When should the first tests for explosive gases in a manhole be conducted?

The first tests for explosive gases in a manhole should be conducted before removing the manhole cover. This is crucial for ensuring safety, as there could be hazardous gases present that may pose a risk of explosion or harmful exposure. Conducting these tests prior to the cover removal allows workers to assess the potential risk and take necessary precautions to protect themselves and the environment.

By testing before accessing the manhole, personnel can determine the presence of flammable or toxic gases like methane or hydrogen sulfide. If such gases are detected, appropriate safety measures can be implemented, such as ventilation or the use of protective equipment, before any further actions are taken.

It's critical to prioritize safety in confined spaces like manholes, which can often harbor dangerous conditions due to limited airflow. Therefore, conducting tests beforehand is a standard safety practice in collections system maintenance.