Confined Space Entry Training

OSHA Confined Space Entry Training and Certification

Definition of a Hazardous Atmosphere – Toxic Substance Exceeding the OSHA PEL

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OSHA Hazardous Atmosphere Toxic PEL

Blog Post #12 – In this post to The Confined Space Training Blog, we will examine the fourth category listed in the Federal OSHA definition for a hazardous atmosphere, which is an atmosphere that contains any toxic substance present in quantity greater than its permissible exposure limit, or PEL.

Before moving on, make certain to pay close attention to an important footnote to this definition in the OSHA definition section for this standard. OSHA states that this category of hazardous atmosphere only applies “if the topic substance can cause death, incapacitation, impairment in ability to self-rescue, injury, or acute illness due to its health effects.”

For example, exposure to ammonia in the atmosphere at levels above its PEL for an extended period of time would cause the entrant to experience burning eyes and throat, difficulty breathing, and make it extremely difficult to function normally; exposure to extremely high levels could even lead to death. This condition would meet the definition of a hazardous toxic atmosphere in the confined space standards. However, exposure to silica or asbestos at levels over their respective PELs, although harmful in the long term, would typically not cause any immediate reaction. So, overexposure to those particular substances would not meet the definition of a hazardous atmosphere as defined in the OSHA confined space standard (although normal protective measures required by other OSHA standards would still be applicable).

What are OSHA PELs?

The term PEL represents the maximum exposure level for a particular contaminant that an employee may be exposed to at work, averaged over a specified period of time, without suffering negative health effects or needing to take protective measures such as use of a respirator. PELs for various contaminants are established by Federal OSHA and are listed in different parts of the OSHA code of federal regulations.

Part 1910 lists the PELs that apply to general industry worksites. Part 1926 for construction and Part 1915 for shipyards also have PELs, and some of those may differ from those listed in Part 1910. In addition, many states operate their own OSHA approved state program. Some have adopted the federal OSHA PELs, but a few states have established their own PELs, some which are lower than federal OSHA’s.

In addition to the mandatory OSHA PELs, there are some other voluntary limits that you may hear mentioned. For example, The American Conference of Governmental Industrial Hygienists, or ACGIH, has developed threshold limit values, or TLVs, for many substances. And The National Institutes of Occupational Safety and Health, or NIOSH, developed recommended exposure limits, or RELs, for many substances. These are based on more recent research than the OSHA PELs in many cases, and may be set lower (or higher) than the OSHA PEL for some substances.  Employers MAY voluntarily choose to utilize these lower limits instead. Also, these voluntary limits are often utilized when OSHA has not established a mandatory PEL for a specific substance.

The permissible exposure limits for most individual substances in gas and vapor form are presented as parts per million, or PPM, which is a way to measure very small quantities of toxic air contaminants at a molecular level. The more toxic the substance, the lower the PEL. For example, the 1910 General Industry permissible exposure limit for ammonia is 50 ppm.

To help visualize the concept of substances being measured in parts per million, or ppm, consider this; if a contaminant evenly dispersed in a space makes up one half of the total atmosphere in that space, it would be measured at 500,000 ppm. If the substance made up 5% of the total atmosphere, it would be measured at 50,000 ppm, and if a substance made up 1% of the total atmosphere, it would measure at 10,000 ppm. A substance making up one tenth of 1% of the total atmosphere would measure at 1,000 ppm, and a substance making up one one-hundred-thousandth of a percent would be measured at 10 ppm. And a few substances are so toxic, their permissible exposure limits are actually measured in parts per billion, or PPB.      

The table below shows the federal OSHA PELs for a few common toxic substances found in some confined spaces.

OSHA Permissible Exposure Limits Confined Spaces

Different Types of OSHA PELs

Unless noted otherwise, OSHA permissible exposure limits are based on an “eight-hour time-weighted average,” also known as TWA.  8-hour TWA means that the employee exposure to the substance is averaged over an eight-hour work shift. For example, the OSHA PEL for acetone is listed as 1,000 ppm, which is averaged over 8 hours.

