Bump testing versus calibration: What you need to know

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You have likely heard people using the terms “bump testing” and “calibration” interchangeably. However, learning to distinguish between a bump test and full calibration is aids in safe use of direct-reading portable gas monitors (DRPGMs) to check oxygen levels and detect gases that could be toxic or combustible in a work environment. Devices must be properly maintained and calibrated to help prevent injury, death, and property damage from explosions resulting from flammable gas and exposure to other gas and oxygen-level hazards. Ideally, a user will test a DRPGM before each use with a known concentration of gas to assess the accuracy and reliability of the alarm.1

Regulation

The International Safety Equipment Association (ISEA) is a leading trade association for safety equipment manufacturers and testers whose goal is to protect workers by developing relevant standards and providing education pertaining to maintaining safe workplaces and avoiding exposure to hazards.1,2 This includes DRPGMs. Specifically, for these devices, ISEA recommends daily bump tests or calibration checks based on manufacturer guidelines to ensure proper function in addition to more extensive full calibration when needed, or in the case of failed bump tests or calibration checks. In addition, following a failed full calibration, the device must be pulled from use.1 As such, the organization released a statement in 2010 “to ensure definition consistency in all documentation, and to emphasize the need to validate the operational capability of portable gas monitors.”2 The statement distinguishes between a bump test or “function check,” calibration check, and full calibration; specifies conditions under which each method is appropriate; and stresses the need for testing protective equipment.

Bump Test

According to the ISEA, a bump test is a “qualitative function check where a challenge gas is passed over the sensor(s) at a concentration and exposure time sufficient to activate all alarm indicators to present at least their lower alarm setting. […] This is typically dependent on the response time of the sensor(s) or a minimum level of response achieved, such as 80% of gas concentration applied.”2 The test verifies that the sensor and accompanying alarms function appropriately and also can inform users when a blockage prevents gas from reaching the sensor. A bump test checks for function rather than assesses accuracy of calibration.

Perform a bump test daily before using your DRPGM, and follow the device manufacturer’s instructions. If your DRPGM fails the bump test, conduct a full calibration, which the instrument must pass within two attempts before you can use it.2

Calibration

To determine the accuracy of a DRPGM, you can perform either a calibration check or full calibration depending on various conditions.1

Calibration Check

Per ISEA’s statement, a calibration check is a “quantitative test utilizing a known traceable concentration of test gas to demonstrate that the sensor(s) and alarms respond to the gas within manufacturer’s acceptable limits.”2 You will start by resetting your instrument to the manufacturer’s recommended reference point, or “zero” it, then apply test gas in a high enough concentration to set off any alarms. Following application of test gas, the user will compare the sensor reading to the concentration marked on the container of test gas. The acceptable range1 indicating verification of the device’s accuracy is “typically ±10-20% of the test gas concentration applied unless otherwise specified by the manufacturer, internal company policy, or a regulatory agency.”2 Always confirm your DRPGM’s acceptable range with its manufacturer.

Perform a calibration check each day prior to use and according to instructions from the device’s manufacturer.2 As with a bump test, should results of a calibration check fall outside of the acceptable range, you will need to follow up with a full calibration.1

Full Calibration

The ISEA defines full calibration as “[t]he adjustment of the sensor(s) response to match the desired value compared to a known traceable concentration of test gas” based on drifting that naturally occurs because of time or environmental conditions. Only qualified, trained personnel can perform this testing, following their manufacturer’s instructions along with internal policy or recommendations from a regulatory agency for how to perform full calibration and to identify the intervals at which you should fully calibrate your DRPGM.2

Although full calibration often does not occur as often as a bump test or calibration check, the ISEA says that you should fully calibrate your instrument in circumstances including exposure to the following2:

  • High concentrations of target gases and vapors
  • Chronic extreme environmental conditions
  • Poisons and inhibitors
  • Solvent vapors and highly corrosive gases
  • Harsh storage or operating environments
  • Change in operator or working conditions

Daily calibration is desirable in case any of these incidents occurred.

Although operators always need to refer to the product manual, they should, in general:

  • Calibrate in fresh air
  • Use a recommended gas mixture
  • Choose calibration gas that meets the National Institute of Standards and Technology (NIST)
  • Test in an environment mirroring the conditions of the workplace
  • Ensure the gas’s expiration date has not passed

Keeping records is also a must.. The Occupational Safety and Health Administration (OSHA) will want to see one year of testing data (bumps and calibrations) in the event that an incident occurs in which the user is injured or exposed in a reportable event.

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A bump test or calibration check tests for the presence of potentially hazardous gas; full calibration verifies equipment accuracy. Knowing when to perform each to keep your DRPGMs functioning as intended can help keep you or your workers safe from exposure to toxic gases or combustion.1

MSA, The Safety Company, offers a range of calibration gas, kits, and accessories with instructions that reflect best practices. For example, while some other manufacturers tout a less frequent need for bump testing and calibration as a benefit, MSA product instructions follow ISEA recommendations to help prevent personal injury and property damage. Included in these offerings is a complete line of calibration gas cylinders to calibrate all instruments. MSA calibration gas is the only gas with auto-setup, and it meets the NIST standard. MSA applies an RFID tag to each bottle, which fully automates the calibration gas setup process, minimizing potential errors. A true partner in comprehensive safety training, MSA also offers courses for workers to learn to maintain and repair instruments.

References

  1. http://safetyequipmentfaq.com/wp-content/uploads/2014/01/OSHA-calibration-information-bulletin.pdf
  2. https://safetyequipment.org/wp-content/uploads/2015/09/calibration_statement-2010-Mar4.pdf

AUTHOR BIO

Jason Fox has been with MSA Safety for over a decade and is currently the Customer Marketing Manager for Portable Gas Detection with a focus on the utilities market.

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