Hey you didn't mentioned which safety course diploma you are talking about. There are quite a number of courses like Industrial Safety, Hospital safety etc.

I am recommending you books about Industrial Safety:

1. Fundamental of Industrial Safety by KU Mistry
2. Industrial Safety Management by LM Deshmukh
3. Industrial Safety and Environment by Amit Gupta

I hope my answer helps you. All the very best for your future endeavors!