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29 June 2017

Confined Spaces in Construction and Atmospheric Testing


In 1993, 29 CFR 1910.146 went into effect as the first federal legislation governing entry into permit-required confined spaces in general industry. Because some industries, such as the construction industry, were covered by specific Occupational Safety and Health Administration (OSHA) safety regulations, they were exempt from the confined space entry requirements of the general industry rule. The construction standard, 29 CFR 1926, did not cover confined space entry as reflected in 2005-2009 statistics where 61% of all confined space fatalities occurred during construction, repairing, or cleaning activities.1 As such, OSHA introduced 29 CFR 1926, Subpart AA, the final rules governing entry into permit-required confined spaces for the construction industry on May 4, 2015.

This paper will not define what constitutes a confined space, permit required or otherwise, and will not attempt to determine what is and is not considered construction, but will focus on the requirements and best practices of atmospheric testing during confined space entry procedures.







Atmospheric testing plays an important role in the 2015 regulation. Like the general industry standard, the construction safety standard requires testing of the atmosphere and verification that it is safe prior to anyone entering the confined space. Specially the standard states:

Before an employee enters the space, the internal atmosphere must be tested, with a calibrated direct-reading instrument, for oxygen content, for flammable gases and vapours, and for potential toxic air contaminants, in that order. Any employee who enters the space, or that employee’s authorised representative, must be provided an opportunity to observe the pre-entry testing required by this paragraph.²

Testing the atmosphere before an employee enters the space means that you must sample the atmosphere within the space from outside the point of entry or from some other access point outside of the space. This testing requires that the monitor is equipped with a sampling pump and a sample of the atmosphere in the space is drawn to the monitor. This must be done regardless of whether the access or entry to the space is vertical or horizontal in nature. The monitor may have an integral pump, it may use a detachable pump, or it may use a simple hand-aspirated pump. The conjuration of the pump itself is less important; the nature of the confined space and the confined space program should dictate which type of pump is best to use. If the space requires a vertical entry or vertical access point, a flexible sample hose with enough length to reach the bottom of the space should be attached to the pump. If the space requires a horizontal entry, a rigid probe should be attached to the pump and used to sample the atmosphere inside the space.

The standard requires that the atmosphere is tested with a “calibrated” instrument. Unfortunately, the term “calibrated” is not otherwise de ned and there are no specific requirements stating the frequency or currency of the calibration. Calibration establishes the accuracy of the gas monitor used for testing by adjusting its readings to a set of known standard gas concentrations. The sensor outputs will drift and degrade with time and will be affected by changes in environmental conditions and the physical condition of the monitor. Routine calibration must be performed to maintain accuracy of the monitor over time. Most interpretations of the standard agree that “calibrated” means the gas monitor is calibrated in accordance with manufacturer recommendations. Calibration might appear to be a technically difficult operation, but most manufacturers provide equipment to automate the process.

As indicated in the standard above, the order of testing is important. Although it is most practical that all of these potential hazards are typically tested for simultaneously, it is the order of recognition of the hazard that is the key. A lack of oxygen is the most common atmospheric hazard encountered in a confined space and accounts for many confined space gas- related injuries and fatalities. For that reason, it makes sense to verify the oxygen concentration first. The oxygen concentration also gives insight into the validity of any combustible gas readings. If the oxygen concentration is too low, the combustible gas concentration could be much higher than indicated, leaving a potentially explosive atmosphere undetected. This does not mean the potential toxic hazards are a lesser consideration. The order of testing simply ensures that the most commonly acute hazards are recognised and mitigated first.

Under the general industry standard, it was common to perform a pre-entry atmospheric test, complete the permit, and put the gas monitor away until the next con ned space entry. Recognising that the levels of atmospheric hazards can change dramatically over time, or that the work being performed in the con ned space may introduce additional hazards, the construction standard has much stronger language with regard to continuously monitoring the atmosphere.

The atmosphere within the space must be continuously monitored unless the entry employer can demonstrate that equipment for continuous monitoring is not commercially available or periodic monitoring is sufficient. If continuous monitoring is used, the employer must ensure that the monitoring equipment has an alarm that will notify all entrants if a specified atmospheric threshold is achieved, or that an employee will check the monitor with sufficient frequency to ensure that entrants have adequate time to escape. If continuous monitoring is not used, periodic monitoring is required. All monitoring must ensure that the continuous forced air ventilation is preventing the accumulation of a hazardous atmosphere. Any employee who enters the space, or that employee’s authorised representative, must be provided with an opportunity to observe the testing required by this paragraph.3


The equipment for continuously monitoring the atmosphere in a confined space is available on the commercial market. In most cases it is the same or similar to the equipment used to complete the pre-entry testing. Arguably, the best way to accomplish continuously monitoring the atmosphere inside the space is to remove the sampling pump from the pre-entry monitor, clip it on the entrant, and have the entrant carry it into the space. Carrying or wearing the monitor ensures the entrants are properly noticed by any alarm conditions. With those alarm thresholds properly set, the entrants have more than adequate time to escape if the atmosphere starts to become hazardous. If there are multiple entrants in the space, providing each one with a monitor would offer the best protection and offer the best opportunity for the entrant to observe the testing required by the standard.








