Environmental and Occupational Health

The daily "bump test": Best practices for assessing portable gas meters

Workers cannot rely on their senses to alert them to hazards in the workplace. Exposure to excessive levels of toxic gas or an oxygen-deficient environment can cause workers serious illness and even death. Combustible gas explosions are often catastrophic, injuring or killing personnel and destroying property.1 Designed to protect workers from such unforeseen dangers, gas monitoring instruments are often utilized to measure, monitor and indicate the concentration of certain gases in the atmosphere.

It is vital to worker safety that these instruments are maintained and calibrated properly. In addition, performance of a daily bump test prior to use of gas detectors is a best practice because it is the only method by which the entire system — instrument, sensors, flow path, power source, alarms and all electronics — can be checked to ensure it is functioning properly and that gas can reach the sensor. Additionally, bump testing and calibration records can be recorded on most detectors to help to ensure compliance, traceability and proper record-keeping.

" It is recommended that a thorough evaluation of the detectors,specifications, sensors and warranty information be conducted prior to any purchase. " 

Best practice

The best practice of conducting a daily bump test on portable gas detectors is acknowledged amongst nearly all safety professionals, manufacturers and users of gas detectors. Implementation and adherence to this practice, however, is not always a priority, with time, expense and logistical concerns frequently cited as reasons for noncompliance. Further, as product durability and advancements in sensor technology continue to improve detector performance and reliability, some are using these improvements as a basis for abandoning the practice of daily bump tests that has resulted in some deviation from the best practices and could prove detrimental from both a compliance and safety perspective.

 In general, most manufacturers have historically recommended a daily bump test prior to the operation of gas detectors. Not to mention, several organizations such as the European Committee for Electrotechnical Standardization (CENELEC), International Electrotechnical Commission (IEC), International Safety Equipment Association (ISEA) and OSHA continue to advocate a best practice of a daily bump check for portable gas meters.

Most manufacturers have also developed sophisticated automated testing systems which have helped to simplify testing and eliminate some of the logistical barriers to compliance. In addition, improved sensor technologies that require relatively little or no bottled gas to achieve a successful bump test have emerged and help to reduce expenses associated with bump testing.

Reasons for bump testing

There is no disputing the fact that there have been tremendous advances in detector technology and durability. For that reason, it is more important than ever before to maintain a good understanding of the instruments that will be put into use. It is recommended that a thorough evaluation of the detectors, specifications, sensors and warranty information be conducted prior to any purchase.

It is important to note that all detectors may be susceptible to the failure modes identified by OSHA (below) and others. Although most detectors have been designed for durability, bump testing still needs to be conducted daily as a best safety practice.

The “ISEA Statement on Validation of Operation for Direct Reading Portable Gas Monitors,” March 5, 2010, clearly states, “A bump test (function check) or calibration check of portable gas monitors should be conducted before each day’s use in accordance with the manufacturer’s instructions.” What has happened is that many users, and some manufacturers, have interpreted this to mean bump testing less frequently is now an acceptable practice. However, performance of a daily bump test is the only method by which the entire system: instrument, sensors, flow path, power source, alarms, and all electronics can be checked to ensure that the instrument is functioning properly.

Instrument inaccuracy due to improper or irregular calibration can lead to serious accidents. Over time, the accuracy of gas detection instruments can diverge from their calibration settings in several ways. According to OSHA Safety and Health Information Bulletin 05-04-2004, the following are the potential failure modes that can be identified during a bump test:

1) Gradual chemical degradation of sensors and drift in electronic components that occur naturally, over time;

2) Chronic exposures to, and use in, extreme environmental conditions, such as high/low temperature and humidity, and high levels of airborne particulates;

3) Exposure to high (over-range) concentrations of the target gases and vapors;

4) Chronic or acute exposure of catalytic hot-bead LEL sensors to poisons and inhibitors. These include: volatile silicones, hydride gases, halogenated hydrocarbons, and sulfide gases;

5) Chronic or acute exposure of electrochemical toxic gas sensors to solvent vapors and highly corrosive gases;

6) Harsh storage and operating conditions, such as when an instrument is dropped onto a hard surface or submerged in liquid. Normal handling/jostling of the equipment can create enough vibration or shock over time to affect electronic components and circuitry; and

7) In addition to aforementioned, any general component failure.

It should also be noted that paint, aerosols, mud and other debris will frequently block sensor inlets.

Reinforce safety practices

In addition to good maintenance practices, safety practices also need to be reinforced regularly. Far too often, gas alarms are viewed as a nuisance or an error and are ignored by workers. It is critical workers comprehend the fact that the detector is utilized for their safety. Following safety protocol when alarms are triggered is a critical safety practice and could prove to be lifesaving.

Too many variables

Although some will continue to debate the need and frequency of bump testing, CENELEC, IEC, ISEA and OSHA continue to recommend a daily bump check for portable gas meters. It is important to understand that there are multiple reasons for that. Too many variables remain that can negatively impact instrument performance. So, until these variables can be eliminated, it is clear that the current bump test recommendations should remain the industry standard to ensure daily readiness of detectors. Simply put, a bump test prior to each day’s use helps to maintain worker safety.


1 U.S. Department of Labor, Occupational Safety and Health Administration, Verification Of Calibration for Direct-Reading Portable Gas Monitors, (05-04-2004), www.osha.gov/dts/shib/shib050404.html.

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