Final answer:
The precaution recommended before entering a confined space with the presence of hydrogen sulfide is to not enter until there is no hydrogen sulfide detected and all safety equipment is in place. Therefore, correct option is d.
Step-by-step explanation:
The precaution recommended before entering a confined space with the presence of hydrogen sulfide is option d) Do not enter the confined space until there is no hydrogen sulfide detected, and then only when all safety equipment is in place.
Hydrogen sulfide is a toxic gas that can be harmful if inhaled. It is necessary to exercise caution and take appropriate safety measures before entering a confined space where hydrogen sulfide is present.
Wearing a gas mask at all times (option a) and entering immediately with safety equipment (option b) are not sufficient precautions, as the concentration of hydrogen sulfide can still pose a risk. It is important to ensure that the confined space is free from hydrogen sulfide and to have all the necessary safety equipment in place before entering.