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Confined Spaces: Myths, Magic, Urban Legends and the Facts

From labeling to atmospheric hazards to training, compliance with OSHA's confined space standard has proven to be a breeding ground for misunderstanding.

Much of the "popular" information circulating about confined spaces is simply wrong. Confined spaces don't have to be labeled. Oxygen levels of 19.5 percent aren't necessarily "safe" for entry. The mere possibility that an atmospheric hazard may exist doesn't necessarily mean that a confined space is a permit space. Showing employees a 20-minute video or sending them to a one-day, state-sponsored fire rescue institute seminar doesn't mean they have been trained.

Much of the truth underlying these myths can be found by carefully reading the OSHA standard, its preamble, the related compliance directive and the more than 80 formal letters of interpretation concerning confined spaces that the agency has issued over the last decade.

Myth: The OSHA standard requires you to prepare a written inventory of permit-required confined spaces.

Fact: Read 29 CFR 1910.146(c)(1). It only requires you to "... evaluate the workplace to determine if any spaces are permit-required confined spaces." While conducting an inventory is one way of doing this, it's not the only way. If you know your facility well enough, you might be able to make an evaluation without leaving your office. Don't believe me, look at the answer to the third question in Appendix E, section (c) of CPL 2.100.

Once you've identified your permit spaces, you must inform your employees about the existence of these spaces and of the hazards they pose. This leads to another confined space myth -- that permit spaces must be labeled.

Labeling Myth

Myth: The standard requires that permit-required confined spaces be labeled or posted.

Fact: If you read 29 CFR 1910.146(c)(2), you will see that the standard requires that employees be informed of the existence, location and danger posed by permit spaces" ... by posting danger signs or other equally effective means" [emphasis added] In other words, you can explain to people what a permit confined space is, tell them where they are in a facility and verbally warn them as to the hazards they present. If you're still a doubter, take a look at Federal Register, Vol. 58, No. 9, pages 4481-4484, and the answer to the fourth question in Appendix E, section (c) of CPL 2.100.

In some cases, posting may actually create another hazard. How can this be? I've seen lots of cases where someone has done a survey and determined at a particular point in time which spaces were permit spaces and which were not. Those that were, they posted, and those that weren't, they didn't.

When I'd ask what work was done in the space, they'd say something like inspection, removing materials or making mechanical adjustments. When I pressed further, they'd often point out that they might also use solvents in the space to clean or degrease parts.

What these folks failed to realize was that many confined spaces are not static environments. Things can change. In fact, they can change year to year, month to month, day to day and, in some cases, hour to hour or minute to minute.

Unfortunately, they failed to consider that job-related hazards, such as solvent vapors, could turn a nonpermit space into a permit space. If a space isn't posted as a permit space, workers who enter might not think that any special precautions or permits are necessary.

The whole purpose for posting permit spaces is to notify people who might not otherwise recognize them as permit spaces and enter them inadvertently. Moreover, in the standard's preamble, OSHA specifically points out that it does not " ... require the posting of any permit space whose only means of access necessitates the use of tools or keys, provided that the employees who are expected to gain entry into these spaces are trained to recognize the hazards involved. Restricting access to permit spaces in this manner protects employees effectively without the use of signs." (Federal Register, Vol. 58, No. 9, page 4484.)

The key thing to remember here is that employees must be informed of the hazards posed by confined spaces. If you want to label your spaces, you might want to consider labeling all of them. You might also want to consider adding an admonition to check with a designated authority before entering any of these spaces.

Atmospheric Hazard Myths

Myth: The atmosphere in a confined space can change in the blink of an eye.

Fact: The laws of chemistry and physics prohibit the atmosphere from changing instantaneously. For example, the oxygen content in a space won't be 20.8 percent one minute and 0 percent the next.

Yes, the atmosphere in a confined space can change, but it will always change at some rate. If the space is monitored continuously with an appropriately selected instrument that has been properly calibrated and set to alarm at a specified contaminant concentration, the alarm will sound when the contaminant level reaches that prescribed level, signaling the entrants that they need to evacuate.