Every atmospheric testing program associated with confined space entry is filled with a number of 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 performing the work. Too often, this distraction from the organisation’s main theme causes the program to concentrate on doing only what is necessary to comply with the rules rather than focus on what is involved with the best practices in the industry. Chapter 7 of the National Fire “Carrying or wearing the monitor ensures that the entrants are properly noticed by any alarm conditions.”

Confined Spaces in Construction and Atmospheric Testing Protection Agency’s Guide for Safe Confined Space Entry and Work (NFPA 350) provides best practice guidelines for atmospheric testing in confined space entry procedures. Following those guidelines will help you avoid some of the common pitfalls listed below associated with atmospheric testing of confined spaces.





1. Wrong sensors for the job

– The most fundamental mistake in an air monitoring program is the lack of proper detection equipment. Somewhere along the way, a portable confined space gas monitor became de ned as a four- gas instrument which detects oxygen, combustible gas, carbon monoxide and hydrogen sulfide. While two of those components, oxygen and combustible gas sensors, are a must in almost every confined space application, the other two are not. Confined spaces are 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 essential to the success of the program.

2. 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 lead to damaged equipment and repairs that exceeds the cost of the device.

3. Bad zero references

– It’s natural to get to the job, turn your monitor on, look at the readings, and initiate a zeroing function. This is often done without knowing whether or not the atmosphere you are standing in at the time is suitable for establishing a proper zero reference on the instrument. You must be certain that the environment you are in is free of gas contaminants before zeroing. A clear indicator that you missed this step will be that the instrument displays 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 that this mistake has been made.

4. Improper calibration

– An instrument will only be 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 discuss further here.

5. Failure to test the equipment before use

– The only way to be certain that your instrument detects gas is to check it with gas before you use it. Performing a functional test on a gas monitor is a simple task which takes only a few seconds. Why would you trust your life to a piece of equipment which you can only assume is functioning properly? Would you be comfortable stepping on board 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.

6. No correlation between oxygen and combustible gas readings

– It is often overlooked that sensors used to detect combustible gases in most portable gas monitoring instruments rely on the presence of oxygen to provide an accurate reading. If the oxygen concentration in an environment is below 10%, a dangerous condition may go undetected because the combustible sensor will not function properly. 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.

7. Test it and forget it

– As discussed previously, 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 no indication that it will be safe 15, 30 or 60 minutes from now. The new regulations require continuously monitoring the atmosphere to make certain that it stays safe. Keep the instrument out and continue monitoring the atmosphere as long as the work continues.

8. Lack of training

– Workers are often handed an instrument, assigned the task of performing the atmospheric testing, 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, on-line tutorials, and personalised seminars are all readily available to help convey the knowledge and competency necessary for using gas-monitoring instruments. Don’t go to work without having a clear understanding of the equipment and how to use it properly.

9. 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 vapours other than the target compound. Make sure you understand the effects of cross interfering gases on sensors and avoid misinterpreting the data they provide.

10. Weak internal standards

– Don’t rely on equipment manufacturers to set your policy standards. Equipment manufacturers are experts on their equipment. They are not, nor do they claim to be in most cases, experts in your eld or operations. Make certain that your policies are driven by best safety practices 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 is built on the foundation of observing best practices whenever possible.

These are only a few of the common mistakes made in air monitoring programs throughout industry. If you pay attention to these factors you will be well on the way to ensuring that you comply with the applicable rules and that your gas monitoring program is following the best known practices in the eld.


The new standard for con ned space entry in the construction industry discussed above takes effect on August 3, 2015. How ready is your organisation to take on the new rules? Have you de ned your potential hazards? Do you have the gas monitoring equipment necessary to perform pre-entry testing and continuous monitoring as required by the regulation? Gas detection equipment manufacturers such as Industrial Scientific Corporation can provide a complete solution for atmospheric testing in confined spaces. Confined Space Kits are available to give you all of the equipment necessary to test and evaluate the air within a confined space including the gas monitor, sample pump, sample tubing, calibration gas and the regulator for the gas cylinder. If your work is unpredictable and your need for monitoring equipment is sporadic, there are rental programs to help you get what you need, when you need it, without the hassle of owning your own set of tools. If your confined space program is large and maintaining your own equipment will be an issue, there are plans available such as Industrial Scientific’s iNet program that will manage and maintain your fleet while you focus on your everyday work.

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