In which correct place should we check gas detector before start Confined Space Entry Job? Thank You Very Much and Best Regards.

inside confined space there are three places top middle and bottom we check gas detector. for example we are working in oil tank first we take top side reading after middle and then bottom if main hole is in top side.

When doing work and using the gas detector, one must remember that you are testing for gas or oxygen levels. The gas detector should be lowered to the point of work by means of a rope, to determine the conditions that the people will work in. This information must be recorded on the permit to work.