Ventilating a confined space isn't just about flipping on a fan and calling it a day. There’s an art—and a bit of science—to getting it right. If you don’t, you could be putting yourself and your team at risk. Let's break down four common mistakes people make when ventilating confined spaces: short-circuiting, recirculation, inadequate CFM, and bending ductwork like it’s a contortionist’s routine.

1. Short Circuiting

We’re not talking about blowing a fuse here—this short circuit is all about airflow. Picture this: you set up your ventilation to push fresh air into a confined space, but instead of circulating throughout the area, the air takes a shortcut right out of the portal. The result? Only a fraction of the space is getting ventilated, potentially leaving atmospheric contaminants in the space or workers’ breathing zone.

To avoid this, don’t just place your ventilation gear down and hope for the best. position the intake and exhaust strategically—ideally, on opposite ends of the space. Make sure that fresh air travels through the entire space, hitting every nook and cranny, before it exits. If the space in question only has a single portal, ensure that the ductwork is long enough and configured in a way that allows for ventilation in the area that work is taking place. On a side note, longer ductwork can result in decreased overall CFM – check with your manufacturer for details.

Recirculating air might be great for your car’s A/C, but in confined spaces, it can be a fatal mistake. If the air you’re pulling out of the space ends up getting sucked back in, you’re just circulating the same contaminated air over and over again. While the space may feel like it is being ventilated, the contaminates never get diluted out since they are being reintroduced back into the space with each air change.

The fix? Make sure the intake of your ventilation system is positioned in an area that is pulling clean air into the space and ensure the exhaust air is vented far away from the intake. Keep the intake and exhaust well-separated to avoid creating this vicious cycle.

3. Inadequate Ventilation Flow Rates

CFM, or Cubic Feet per Minute, is ventilation’s way of saying “How much air am I actually moving here?” If you don’t have enough CFM, you’re not pushing out the bad air fast enough, and the space could stay hazardous longer than you’d like, or possibly, not control the hazard at all.

Before you set up, do the math. Figure out how much air you need to move based on the size of the space and the level of contaminants you’re dealing with. Too little CFM, and you’re not doing much good. There are multiple methods to calculate the CFM required for your space (I know, math…) however, there are online calculators that can assist with this if math isn’t your strong suit. The typical formula starts with determining the volume of the confined space in cubic feet and the deciding the number of air changes per hour (ACH) required by your organization. 

"While OSHA and ANSI don't recommend a specific number of air changes per hour, a general rule of thumb is around 7 ACH before beginning work. The American Conference of Governmental Industrial Hygienists (ACGIH) recommends 20 ACH when ventilating confined spaces". 

To calculate the CFM requirements, multiple the confined space volume by the air changes per hour and divide that number by 60.

Example:

CFM =  Volume of space (ft³) X Air Changes Per Hour / 60 minutes

CFM =  2500 ft³ X 20 ACH / 60 min

CFM =  50,000 / 60 min

CFM = 833 ft³/min

After you’ve figured out your minimum CFM requirements, you can determine your minimum purge time prior to entry. You can choose to manually calculate this, use an online calculator, or use a ventilation purge time chart like the one provided here. This chart is calibrated to provide a pre-entry purge time representative of 7 complete air changes.

If you're into doing math, the formula below can be used to calculate your pre-entry purge time.

Example: 

Purge Time = Volume of Space X Pre-Entry Air Changes / CFM

Purge Time =  2500 ft³  X 7 Air Changes / 833 ft³/min

Purge Time =  17,500 / 833 ft³/min

Purge Time = 21 minutes

Ever try to suck a thick milkshake through a crazy straw? That’s what too many bends in your ventilation ducts can do to your airflow. Every bend creates resistance, slowing down the air and reducing the overall effective CFM of your ventilation system.

To avoid this, keep your ducting as straight as possible. If you do need to make a turn, go for gradual curves instead of sharp bends. This keeps the air moving smoothly and ensures that you’re getting the ventilation you need where it’s needed most. As with any piece of equipment, check the manufacturer’s guidelines for specific information. While every manufacturer will have their own guidelines for their products, most manufacturers rate their products as a decrease of around 15% per 90-degree bend with a max of two 90-degree bends. Typically this information will be provided on the device itself as seen in the picture below.

Conclusion

Ventilating a confined space is more than just a box to check—it’s about creating a safe atmosphere to work and breath in, or at least controlling the hazards to a level that’s as low as reasonably practicable. By avoiding these common pitfalls, you’re not just moving air; you’re ensuring that it’s doing its job effectively. So next time you’re setting up ventilation, remember: keep the air flowing where it needs to go, and don’t let short circuits, recirculation, inadequate CFM, or ductwork disasters stand in your way. Proper ventilation is a breath of fresh air – literally…..

