Some time ago, OSHA received notification of a construction site fatality where an employee was found at the bottom of a newly installed manhole. The employer was a small construction company that installed water and sewer lines, and was completing a project laying sewer pipe and constructing manholes for a new housing development.
There were six employees on-site the day of the incident. Five of the employees were laying pipe over the hill from the manhole where the incident occurred. The victim was grouting the manhole.
The work area was previously farmland and was slightly hilly. The manhole was placed in the terrain with a slope of 1-4, and was adjacent to entrance ramps to a highway. The manhole had four sections, with a total height of approximately 17 feet when measured on the outside (per drawings). The inside measurement was 16½ feet when measured with a trench pole. All of the sections were made of concrete and were coated with a water proofing substance. Ladder rungs were present in the interior surface.
At the time of the incident and the inspection activity, the inlets were plugged. The project manager installed a vacuum pump at the opening of the manhole and pulled a vacuum to test the tightness of the joints. Because the test failed, the joints required grouting. Workers didn’t follow confined space protocols. Everyone thought there was no hazard because the manhole was new.
Further investigation revealed the vacuum pulled in-ground gasses that suffocated the worker as he descended into the manhole. In the Midwest, acidic soil can combine with limestone (calcium carbonate) causing a neutralization reaction that produces carbon dioxide (CO2). The vacuum test pulled a higher-than-normal level of this CO2 into the manhole space, which displaced the oxygen.
The moral: Be aware that hazards exist in new construction. Confined space protocols were developed to eliminate these hazards. Make sure you understand when and where you should use these protocols.