Some permissible exposure limits are appended with a designation of ST or STEL, which stands for “short term exposure limit.” This is an exposure limit that is averaged over a shorter, 15-minute time period, as opposed to the 8-hour period. For example, the PELs for benzene are listed as 1 ppm based on an 8-hour TWA, but a STEL of only 5 ppm.

A few other substances are marked with the letter C, which stands for ceiling limit. For example, the PEL for chlorine is a ceiling limit of only 1 ppm. This limit is instantly reached any time the employee is exposed to the substance at the level specified.

It is important for employers to identify the toxic substances that employees may be exposed to when entering confined spaces. It is also important for entrants and attendants to know about the modes of exposure, as well as the signs and symptoms of overexposure, to toxic substances. This information can usually be obtained from each substance’s safety data sheet, or SDS.

Toxic Atmospheres in Confined Spaces

So, in review, a hazardous atmosphere exists where a toxic substance is present in a quantity greater than its permissible exposure limit (PEL). This can occur in confined spaces such as, but not limited to, tanks and vessels where a toxic product has been stored or is being utilized, and in underground spaces, such as crawl spaces, utility vaults and sewers, where a hazardous substance such as hydrogen sulfide (H2S) can migrate into the space.

Also, toxic gases such as CO can be created by equipment such as generators, chop saws, and compactors that are powered by internal combustion engines. As a reminder, if there is a hazardous substance for which OSHA has not established a PEL, refer to that substance’s safety data sheet, or SDS, for exposure recommendations and guidelines.

In our next blog post (#13), we will examine the fifth and final criteria of a hazardous atmosphere that could be present inside of a confined space (any other IDLH atmosphere). In the meantime, please provide your feedback to this blog post about toxic atmospheres in the comments section below.

And as always, I hope you will take a moment to spread the word about our confined space training blog by sharing a link to this post with others in your network so they can benefit from this information. Thanks – Curtis

Definition of a Hazardous Atmosphere – Oxygen Deficiency or Enrichment

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Oxygen deficient atmosphere

Blog Post #11 – In this post to The Confined Space Training Blog, we will examine the third category listed in the Federal OSHA definition for a hazardous atmosphere, which is an atmospheric concentration of oxygen less than 19.5%, or greater than 23.5%.

Atmospheric Composition

Oxygen is critical to support human life. However, under normal conditions, over 78 percent of the air we breathe is actually comprised of nitrogen, which is an inert gas. And oxygen, commonly referred to as O2, makes up approximately 20.9% of the atmosphere.

OSHA hazardous atmosphere oxygen enrichment or oxygen deficiency

If oxygen levels were to fluctuate slightly, there would most likely be no ill effects on a healthy person. However, a greater decrease or increase in oxygen levels could prove to be harmful; even deadly.

So, OSHA sets the threshold for an oxygen deficient atmosphere at anything less than 19.5% oxygen, and the threshold for an oxygen enriched atmosphere is reached when the O2 levels exceed 23.5%.

What Can Cause an Oxygen Deficient Atmosphere?

One way an atmosphere may become oxygen deficient is if the oxygen gets consumed. One cause of oxygen consumption is flames. A flame must have adequate oxygen to burn. As the flame burns, the oxygen is consumed. That is why the flame on a small candle will slowly extinguish if you cover the candle with a glass, preventing it from getting more oxygen. Similarly, a poorly ventilated confined space in which there has been a flash fire, or where flame producing equipment is present, could become oxygen deficient.

Oxidation is another cause of oxygen deficiency. When metal rusts, that process, called oxidation, consumes oxygen. So does the process of concrete curing. Therefore, confined spaces with a rusty interior surface, or confined spaces formed with freshly poured concrete, could also become oxygen deficient over time.

An oxygen deficient atmosphere can also be created by displacement of the atmosphere, which can occur if another gas fills up the confined space and supplants the oxygen. This happens inside sewers and underground vaults quite often, when naturally-occurring Methane gas seeps into the space. Another way for this to occur is when another gas is accidentally introduced into a confined space through a leaking pipe, cracked hose, or partially open valve. For example, a leaking hose containing Argon or other inert shield gases used during some welding processes is one potential cause of oxygen displacement inside a confined space.

