A turnaround puts more people inside vessels, towers, drums, and tanks in a few weeks than the plant sees in the rest of the year. Every one of those entries depends on the same question: is the air inside safe to breathe, and will it stay that way while the crew is working?
Air monitoring is how you answer that question. This article covers why it matters most during a turnaround, what the rules require, and where programs tend to fall short.
Why the air is the main hazard
You cannot see, and often cannot smell, the conditions that kill people in confined spaces. Its reported that of 1,030 confined space fatalities between 2011 and 2018, more than 60 percent were tied to hazardous atmospheres. Many of those deaths include would-be rescuers who went in after a coworker without knowing what was in the air.
What makes a turnaround different
During normal operation, a vessel is closed, and its contents are known. During a turnaround, the same vessel is opened, cleaned, purged, and worked on, and each of those steps can change the atmosphere:
- Purging. Nitrogen and steam push out hydrocarbons, but they also push out oxygen. A vessel can read clean for flammables and still not support life.
- Residue. Sludge, scale, and deposits release hydrocarbons, hydrogen sulfide, or benzene when they are disturbed or warmed by the sun.
- The work itself. Welding, cutting, coatings and solvents consume oxygen or add contaminants after the entry has started.
- Neighbors. Engines, compressors and adjacent jobs can send carbon monoxide or vapors into an open manway.
- Volume of work. Dozens of entries run at once, across shifts and contractors, which makes it easy for a re-test to be missed after a break.
The point is that a space that tested clean at 7 a.m. is not guaranteed to be clean at 10 a.m.
What OSHA requires
The permit-required confined space standard, OSHA 29 CFR 1910.146, requires the atmosphere to be tested before entry and monitored as needed to confirm that acceptable conditions are maintained. Testing is done in a set order, because each reading depends on the one before it:
- Oxygen: Acceptable range is 19.5 to 23.5 percent.
- Flammable gases and vapors: Below 10 percent of the lower explosive limit.
- Toxic gases and vapors: Below the permissible exposure limit for each substance that could be present.
Gases also settle in layers. Hydrogen sulfide and many hydrocarbon vapors are heavier than air and collect at the bottom; lighter gases rise. OSHA guidance calls for testing roughly four feet ahead of the entrant in the direction of travel and to each side, and for moving slowly enough that the instrument and its sample hose have time to respond.
Pre-entry testing is the start, not the finish.
The general industry rule allows periodic monitoring and does not set a fixed interval. That flexibility is where many programs get into trouble. We recommend any time workers are inside a permit space, and consensus standards such as ANSI Z117 and NFPA 350 point the same way. A recent Occupational Health & Safety article makes the same case: confined space atmospheres are not static, so a single pre-entry reading can create a false sense of security.
For turnaround work, where conditions change with every step of the job, continuous monitoring should be the default and periodic testing the exception you have to justify.
What good air monitoring looks like on a turnaround
- Match the sensors to the hazard. A four-gas monitor (oxygen, LEL, hydrogen sulfide, carbon monoxide) is the baseline. Add a photoionization detector or specific sensors where benzene, ammonia, or other toxics are possible.
- Bump test and calibrate. Check every instrument against a known gas before the shift, and keep the records with the permit.
- Test all levels. Sample top, middle, and bottom before entry, and allow for the length of the sample hose.
- Re-test after every break. Lunch, shift change, a stop for weather, or any change in the work is a reason to test again.
- Set clear action levels. Everyone on the permit should know which reading means stop work and leave the space.
- Plan the rescue before the entry. Monitoring tells you when to get out. A trained standby rescue team is what gets someone out who cannot leave on their own.
Specialist contractors can help with the equipment and manpower. Firms such as Code Red Safety supply gas monitors, attendants, and remote confined space monitoring for turnarounds, and Roco Rescue provides confined space rescue teams and training. Remote systems are also changing how the work is done: in one refinery case study published by Industrial Scientific, area monitors linked to Code Red software sent live gas readings from towers more than 200 feet tall, which removed manual readings and shortened permit delays.
How Moore Engineered Solutions can help
Equipment only works inside a program that tells people what to test, how often, and what to do with the result. Our Health and Safety team reviews confined space and air monitoring programs before a turnaround, checks them against OSHA requirements, and helps write site-specific procedures your crews and contractors can follow.
If you have a turnaround coming up and want a second look at your confined space entry plan, contact us.