Although it's unlikely that confined space atmospheres will change instantaneously, they can change over time. This is why past history of a space's atmosphere doesn't provide any indication of its present condition. Consequently, it's prudent to not only test confined spaces prior to entry, but also to provide continuous air monitoring when technology to provide such monitoring exists.

Myth: A confined space with an oxygen level of 19.5 percent is "safe" for entry.

Fact: A confined space with an atmosphere that contains 19.5 percent oxygen may be immediately dangerous to life or health (IDLH). The two principal ways in which an oxygen deficiency may arise in a confined space are displacement with inert gases such as argon, helium or nitrogen, and consumption by combustion or corrosion.

While a detailed discussion of why atmospheres of less than 19.5 percent oxygen are hazardous is beyond the scope of this article, additional information on this subject may be found in my article "Confined Spaces: Is 19.5 Percent Oxygen Really 'Safe'?" (OH, June 1999.) For our purposes, suffice it to say that an oxygen level of 19.5 percent means that there is approximately 7.5 percent, or 75,000 ppm, of something else inside the space. That may not be a significant problem if that 75,000 ppm is an inert gas such as nitrogen, argon or helium, but it's different if the contaminant is a solvent, such as n-hexane.

The ACGIH Threshold Limit Value (TLV) and IDLH value for n-hexane are 50 ppm and 1,100 ppm, respectively. So a space containing 75,000 ppm n-hexane would be 1,500 times over the TLV and 68 times over the IDLH level. Thus, even though the space contained 19.5 percent oxygen, it would clearly not be considered "safe" for entry.

Myth: A confined space with a flammable gas concentration less than 10 percent LFL is "safe" for entry.

Fact: If you read the definition for a "hazardous atmosphere" in 29 CFR 1910.146(b), you'll see that it doesn't say that atmospheres containing 10 percent LFL or less are "safe." It says that those containing more than 10 percent LFL are hazardous. For example, toluene has a LFL of 1.1 percent, or 11,000 ppm. Ten percent of the LFL is 1,100 ppm. While this atmosphere may be suitable for entry from a fire and explosion perspective, it's 20 times over toluene's TLV of 50 ppm and more than twice its IDLH level of 500 ppm.

Myth: A confined space with an atmosphere greater that 10 percent LFL cannot be entered.

Fact: In a letter of interpretation dated Sept. 4, 1996, to Macon Jones of Blasting Cleaning Products Ltd. in Oakville, Ontario, John B. Miles Jr., then OSHA's directorate of compliance programs, stated that "[t]he permit-required confined spaces standard (29 CFR 1910.146) does not prohibit working in a permit-required space where the atmosphere is above 10 percent of the LFL. Once the atmosphere is above 10 percent of the LFL, all of the requirements of the standard must be met." (Go to .)

In other words, spaces with atmospheres greater than 10 percent LFL may be entered, but only under the auspices of a comprehensive, written confined space program that meets all of the requirements outlined in 29 CFR 1910.146(d).

Myth: A concentration of atmospheric contaminants in excess of the OSHA PEL makes a confined space a permit-required space.

Fact: First of all, no self-respecting safety and health professional should even be relying on OSHA PELs. The PELs are based on the 1968 ACGIH TLVs, which are more than 30 years old. As a practical matter, the current TLVs are a more appropriate tool to use than OSHA's woefully outdated PELs.

Second, just because the atmosphere in a confined space is over the TLV doesn't necessarily mean that a confined space is a permit-required space. The footnote that accompanies the definition of a hazardous atmosphere in 29 CFR 1910.146(b) states that "... atmospheric concentrations of any substance that is not capable of causing death, incapacitation, impairment or ability to self-rescue, injury or acute illness due to its health effects is not covered by this provision" [emphasis added].