ONLINE REFERENCES:

ACGIH: Ventilation

OSHA 1910.146: Permit-Required Confined Spaces

ANSI Z117.1 - 2022: Safety Requirements for Entering Confined Spaces

Chris McGlynn, M.S., CSP is a Certified Safety Professional and Nationally Registered Paramedic who serves as the Director of Safety and VPP Coordinator for Roco Rescue. He currently serves as Director-at-Large on the VPPPA Region VI Board of Directors and Secretary of the American Society of Safety Professionals Region IV Board of Directors. Chris also represents ASSP on the ANSI Z117 Confined Space and Z390 Hydrogen Sulfide Training Standard Development Committees. He is also an active OSHA Special Government Employee within the Voluntary Protection Program and is currently working towards a Ph.D in Occupational Safety & Health through West Virginia University's Statler College of Engineering. 

Are you struggling to navigate the complexities of confined space classifications? If so, you may find our latest white paper useful. This detailed analysis offers clear, practical guidance on determining whether a confined space requires a permit or can be managed under alternate entry or reclassification procedures, simplifying compliance for anyone managing a permit-required confined space program.

This guide will improve your understanding of how to properly apply the (c)(5) and (c)(7) procedures, ensuring the highest safety standards at your site. You’ll gain insights into avoiding common pitfalls, such as the prohibited practice of combining C5 and C7, which can prevent costly mistakes and ensure adherence to OSHA regulations. The paper also includes a C5/C7 Quick Reference Guide, designed to provide quick answers and streamline your decision-making process.

This paper explains the terms and requirements of C5 and C7 with straightforward language and real-world examples. It provides actionable steps to help you classify and manage confined spaces safely and efficiently. Equip yourself with the knowledge to make informed decisions about confined space safety.

Interested in a workshop or consultation from Roco Rescue? Contact us at 800-647-7626 or info@rocorescue.com.

Enhance your confined space safety program with expert insights and practical solutions.

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Perhaps the most commonly confused topic in confined space entry that I hear out in the wild is the difference between the terms entry and bodily enter. And it makes sense because, at face value, these two things sound incredibly similar. However, when we dig a little deeper and put into context, we’ll find out that they have two entirely different meanings and applications. So, let’s dive in!

To set the stage, let’s do a quick overview of the three characteristics that define a confined space. OSHA says that a confined space is a space that:

• Has limited means of access and egress, and
• Is not designed for continuous human occupancy, and
• Is large enough to bodily enter and perform work.

Remember that the space must contain all three characteristics for it to be considered a confined space. Notice the 3rd bullet point – large enough to bodily enter and perform work. We must be able to physically fit our body into the space and perform the assigned task. Now, the use of the term bodily enter stops with the definition.

Next, let’s look at what defines an entry. OSHA says an entry has occurred when any part of the entrant’s body breaks the plane of an opening into a confined space. Notice that making entry into a confined space does not necessarily mean entering with the whole body. In fact, only reaching your arm into the opening of the confined space constitutes an entry.

"So, here’s the difference. The ability to bodily enter is one of the three characteristics that define a confined space, whereas the term entry is the action of breaking the plane with any part of the body – not necessarily the whole body."

At this point, you may be thinking this is nothing more than semantics; however, this is an incredibly important differentiation.

When we understand that making entry into a confined space does not have to involve entering with our entire body, we may realize that workers in our area may have been making a lot more confined space entries than we realized. I’ve heard on numerous occasions and even seen it firsthand, where a worker sticks their arm in to turn valves or pokes their head in for a quick peek at something without going through the permit-required confined space entry procedure. After all, it’ll only take a second!

The reason this is important, and why it’s more than just semantics, is that even though a worker may be only just sticking their arm or head into a space, they could still be exposed to the hazards inside of that space. In some cases, that could have some serious consequences! For example, there may be exposed and activated rotating equipment inside of the space; so, sticking your arm or hand in may result in you being less handy around the worksite than you used to be! Alternatively, atmospheric hazards don’t just magically stop becoming hazardous right at the plane of the opening. The immediate area around the opening of the space could likely contain hazardous atmospheres as well. Sticking your head in for a quick look could be a fatal mistake.

"The time you save isn’t worth your life."

Understanding the difference between the two terms is critical for ensuring the safety of workers in and around confined spaces. The difference between the two carries significant weight, not only in definition but also in practical application. Knowing that crossing the opening of a confined space, even with just a limb, constitutes an entry and potential exposure to serious safety and health hazards is a basic fundamental concept that all workers should be well informed. So, the next time you think – I’ll just reach in and turn that valve or take a quick look – slow down and think! The time you save isn’t worth your life.