In relatively rare cases, an inert gas is introduced into a confined space purposely, to displace oxygen. This can help prevent materials inside the space from oxidizing. Purging the space with an inert gas can also prevent a highly-flammable atmosphere from igniting during entry operations.

Another way oxygen can be displaced is when certain chemicals are mixed inside of a confined space. For example, mixing vinegar and baking soda creates a bubbly concoction that releases carbon dioxide gas when the bubbles burst. When these or other reactive chemicals are present in great enough quantities, the resulting chemical reactions could release gases that eventually build up to levels high enough to displace oxygen in the confined space.

A less common cause of oxygen deficiency is adsorption. Some manufacturing processes utilize activated charcoal filters to capture unwanted gases. Sometimes a portion of the oxygen adheres to the activated charcoal, which can result in lower oxygen levels in the air.

Effects of Oxygen Deficiency

The effects of oxygen deficiency on a person vary as the level of oxygen drops. In reality, most people in good health would probably not perceive much, if any, ill effect when oxygen levels drop to 19.5%, the threshold of oxygen deficiency. However, when oxygen levels drop to around 16%, the entrant may start suffering the symptoms of hypoxia, where they find it harder to breathe and start to become nauseous and drowsy. When oxygen levels drop to 12% or less, the entrant will become unconscious, and when oxygen levels drop to 6% or less, brain cells begin to deteriorate, and death occurs through asphyxiation.

What is an Oxygen Enriched Atmosphere?

When oxygen levels inside a confined space exceed 23.5% by volume, an oxygen enriched atmosphere is present. One common reason this occurs is because pure oxygen is introduced into the space, either accidentally or on purpose.

Leaking hoses, pipes, or valves on equipment that utilize pure oxygen can result in an oxygen enriched atmosphere inside a confined space. That is why the OSHA welding and cutting standards require an oxy-fuel cutting torch be removed from inside a tank or other enclosed space when not in use.

In other cases, pure oxygen is used to ventilate a confined space with an oxygen deficient atmosphere. This should never be done, as the result can be the introduction of too much oxygen into the confined space. To control an oxygen deficient confined space, blow fresh air into the space using a ventilation fan or blower stationed outside the space. And never place oxygen cylinders, or any other gas cylinders, inside of a confined space, as their contents could leak into the space and adversely affect oxygen levels.

Effects of Oxygen Enrichment

So, why is too much oxygen a bad thing? Primarily, it is because oxygen accelerates the combustion process. In an oxygen enriched atmosphere, the oxygen can saturate the worker’s clothing or other combustible materials inside the space. Then, a single spark from a grinder, torch, or even static electricity can ignite the oxygen-saturated items, which will cause them to burn rapidly.

OSHA Requirements for Oxygen Levels in a Confined Space

In review, an oxygen deficient atmosphere occurs when oxygen levels drop below 19.5% of the atmosphere by volume, and an oxygen enriched atmosphere occurs when oxygen levels exceed 23.5% of the atmosphere by volume.

Oxygen deficiency can occur in many confined spaces, including, but not limited to, tanks and similar vessels that have contained a product whose vapors could displace the oxygen, or that are subject to having the inside purged with an inert gas such as nitrogen. These conditions could also occur inside sewers and underground utility vaults where methane or other naturally occurring gases could collect and displace the oxygen. And oxygen enrichment can occur inside confined spaces into which oxygen accidentally leaks, or where it is introduced into the space on purpose.

In our next blog post (#12), we will examine the fourth criteria of a hazardous atmosphere that could be present inside of a confined space (a toxic atmosphere). In the meantime, please provide your feedback to this blog post about oxygen deficient and oxygen enriched atmospheres in the comments section below.