The TLVs for some chemicals are established because the substance is a nuisance at the TLV concentration, not because it poses an acute health hazard. Consequently, just because a contaminant level exceeds the TLV doesn't mean that a "hazardous atmosphere" is present. For a "hazardous atmosphere" to exist, the substance of interest must be one that poses acute health effects or that might impede an entrant's ability to escape in an emergency. Some materials, like asbestos and arsenic, don't meet that criteria; others, like most solvent vapors and gases such as H2S, SO2, Cl2, O3, COCl2, do.

Further guidance on this topic can be found in a letter of interpretation dated March 26, 1999, to Marc A. Viera of SAGE Environmental in Pawtucket, R.I. ( In that letter, Richard Fairfax, OSHA's director of compliance programs, wrote that "[t]he preamble to the Permit-Required Confined Space standard (Federal Register, Jan. 14, 1993, Vol. 58, No. 9, page 4474) clearly states that an atmosphere that contains a substance at a concentration exceeding a permissible exposure limit intended solely to prevent long-term adverse health effects is not considered to be a hazardous atmosphere on that basis alone. Therefore, if the atmosphere is above the PEL, then it would not automatically be classified as a "hazardous atmosphere."

Myth: The mere possibility that a "hazardous atmosphere" may exist in a confined space makes that space a permit-required space.

Fact: Wrong again. Practically speaking, it is the "likelihood," not the mere "possibility," that the hazard may exist that's important. To illustrate the difference between these two seemingly similar terms, consider the earth being hit by a meteor in the next hour. While such an event is "possible," it's not particularly "likely."

This issue was also addressed in a letter of interpretation dated Oct. 27, 1995, to James Sharpe of Consolidated Engineers Services in Arlington, Va. In that letter, OSHA's Miles responded to a question concerning whether certain crawl spaces could be considered permit spaces. He explained that the crawl spaces of "commercial building[s] generally contain utility service lines (i.e., water, natural gas, fuel oil, sewage, steam and electric power) that pass through them. If these utility services do not terminate at end use equipment in the crawl space, the inherent hazards of the material flowing through the service lines do not have to be considered in the permit-space determination unless there is reason to believe there is a reasonable probability of a rupture or leak where the contents of the piping would cause a serious safety or health hazard." (See .)

In other words, just because there's bad stuff flowing though a pipe that passes though a confined space doesn't necessarily make that space a permit space. Instead, one has to evaluate the "likelihood" of a release. If the pipe is in reasonably good condition, it is unlikely to fail catastrophically, short of being hit by a meteor. On the other hand, if it contains dispensing valves, the equation would change because such equipment can and does leak.

Instrumentation Myths

Myth: Confined space instruments should be calibrated in accordance with the manufacturer's recommendations.

Fact: Some manufacturer's instruction manuals recommend that instruments be calibrated every 30 days. By quizzing a product engineer who was exhibiting such an instrument at a professional conference, I determined that the 30-day recommendation for his instrument was based on its stability on a lab bench. Most people don't leave their instruments on a bench. They have them thumping around in the back of a pickup truck or knocking around an equipment storage locker.

A lot of things can happen when you jostle an instrument. A wire can break, a sensor can work loose, a trim pot can drift, and a circuit board can crack. Without checking the instrument prior to each use, there is no way to ensure that it is responding properly.

Myth: Instrument manufacturers wouldn't sell instruments that don't do what they say they will.

Fact: Some handheld monitors sold for evaluating confined space atmospheres are absolutely useless for that purpose. For example, the specifications in one manufacturer's instrument manual shows that the unit has a full-scale range of 0 to 1,000 ppm for carbon monoxide with an accuracy of +- 5 percent full scale.

Do the arithmetic yourself. Five percent of 1,000 ppm is 50 ppm. That means every reading taken with this instrument could be off by +- 50 ppm. Putting it a different way, a meter reading zero in an atmosphere containing 50 ppm of CO would be working in accordance with the manufacturer's published specifications even though the CO concentration would be twice the TLV of 25 ppm!

