This chapter highlights the fact that preparatory work is more important than the work itself. Many times people get killed inside tanks and other confined spaces because of misunderstandings like entering without permission to do some job or merely put their head inside to inspect the inside. Sometimes entry was authorized, but not all of the hazardous material had been removed or it had leaked back in because the isolation was poor. Sometimes hazardous material was deliberately introduced to carry out tests. Sometimes people have entered a confined space to rescue someone who has collapsed inside and been overcome. Therefore, to have a safe confined space, tanks should be built or a hole dug in the ground, it is a thumb rule to treat them in confined spaces when the depth is greater than the diameter. The chapter also discusses incomplete isolation, hazardous materials introduced, weaknesses in protective equipment, and the poor analysis of atmosphere