ONLINE REFERENCES:

OSHA 1910.146 PRCS

Chris McGlynn, M.S., CSP is a Certified Safety Professional and Nationally Registered Paramedic who serves as the Director of Safety and VPP Coordinator for Roco Rescue. He currently serves as Director-at-Large on the VPPPA Region VI Board of Directors and is past President of the American Society of Safety Professionals Greater Baton Rouge Chapter. Chris also represents ASSP on the ANSI Z117 Confined Space and Z390 Hydrogen Sulfide Training Standard Development Committees. He is also an active OSHA Special Government Employee within the Voluntary Protection Program.

In confined space work, ensuring air quality is a top priority. With directives from OSHA and consensus recommendations from ANSI & NFPA, understanding the ins and outs of atmospheric monitoring is key. This article will briefly review what OSHA requires as well as what ANSI, NFPA and Roco recommend for practices that ensure worker safety remains the top priority in working in these challenging environments. While the OSHA General Industry standard allows for periodic monitoring and sets no exact timespan between testing – however, as a safer way, Roco recommends continuous air monitoring any time workers are in the space.

OSHA 1910.146 refers to testing the internal atmosphere before an employee enters the space and testing as necessary to maintain acceptable entry conditions. Testing should be based on the hazard assessment for a given space as well as how rapidly those hazards could cause a change in the atmosphere, which may require additional action for safe entry.

OSHA’s Confined Spaces in Construction (1926-Subpart AA) also references monitoring frequency. It states continuous monitoring is required unless periodic monitoring is sufficient to ensure entry conditions are maintained, or continuous monitoring is not commercially available.

Note: Also take into consideration any previous work activities that may have introduced atmospheric hazards into the space as well as any known history of hazardous atmospheric conditions.

"Roco strongly encourages continuous monitoring while workers are inside a permit-required confined space."

Looking at best practice consensus standards, ANSI Z117 advocates for continuous monitoring in situations when a worker is present in a space where atmospheric conditions have the potential to change.

The national consensus standard, NFPA 350 Guide for Safe Confined Space Entry and Work 2022, also generally refers to “continuous air monitoring” when possible. Here’s a quote from NFPA 350, Section 7.13.1 (www.nfpa.org), Continuous Atmospheric Monitoring, “Atmospheric conditions can change quickly or gradually over time; without continuous atmospheric monitoring, air contaminants may increase, or the oxygen percentage may decrease or increase, creating dangerous confined space atmospheric conditions.” NFPA adds, “Entrants, Attendants, and other personnel may be unaware of changing conditions if the air quality was only initially monitored and determined to be acceptable. The atmosphere within and outside the confined space should be monitored continuously to ensure continued safe working conditions.”

PRE-ENTRY TESTING

Although OSHA does not define a specific timeline to conduct pre-entry monitoring, Roco uses as a guideline that a “baseline test” is to be conducted approximately 30 minutes prior to the entry and then again immediately prior to entry. If ventilation is being used as a control measure for atmospheric hazards, initial atmospheric monitoring should be conducted without ventilation to establish a baseline atmosphere.

A comparison of these readings could indicate that atmospheric changes have occurred inside the space. If a space has been vacated for a period of time, it is recommended that similar baseline testing be repeated. This is critical as it may reveal the presence of previously unrecognized or unanticipated atmospheric hazards.

Again, confined space work is inherently hazardous – and atmospheric hazards are a leading cause of fatalities. Do everything you can to keep your people safe. Don’t let your guard down even for a minute!

Additional Resources: 

Frequently Asked Questions: OSHA PRCS Standard Clarification 

How much periodic testing is required?

The frequency of testing depends on the nature of the permit space and the results of the initial testing performed under paragraph (c)(5)(ii)(c). The requirement in paragraph (c)(5)(ii)(F) for periodic testing as necessary to ensure the space is maintained within the limits of the acceptable entry conditions is critical. OSHA believes that all permit space atmospheres are dynamic due to variables such as temperature, pressure, physical characteristics of the material posing the atmospheric hazard, variable efficiency of ventilation equipment and air delivery system, etc. The employer will have to determine and document on an individual permit space basis what the frequency of testing will be and under what conditions the verification testing will be done.
 
What does testing or monitoring "as necessary" mean as required by 1910.146(d)(5)(ii) to decide if the acceptable entry conditions are being maintained?

