it should be tested or calibrated.

    The use of portable gas monitoring instruments has proliferated since the 90’s and continues to grow into this decade. That extensive demand in the market has driven the size of the instruments down along with the price. That same demand has driven the manufacturers to produce the instruments along with systems and docking stations that make using them and maintaining them easier. I certainly don’t subscribe to the theory that only the manufacturers benefit from these systems.

    The fact of the matter is that gas monitoring instruments are secondary tools to the people that are carrying them. In most cases they do nothing to help the users get their primary job tasks accomplished. They are something that they would rather not have to carry or deal with at all. But they are required to have them by many laws and need to have them to save their lives at other times when the law doesn’t necessarily require them to be carried.

    As a manufacturer, gas monitoring instruments are our core business. It is our business to build them, maintain them, and train people how to use them. By providing docking stations that make the everyday test, calibration, documentation and other maintenance issues more simplistic for the instrument users, we are giving them more time to focus on their core business without having to worry about ours as well.

    The base sensing technologies of these instruments have not changed significantly over the years. There is no way to know that an electrochemical or catalytic gas sensor in a portable instrument will respond to gas without testing it with gas. There wasn’t in the 80’s and there isn’t today. As long as we continue to work toward our vision of ending death in the workplace, and gas sensing technology remains near its current state, we will continue to promote the best practices of bump testing and calibrating portable gas monitoring instruments routinely. This is clearly an area where we believe there is no room for compromise.

  3. Steve M says:

    Dave I sure hope you can help. I recently purchased a hydrogen “sniffer” leak detector. My principal use is to induce hydrogen in to lines, wait & let the hydrogen leave the leak & then use the “sniffer” to get “close” to the leak. The manufacturer has some very good technology re: a small hand-held unit but the support SUCKS. They tell me to “bump test” the unit every 90 days with a 2% hydrogen mixture. I cannot get them to tell me if that is 2% & air or if the hydrogen in the air makes up part of the 2%. The man I’ve dealt with is an “expert” in discussing the functioning of his instrument, but when it comes to questions like I just stated he can only repeat, 2% hydrogen mixture……am I making this to hard. The manual is made for “technicians” & not people that work everyday in the “field”. My livelihood & income is dictated by my/our resourcefulness in a specialized market. He’s tired of me calling to ask particulars & I even “snuck in” an email to the technical staff & still no response. I did a lot of research, but my simple questions are apperently not suited for a “technical person”, am I making any sense.
    I have another question this guy won’t answer; but I’ll ask latter & then wait for the first one to be answered….is a 2% mix disregard the H in the air.
    The second question I think is chemically simple, but this guy says thai’s not “in his field”.
    Hope I’ve not been a pain, but I need some help.

    Steve M

  4. Dave Wagner says:


    I am fairly certain that the manufacturer is talking about a mixture of 2% hydrogen in air. That should be available from most of the gas manufacturers.

    I will be happy to provide you support where I can, but it is always difficult to provide answers on someone else’s products.

  5. Steve says:

    Dave, i want to thank you for your input re: “Bump Test”. the gentleman’s reply is a tad bit more complex but i understand his point. i’d like to tell you the manufacturer is but i have to give them another opportunity to ask my questions. i know i probably made them tired of answering questions, but i bought their unit after researching using helium as the medium for leak detection. knowing that hydrogen is the lightest element this combo of 95% nitrogen & 5% hydrogen is supposed to offer a much more advantageous method of leak detection. see, all we really do is pool, water lines & such on a mom & pop level. so using this new technology in the midwest is suppose to give us the best system to do so. this is more of a comment than a question, but i’m searching for a place to go for my technical questions i just haven’t found a place yet; however i do have a question re: using this combo of gases. Can one use this combo to place in a pipe that already has water in the pipe? doesn’t make since that you can because of the H2O having 2 molecules of hydrogen. i’m just wondering if the combo can pass through the water because of their structure. some say helium will because it is the lightest inert gas others say it won’t. i appreciate your efforts Steve

  6. Dave Wagner says:


    As I said, I will help you as much as possible. I don’t see any problems in terms of being able to pass the hydrogen gas through the water. There should not be any reaction there that I am aware of.

  7. Amarachi Iroapali. says:

    Good evening sir, am a young Nigerian Engineer and i have been given the task of conducting gas test at one of my employers’ site. my problem is when ever i run a bump test, only the oxygen alarm responds. The hydrogen sulphide, combustible gas and carbon monoxide does not respond to my bump test. What can i do?

    thanks in anticipation

  8. Dave Wagner says:

    What type of gas are you using to perform the bump test? It does not appear that you have the gases necessary to make the other sensors respond.

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  19. Carol says:

    I worked with a docking station for 6 H2S monitors and have many questions. Firstly, I wanted to find out if Dave is still answering questions here.

  20. Dave Wagner says:

    Hi Carol – yes I am still answering questions here. Rather than comment on a post, you may be better off to use the “Ask it Here” button or just send your question to me directly to dwagner@indsci.com. Look forward to hearing from you.


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