And as always, I hope you will take a moment to spread the word about our confined space training blog by sharing a link to this post with others in your network so they can benefit from this information. Thanks – Curtis

Definition of a Hazardous Atmosphere – Flammable Gas, Vapor or Mist >10% LFL

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Hazardous atmosphere flammable gas vapor or mist greater than 10% LFL or LEL

 Blog Post #9 – In previous blog posts, we discussed how to identify confined spaces, and provided several examples of such spaces. Next we will examine the factors that determine whether or not each confined space identified at your workplace must be classified as a permit-required confined space, starting with a hazardous atmosphere that contains a flammable gas, vapor, or mist in excess of 10% of its lower flammable limit, or LFL.

 OSHA Definition of a Permit-required Confined Space

The Federal OSHA definition of a permit-required confined space for general industry can be found in 1910.146, paragraph B, titled definitions, and in 1926.1202, also titled definitions, for the construction industry. That is where OSHA lists the four types of hazards that require a confined space be classified as a permit required confined space. Those four types of hazards are:

  • The space contains an actual or potential hazardous atmosphere;

  • The space contains a material with the potential to engulf the entrant;

  • The space is configured to trap or asphyxiate the entrant; or;

  • The space contains some other recognized serious safety or health hazard.

 What is a Hazardous Atmosphere?

 The Federal OSHA definition for “hazardous atmosphere”, the first classification listed above, is also found in 1910.146, paragraph B, definitions, for general industry, and in 1926.1202, definitions, for the construction industry.

There are five different types, or classifications, of hazardous atmospheres, listed in these two OSHA definitions. Those classifications, which are nearly identical in the two standards, are:

 (1) – Flammable gas, vapor, or mist in excess of 10 percent of its lower flammable limit (LFL);

 (2) – Airborne combustible dust at a concentration that meets or exceeds its LFL;

 (3) – Atmospheric oxygen concentration below 19.5 percent or above 23.5 percent;

 (4) – Atmospheric concentration of any substance for which a dose or a permissible exposure limit is published in subpart G, Occupational Health and Environmental Control, or in subpart Z, Toxic and Hazardous Substances, of this part and which could result in employee exposure in excess of its dose or permissible exposure limit;

 (5) – Any other atmospheric condition that is immediately dangerous to life or health.

 The balance of this particular blog post focuses on the first category of a hazardous atmosphere listed above, which is a flammable gas, vapor, or mist greater than 10% of its lower flammable

Greater Than 10 Percent Lower Flammable Limit (LFL)

 OSHA includes this type hazard because they do not want employers to wait until conditions are ripe for a flash fire or explosion to occur inside of a confined space before taking precautionary measures. Atmospheric conditions inside a confined space that contain a low level of flammable gas, vapor, or mist could quickly change for the worse. Therefore, OSHA regulations classify a flammable gas, mist, or vapor present inside a confined space at levels over 10% of its LFL as a hazardous atmosphere. Once that level is reached inside a confined space, or if there is a reasonable probability that it will develop within the space during entry operations, that space must be classified as a permit-required confined space.

 Lower Flammable Limit (LFL) Explained

 So, what is LFL? It stands for Lower Flammable Limit. The LFL is the minimum amount of a particular flammable gas, vapor, or mist that must be present in the atmosphere to ignite and burn. If you introduce an extremely small amount of a flammable gas, vapor, or mist into the atmosphere of a confined space, it might not ignite when exposed to an ignition source (such as a spark or flame) because there is not enough of the material present to form a flammable mixture in the air. How much flammable gas, vapor, or mist is needed in the atmosphere for a fire or explosion to occur? That depends on the gas, vapor, or mist present inside either space, as they all have a different LFL.

 What is LEL?

Be aware the term “LFL” is also referred to as “LEL”, or Lower Explosive Limit. The terms LFL and LEL are basically interchangeable. While OSHA uses LFL in their confined space standards, LEL is commonly used by many gas detection equipment manufacturers, as well as in many written confined space entry programs. Also, I may on occasion use the term LEL throughout future blog posts.

