Many people have been killed inside tanks and other confined spaces.
Sometimes they have entered without permission to do so or merely put
their head inside an open manway 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 isolation was poor. Sometimes hazardous
material was deliberately introduced in order to carry out tests. Sometimes
people have entered a confined space to rescue someone who has
collapsed inside and been overcome themselves