Construction Is Exempt

Myth: The construction industry is exempt from OSHA's confined space standard.

Fact. This myth stems from a misunderstanding of 29 CFR 1910.146(a) which states that "[t]his section does not apply to agriculture, to construction or to shipyard employment."

What some contractors don't seem to understand is that, while they may consider themselves part of the "construction industry," much of the work they do is not really construction, it's maintenance and repair. Moreover, OSHA has made it abundantly clear that maintenance and repair activities are covered by the general industry standard.

CPL 2.100 specifically states that "... permit-required confined spaces that are undergoing maintenance or modifications, which do not involve construction, are subject to the general industry standards." On the other hand, a confined space created during, or as a result of, construction activity or entered to perform construction activity would usually fall within the scope of the 29 CFR 1926 until the space is turned over for general industry operations.

For example, a new petroleum storage tank, chemical reactor or process vessel being built from scratch is covered by the construction standards until the entity for which it is being built takes possession. At that point, further entry into the spaces is covered by the general industry regulation.

The following examples, which are drawn directly from CPL 2.100, clearly illustrate the difference between construction and maintenance:

  • Lining a tank that is in need of restoration to prevent the structural part of the tank from deteriorating or to prevent the product from being contaminated by the material making up the tank structure. In either case, the partial patching or total removal of existing lining and replacement is maintenance. The installation of a new lining for the above reasons is also maintenance.
  • Relining of a furnace with new refractory material is maintenance.
  • Tuck pointing and individual brick replacement in a manhole is maintenance.
  • Relining of a sewer line using a sleeve pushed through a section of the existing system is maintenance.
  • Repainting, which is part of a scheduled program to maintain a system or prevent its deterioration, is maintenance.

The important thing to realize is that it's the nature of the work, not the nature of the employer that determines coverage under the standard. Note too that 29 CFR 1910.146(a) doesn't say that the construction industry is exempt from coverage. It says that the standard does not apply to construction employment.

As a practical matter, it doesn't really make any difference whether contractors are legally covered by OSHA's permit-required confined space regulation because they still need to take a variety of precautions when entering permit-required confined spaces.

Specifically, the agency's enforcement policy stipulates that contractors not covered by the general industry regulations must comply with American National Standards Institute (ANSI) Standard Z-117.1, Safety Requirements for Confined Spaces. Not surprisingly, ANSI's requirements closely parallel those in 29 CFR 1910.146.

In a letter of interpretation dated Jan. 27, 1994, ( to Bruce Smith of Speed Shore Corp. of Houston, Roy F. Gurnham, then OSHA's director of the Office of Construction and Maritime Compliance Assistance, explained:

"OSHA's enforcement policy with regard to confined spaces at construction sites has not changed with the promulgation of the general industry regulation. In those instances where a hazard is addressed by an existing part of the 1926 standard, OSHA will continue to cite the specific standard. In those cases where a hazard is observed that is not addressed by an existing specific construction standard but is addressed in the American National Standards Institute's Z117.1 consensus standard, OSHA will continue to cite under 5(a)(1) of the Act, provided the conditions for citing the general duty clause are present."

The SCBA Cylinder Myth

Myth. It's OK to remove SCBA cylinders from your back to get through small manholes.

Fact: OSHA standard 29 CFR 1910.134(d)(1)(ii) states that every "respirator shall be used in compliance with the conditions of its certification." When NIOSH certifies SCBAs, it does so with the understanding that the air cylinders will be worn on employees' backs. The minute a user removes the cylinder to pass it through a narrow manway, the NIOSH certification is voided, and a violation of 29 CFR 1910.134(d)(1)(ii) exists.

Other Serious Hazards

Myth. Slip, trip and fall hazards that may exist in a confined space make that space a permit-required space.

Fact: This myth stems from 29 CFR 1910.146(b) that says that a confined space that "[c]ontains any other recognized serious safety or health hazard" is a permit-required space. The question, then, is what exactly constitutes a "serious hazard?"