The standard does not have specific frequency rates because of the performance-oriented nature of the standard and the unique hazards of each permit space. However, there will always be, to some degree, testing or monitoring during entry operations which is reflective of the atmospheric hazard.

Some of the factors that affect frequency are:

* Results of test allowing entry.
* The regularity of entry (daily, weekly, or monthly).
* The uniformity of the permit space (the extent to which the configuration, use, and contents vary).
* The documented history of previous monitoring activities.
* Knowledge of the hazards which affect the permit space as well as the historical experience gained from monitoring results of previous entries.

Knowledge and recorded data gained from successive entries (such as ventilation required to maintain acceptable entry conditions) may be used to document changes in the frequency of monitoring.

Learn More

QUESTION: How often should respiratory protection equipment be inspected, cleaned, and replaced in an industrial rescue setting?

ANSWER: 

That's a great question! While OSHA’s 1910.134 – Respiratory Protection Standard doesn't provide a specific schedule for inspection, cleaning, and replacement, it does emphasize the need for you and your company to create one. This schedule should follow the manufacturer's guidelines for your specific respiratory protection equipment. Remember that this is a general guide and not specific to your equipment.

"Always refer to the manufacturer's guidelines for the best results."

Half-face respirators are a type of protective gear that covers the nose and mouth. They use replaceable filters or cartridges to remove contaminants from the air. These respirators are ideal for environments with moderate levels of airborne hazards. Some of the places where half-face respirators are commonly used include manufacturing plants where workers are exposed to moderate levels of airborne particulates like dust, pollen, or metal fumes, as well as laboratories where there is a risk of exposure to low concentrations of hazardous chemicals or solvents during handling or mixing processes. When using half-face respirators, it is vital to inspect the facepiece for cracks, tears, or distortion. The condition of the straps or head harness should also be checked for elasticity and proper adjustment. Additionally, the inhalation and exhalation valves should be examined for any signs of damage or deterioration and inspect the filter or cartridge connections to ensure they are securely attached without any leaks.

Full-face respirators are designed to provide both respiratory and eye protection. They cover the entire face and offer superior protection against gases, vapors, and particulates. These devices are particularly useful in workplaces where workers are exposed to chemicals or toxic fumes, such as chemical processing plants or industrial painting operations. Inspection should involve checking the entire facepiece for any cracks, scratches, or damage that could compromise its integrity. The condition of the head harness and straps should also be assessed to ensure that they are intact and adjustable. Additionally, the respirator's lens should be inspected for scratches, fogging, or other impairments affecting visibility. Finally, test the operation of the inhalation and exhalation valves to ensure that they open and close correctly. 

Self-contained breathing Apparatus (SCBAs) offer the highest level of respiratory protection and are utilized in environments where the air is immediately dangerous to life or health (IDLH). They include a full-face mask connected to a compressed air cylinder worn on the back.  SCBAs are commonly used in confined spaces like storage tanks, sewers, or underground tunnels where there is a risk of oxygen deficiency or the presence of toxic gases. They are also used in firefighting operations where firefighters need respiratory protection in environments with high levels of smoke, heat, and toxic gases.

Before using SCBAs, it is important to inspect the facepiece, head harness, and straps for any signs of damage or wear. Additionally, check the cylinder for dents, corrosion, or any other signs of damage. Inspect the regulator, pressure gauge, and other components to ensure they are functioning properly. Finally, make sure that the emergency bypass valve is operating correctly.

Supplied Air Respirators (SARs) are devices that deliver clean air from an external source, such as an air compressor or compressed air cylinder, to the wearer's mask or hood. These respirators are commonly used in environments with limited oxygen or high concentrations of contaminants. SARs can be particularly useful in welding operations where workers require a continuous supply of clean air to protect against metal fumes and welding gases. 

To ensure that SARs function correctly, it is crucial to inspect the airline hose for cuts, kinks, or abrasions. Additionally, it is vital to check the connections between the respirator and the air supply source for leaks. Furthermore, ensuring that the regulator and pressure gauge are functioning correctly is crucial. Finally, verifying that the air supply source provides clean, breathable air is essential to the safe and effective use of SARs.

"It all comes down to this… The human body takes about 20,000 breaths per day. How much do you trust your equipment with one of those breaths?"

Brannon Aaron, ASP, NRP is an Associate Safety Professional through the Board of Certified Safety Professionals and a Nationally Registered Paramedic who works as a Safety Specialist and CSRT Crew Chief at Roco Rescue. Brannon has an extensive military background as well as years of experience in Pre-hospital Emergency Medical Services and emergency response settings. 

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Additional Resources

• Q&A: Cleaning Your Rescue Rope?
• Rescue Equipment Inspection Guidelines & Checklist