Some bulk cargoes may deplete the oxygen content of holds or produce toxic gases, what are some precautions to be taken before entry of holds?

Oxygen depletion caused by factors such as self-heating of the cargo, oxidation of metal and ores or decomposition of vegetable oils, animal fats, grain and other organic material or their residues. 1. ventilation 2. the crew is aware of dangers and has sufficient protective equipment (SCBA) to enter spaces