FAQs about confined space entry

Responding is David D. Wagner, director of applications engineering and product knowledge, Industrial Scientific Corp., Pittsburgh.

Confined space entry is one of the most challenging issues faced by safety professionals today. Although much attention is paid to the ins and outs of the topic, much about confined space entry is still misunderstood. For instance, what is the difference between a “permit required” and “non-permit-required” confined space?

OSHA defines a confined space in 29 CFR 1910.146 as any space that (1) is large enough and so configured that an employee can bodily enter and perform work, (2) has limited or restricted means for entry or exit, and (3) is not designed for continuous employee occupancy. By definition, a space must meet all three criteria to be classified as a confined space. A small area that is enclosed and has a restricted entry area, but is intended to be occupied for work on a 24/7 basis, is not considered to be a confined space.

A permit-required confined space is defined by OSHA in the same standard to be any space that (1) contains or has the potential to contain a hazardous atmosphere, (2) contains a material that has the potential for engulfing an entrant, (3) has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls or by a floor that slopes downward and tapers to a smaller cross-section, or (4) contains any other recognized serious safety or health hazard. Unlike non-permit-required spaces, where all of the characteristics of the definition of a confined space must be met for an area to truly be considered a confined space, the existence of any of the criteria that define a permit-required confined space elevates the classification of the space to the permit level.

Once a space has been classified as a permit-required confined space, the atmosphere must be tested prior to entry to make sure conditions inside are safe for the entrant. Although the fact that the atmosphere must be tested from outside the space implies that a monitor must use a pump to draw a sample of the atmosphere from within the space, it raises a question: Is lowering a gas detector that records peaks down into the space acceptable if the space is dry?

Sampling the atmosphere from outside the space using a monitor with a sample pump is the preferred method of pre-entry testing and is definitely considered to be the best practice. Lowering a monitor into the space potentially subjects what should be considered a sensitive piece of electronic equipment to damage from anything that might be contained within the space, such as sludge, water or other liquids.

Even if the space is dry and has no real potential for the monitor to sustain damage, there is no way to be certain at what location within the space the peak values have been recorded.

If gases have stratified in the space at concentrations just below the detector’s alarm points, the gas tester will have no idea where within the space the hazard is located, making it more difficult to correctly assess and mitigate the hazard. With that said, when no monitor with a sample pump is available, lowering a diffusion-based monitor into the space to perform the test is better than entering the space with no testing at all.

Many of these questions and other mysteries of confined space entry can be answered by consulting NFPA 350, the NFPA’s newly released technical and best practice guide to safe entry in confined spaces.