 LFLs of Common Flammable Gasses

The LELs of a few common combustible materials are listed in the chart below. An LEL is expressed as a percentage of the atmosphere within the confined space that is comprised of a particular combustible gas, vapor, or mist. For example, the LEL of Methane gas, with the chemical identifier of CH4, is 5% of the atmosphere at any given point. As you can see, the LELs of various gases differ quite a bit. 

Upper and lower flammable limits of common gasses

What does UFL mean?

Note that each of the combustible materials listed in the chart also have their own UFL, or Upper Flammable Limit (expressed in the chart as an UEL). If a flammable gas, vapor, or mist is present in the atmosphere in quantities greater than its UFL, it will not ignite and burn. I bring up this term because while OSHA does not regulate UFLs, they do come into play when we discuss gas detection equipment in later blog posts.

Flammability Characteristics of Methane Gas

As mentioned earlier, the LFL of Methane gas is 5%. So, if Methane gas is present in a confined space, but it does not make up at least 5% of the atmosphere at any point within the space, there will be no flash fire or explosion if there is a spark or other source of ignition. And the upper flammable limit, or UFL, of Methane gas is 15%; So, a confined space containing higher levels of Methane would not burn or explode either. However, if the amount of Methane gas increases or decreases to fall somewhere between its LFL and UFL at any point inside a confined space and there is any source of ignition in that same area, a fire or explosion will occur.

Since Methane gas has an LFL of 5% of the atmosphere, a hazardous atmosphere as defined by OSHA would be present inside a confined space if the amount of Methane gas in the atmosphere exceeds 10% of that level. The presence of that level of Methane gas, which equates to just 0.5% of the total atmosphere, means the space would have to be classified as a permit-required confined space.

Other Hazards Associated with Methane Gas

Before moving on, let’s take a moment to discuss Methane gas, or CH4, a little more, as this is a hazardous gas commonly found in a variety of confined spaces. Methane is a colorless, tasteless gas that has no odor, so its presence cannot be detected by your senses alone. But too much Methane gas inside of a confined space creates not only a potentially flammable atmosphere, as previously discussed, it can also displace oxygen in the space, creating a deficiency of oxygen for an entrant to breathe. Fortunately, while Methane is a highly flammable gas that can also displace oxygen, it is one of the few flammable gases that is not toxic.

Where is Methane Gas Commonly Found?

Methane is created when organic matter decomposes. Therefore, it is commonly found in potentially harmful quantities within confined spaces such as sewers and related facilities, manure pits, and in silos that have held grain or similar materials that has rotted. Methane is also commonly found in confined spaces such as underground utility vaults, especially those located near landfills (the rotting trash creates Methane). Therefore, these spaces are typically classified as permit-required confined spaces.

More Examples of Confined Spaces With Potentially Flammable Atmospheres

Other examples of confined spaces with a reasonable potential to contain an atmosphere containing a flammable gas, vapor, or mist above 10% of its LFL include pipelines, tanks and other vessels that have contained fuels or other flammable or combustible materials, even when they have been emptied of their contents. Also, confined spaces where work processes such as cutting with an oxy-acetylene torch or painting with flammable paints and solvents is taking place inside could potentially contain a hazardous atmosphere. And confined spaces such as vaults or tunnels in which there are leaking valves or piping used to transport flammable gas could also contain a hazardous atmosphere. As such, each of these spaces would also likely be classified as a permit-required confined space.

So, in review, any confined space with an actual flammable gas, vapor, or mist present at levels greater than 10 percent of its lower flammable limit, or LFL, is considered to have a hazardous atmosphere. And that means the space must be classified as a permit-required confined space. The same is true for any confined space in which that level of a flammable atmosphere could reasonably be expected to develop during entry operations. You may also hear the term LEL, which stands for lower explosive level, being used to describe a hazardous flammable atmosphere inside a confined space, as that term is synonymous with LFL.

In our next blog post (#10), we will examine the second criteria of a hazardous atmosphere that could be present inside of a confined space (combustible dust). In the meantime, please provide your feedback and questions to this blog post in the comments section below. And as always, I urge you to share a link to this confined space training blog post with anyone in your network who could benefit from this information. Thanks – Curtis