Examples of such spaces are
Oxygen shortage in these spaces affects the brain faster than any other part of the body and since oxygen content of the atmosphere falls below 21% in such enclosed spaces, breathing become faster and with more effort. When oxygen supply is below 16% the brain is quickly affected and at 10% unconsciousness is unavoidable and the individual will die if not revived and removed to fresh atmosphere. At oxygen levels below 5% unconsciousness is immediate with irreversible brain damage.
Ventilation has to be carried out before entry is permitted into an enclosed space. This may be either Forced ventilation, where at least two air changes are done before entry is made or Natural ventilation where the space is allowed to breath for at least 24 hours.
In double bottom tanks, ventilation is ensured by filling the compartment with clean seawater and then pumping it out. Regardless of the ventilation method employed, entry must be made only after the tests have shown that the atmosphere inside is breathable - contains 21% oxygen and no noxious hydrocarbon or other toxic gases
Gas tests are done to ensure safety. Oxygen is depleted by oxidization and tanks containing amounts of rusty colored water are highly dangerous. The first test should be to ensure the atmosphere throughout the space contains 21% of oxygen by volume since even 19% oxygen may be breathable but it is not considered "Safe". Entries at such low levels are made only to save life with full backup.
The second test should be to ensure that no hydrocarbon gases are present and zero readings on explosimeters are shown. Carbon Monoxide, inert gas (Tankers), exhaust fumes (Car Carriers) and Methane (formed by rotting vegetable/animal products in dirty bilge/ballast water) may be present. Before entry is permitted, the Master or a Senior Responsible Officer must ensure that tests have been made by a competent individual.
Procedure of Entry: Entry into an enclosed space should be made only with the Master's or Senior Responsible Officer's signed consent on an approved form or "Check List".
Check list should contain the following
1. Spaces to be entered and reasons for entry
2. Entry and exit points.
3. Results of atmosphere checks and details of ventilation method.
4. Names of persons entering, times of entry and duration.
5. Method and frequency of communication.
6. Name of the linkman.
7. At least one compressed air breathing apparatus set must be positioned at the point of entry, with revival unit and rescue equipment consisting of life-lines and harnesses.
8. The coordinator is on duty to sound the emergency alarm without delay if a problem occurs.
9. Personal oxygen meters are issued - if available
The Master is personally responsible for the safety of every man entering an enclosed space and he must ensure that a "Responsible Officer" is in charge of the operation and that the check lists are complied with. He must ensure communications are happening between the individuals inside and the officer outside and that an emergency support officer is on watch in the engine room, where alarms can be raised to send in the emergency team.
Rescue operations can be