The Dos and Don'ts of Atmospheric Testing

Common pitfalls to avoid with atmospheric testing in confined spaces.

• By Dave D. Wagner
• Sep 18, 2019

Atmospheric testing plays an important role in keeping workers safe in the construction industry. Like the OSHA general industry standard, the construction safety standard requires testing the atmosphere to verify that it is safe before anyone enters the confined space. 

Every atmospheric testing program associated with confined space entry is filled with choices that ultimately affect the safety of workers as they perform their daily duties. Typically, the program is far from the core competency and productive focus of the company. Too often, this causes the program to concentrate on doing only what is necessary to comply with the rules.

While you should regularly review your own gas detection program to ensure compliance with standards and best practices, below are some of the com - mon pitfalls to avoid with atmospheric testing in confined spaces.

Wrong sensors for the job. The most fundamental mistake in an air monitoring program is using the wrong detection equipment. Somewhere along the way, a portable confined space gas monitor be - came defined as a four-gas instrument which detects oxygen, combustible gas, carbon monoxide, and hydrogen sulfide. While sensors for two of those components, oxygen and combustible gas, are a must in almost every confined space application, the other two are not. Confined spaces are all different, and the hazards found in them will vary. Properly assessing the potential hazards and ensuring that the detection equipment is capable of effectively monitoring the hazards in your space is critical.

No remote sampling equipment. Confined space entry regulations require that the atmosphere is tested and cleared of hazards prior to a worker entering the space. Workers will often lower gas monitors into a hole using rope, which can damage equipment and lead to expensive repairs.

Bad zero references. It’s natural to get to the job, turn your monitor on, look at the readings, and initiate a zeroing function. However, this is often done without knowing whether the atmosphere you are standing in at the time is suitable for establishing a zero reference on the instrument. Before zeroing, you must be certain that your environment is free of gas contaminants. If you zero an instrument in the presence of gas contaminants, the instrument will likely display negative gas concentrations in a clean atmosphere. If your instrument is not capable of displaying negative readings or automatically zeros during start-up, you likely will never know if this mistake has been made.

Improper calibration. An instrument is only as accurate and reliable as its calibration. The key to a good calibration is verifying that the gas concentration listed on the cylinder label matches the concentration setting for calibration in the instrument. It sounds easy, but the instances of instrument users picking up a cylinder of gas at one concentration and using it to calibrate an instrument requiring a different calibration gas reference are too numerous to overlook.

Failure to test the equipment before use. The only way to be certain that your instrument detects gas is to bump test before you use it. Performing a bump test or functional test on a gas monitor is simple and takes only a few seconds. Would you trust your life with a piece of equipment without knowing if it works? Would you be comfortable stepping onboard an airplane if you knew that the pilot did not perform the required pre-flight inspection? Don’t skip the pre-flight check on your gas monitor.

No correlation between oxygen and combustible gas readings. Many people overlook the fact that sensors for detecting combustible gases need oxygen to provide an accurate reading. If the oxygen concentration in an environment is below 10 percent, the sensor will not function properly, and a dangerous condition may go undetected. The best practice is to always ensure a valid correlation between the oxygen and combustible gas readings on your instrument before assuming a safe atmosphere.

Test it and forget it. Regulations require testing the atmosphere prior to entering a confined space. When the testing is complete, the instrument often goes back in the truck. Atmospheric conditions can change quickly and dramatically. Because all is clear and safe now is does not mean that it will be safe 15, 30, or 60 minutes from now. Regulations require continuously monitoring the atmosphere to be sure it stays safe. Keep the instrument out and continue monitoring the atmosphere as long as the work continues.

Lack of training. Workers are often handed an instrument, assigned to perform the atmospheric test, and sent on the job without any understanding of how to operate the instrument or interpret its readings. Training tools are plentiful. Videos, computer-based training modules, online tutorials, and personalized seminars are all readily available to help convey the knowledge and competency necessary for using gas monitors. Don’t go to work without understanding the equipment and how to use it properly.

Misinterpretation of readings and data. Many people falsely believe that when they know a hazard exists that they cannot identify, they can take their portable gas monitor into the area and it will tell them what the problem is. Nothing could be further from the truth. Most gas sensors are affected by cross interferences from vapors other than the target compound. Make sure you understand the effects of cross interfering gases on sensors and avoid misinterpreting the data they provide.

Weak internal standards. Don’t rely on manufacturers to set your policy standards. Equipment manufacturers are experts on their equipment. They are not experts in your field or operations. Make sure that your policies are driven by best practices in safety for your industry and not by what is most convenient or economically feasible. Simply relying on the “manufacturer’s recommendation” is no way to ensure that your program will protect people and property.

This article originally appeared in the October 2019 issue of Occupational Health & Safety.