Case Study: In 2004, a construction worker was found unconscious at the bottom of a newly constructed sewer pipe for a housing development. He had been working alone, grouting cracks after a vacuum test found that the pipe had atmospheric leaks. The medical examiner requested an air sample of the manhole, and it was found to have low oxygen levels. After a second test, the area was found to have unusually high levels of carbon dioxide, a common part of the air we breathe. In this case, the carbon dioxide was present in dangerously high amounts. This is common in areas with a lot of limestone, since acid leached from the soil produces carbon dioxide when it contacts limestone, and this then displaces the oxygen in the area, especially after a vacuum test. Carbon dioxide is colorless and odorless, so the worker could not have known the area was dangerous without using specialized equipment. In this case, the employer had not obtained a permit for this confined space, which would have required an atmosphere test.
Key Takeaways: Not all hazards are immediately obvious. This is why testing and monitoring are extremely important for your safety, as is having someone monitoring a confined space while the entrant works. The person in this case was luckily rescued, but these regulations are in place so that no one has to rely on luck to save their lives.
