Keeping crews safe in underground utility spaces means treating every entry as a planned operation. You assess the space, isolate energy and incoming flows, test the air before and during work, post an attendant topside, and have rescue ready before anyone climbs down. Miss one, and nobody goes in.
In August 2025, sewer gas overcame three workers fixing lines in a Mobile, Alabama, manhole, and two of them died, according to the Occupational Safety and Health Administration (OSHA). OSHA found the employer had no confined space entry program, no training, and no emergency plan.
You can close all three of those gaps before the cover comes off, and that's what gets your crew back up the ladder at the end of the shift.
Why Are Underground Utility Spaces So Dangerous?
Manholes and vaults have small openings and very little natural airflow. Gas from rotting sewage or a leaking line tends to collect inside, and you usually can't see or smell it.
The U.S. Bureau of Labor Statistics counted 61 worker deaths in sewers, manholes, and storm drains between 2011 and 2018, and breathing in a harmful substance was the most common cause. That's why underground utility safety starts with the air.
Live cables and sudden water surges add more risk below ground, and traffic keeps moving just a few feet from the opening.
Assess the Space and the Job Before Entry
Every space needs a fresh look before every job. A vault that tested clean last month could hold gas today if a nearby line has started leaking.
What a Pre-Entry Check Should Cover
Have a competent person look over the site before anyone opens the hole. Good hazard detection tools, like a voltage detector and a calibrated gas monitor, make that check quicker and more reliable.
Before the cover comes off, look for:
- Smoke, steam, or strange odors coming from vent holes or cover gaps
- Water pooling around the opening or flowing in from connected pipes
- Bent ladders, broken rungs, or loose cable supports inside the hole
- Idling trucks or generators that could push exhaust into the space
- Enough room around the opening for a guardrail or barrier
Know Which Rules Apply
A telecommunications crew and a contractor doing other repairs could follow separate federal standards in the very same manhole. Have your safety lead confirm which rule covers the task before confined space entry begins.
Does Anyone Really Need to Go In?
The safest entry is the one nobody has to make. In fact, pole-mounted cameras and long-reach tools can handle a lot of inspection work from the surface.
If someone does have to go down, lock out every energy source feeding the space first. That means electric lines and pumps, and it means blocking incoming water or sewage. Run ventilation fans on top of these steps, since fans only deal with the air.
Next, call the utility operator and any other crews on site so nobody restarts equipment mid-job.
Test the Air First, Then Keep Testing
Federal permit-space rules call for testing oxygen first, then flammable gases, and then toxic gases. Lower the probe to the top, middle, and bottom of the space to find gases sitting at different levels.
Testing keeps going after entry, too. Portable gas monitors clipped near each worker's collar keep reading the air and sound an alarm when levels change. RKI gas detection equipment is one example of the multi-gas monitors crews often use for this.
Station a Dedicated Attendant at the Opening
Somebody has to stay up top for the entire job. The attendant tracks who's inside and keeps in radio or voice contact with them. They're the one who calls everyone out when an alarm goes off, or a worker starts slurring words.
Make Rescue Capability a Condition of Entry
Plan the rescue before the cover comes off. Clip each entrant into a harness and lifeline tied to a tripod and winch, so the attendant can pull them out from the surface. Your rescue service should show that it can reach the site and work in this exact space before the job starts.
Train Your Crew for the Actual Job
Training should match the spaces your crew really enters, from shallow vaults to deep sewer lines. A signed permit records your controls, and the crew still needs hands-on practice using them.
Choose worker safety gear for the hazards you found. For instance, spaces with too little oxygen call for an air-supplying respirator.
Before each entry, run a short crew briefing that covers:
- Who's entering, who's attending, and who's handling rescue
- Today's gas readings and the alarm levels that mean get out
- Which energy sources you've locked out and who holds each lock
- Hand signals and radio checks for when voices don't carry
- Where the rescue gear sits and who runs the winch
Frequently Asked Questions
What Oxygen Level Is Safe for Entry?
Federal permit-space rules treat air with less than 19.5% oxygen as oxygen deficient. Air with more than 23.5% oxygen counts as oxygen-enriched. Either reading means nobody goes in until you ventilate the space and retest.
Can the Attendant Climb In to Help?
Under the permit-space rule, the attendant stays outside until another attendant takes over. Electric utility manholes work a bit differently.
OSHA's electric utility guide lets the attendant step in briefly when there's no potential hazard. When a hazard exists, like heavy traffic, the attendant has to stay above the hole.
What Extra Testing Applies When Using a Torch?
An open flame can ignite flammable gas, so it gets its own testing schedule. Crews in electric utility enclosed spaces test for flammable gases right before lighting a torch. They retest at least once an hour for as long as the flame stays lit.
The Entry Routine That Keeps Crews Safe
Every safe entry follows the same order. You assess the space, shut off energy and incoming flows, test the air before anyone goes down, and keep testing while they work. An attendant stays at the opening, and rescue gear and trained responders are ready before the first boot hits the ladder.
None of it takes long once your crew runs it on every job, and that routine is what keeps underground utility work from ending with a 911 call.
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