An answer to this question may be found directly in the Occupational Safety and Health (OSH) Act. Section 17(k) of the OSH Act says that a violation is serious if there is "... substantial probability that death or serious physical harm could result from a condition that exists, or from one or more practices, means, methods, operations or processes that have been adopted or are in use ... ."

It's important to understand this definition to properly classify confined spaces. For example, just because someone can fall off a ladder in a confined space doesn't necessarily make that space a permit space. Yes, falls from elevations can lead to death or serious physical harm, but an OSHA policy considers this to be a walking-working surface issue that is better addressed by other standards.

In his Feb. 23, 1999, memorandum, Herbert Washington, director of OSHA's Office of General Industry Compliance Assistance, sheds further light on this issue. In answering the hypothetical question "Would a pit that meets the definition as a confined space also meet the definition of a permit-required confined space [PRCS] if the only hazard is a potential fall from 21 feet while descending on a ladder within the pit?", Washington wrote:

"Specific fall protection requirements were not included in the PRCS standard. Fall protection and ladder safety requirements are addressed in Walking-Working Surfaces, 29 CFR 1910, Subpart D and the general-duty clause of the Occupational Safety and Health Act. Therefore, if the described potential fall hazard is the exclusive hazard within this pit, a permit program would not be required."

Training Myths

Myths: Showing employees videotapes or letting them use interactive computer or Web-based instruction meets OSHA's requirements for confined space training.

Fact: Regardless of the advertising hype you may see or hear, watching a videotape or spending a few hours in front of a computer isn't sufficient to meet the regulation's training requirements. A variety of letters of interpretation from OSHA's national office make it abundantly clear that, although video tapes and computerized courses may be used as part of a training program, simply showing employees these materials does not meet the training requirements imposed by the confined space rule. Don't believe me, check out these letters yourself:

Think about it. There isn't a department of motor vehicles in the country that will let someone get behind the wheel of a car and drive away after watching a 20-minute videotape or completing an interactive, computer-based training program. Because confined space entry demands far more knowledge and skill than driving a car, how can anyone believe that workers would be trained on such a complex topic after watching a videotape or completing an interactive computer program?

We Weren't Cited by OSHA

Myth: We didn't get cited by OSHA, so our program must be OK.

Fact: First, this presumes that the inspector even evaluated your program. If the scope of inspection was limited, as it often is with accident or complaint investigations, the inspector may not have even reviewed your program.

Second, even if an inspector did look at it, the fact that no citations were issued doesn't mean you're in compliance. How can this be? As I'll explain in another article later in the year, it is possible that the inspector who visited your plant didn't have the background, experience, knowledge or skills necessary to evaluate your program.

Confined space entry is perhaps the most complex area in the whole field of occupational safety and health because it requires not just knowledge, but expert technical knowledge of a broad spectrum of specialized areas such as process hazard analysis, air sampling methodology, lockout/tagout, toxicology, respiratory protection, industrial ventilation, chemical protective clothing, emergency planning, instrumentation and employee training.

Inspector turnover in some offices is so high that you might be inspected by someone with very little knowledge or experience. In some cases, people whose facilities are being inspected know more about OSHA's history, operations, policies, procedures and standards than the person inspecting them. That's a topic for another story.

In the case of confined spaces, many untruths, myths and urban legends are repeated so often that people eventually believe them. Even worse, they pass them on to others.

I encourage participants in all of my seminars to be suspicious, to question authority, to ask why and, when possible, to do their own research, because what everybody knows to be true is often wrong.

Contributing Editor John F. Rekus, MS, CIH, CSP, is an independent consultant and author of the Complete Confined Spaces Handbook. With more than 20 years of regulatory experience, he conducts OSHA compliance surveys and provides exciting, dynamic and action-packed educational seminars for workers, managers, corporations and trade associations. He lives in Baltimore and may be reached at (410) 583-7954. Visit his Web site at .

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