By Maklub Al Mostofa
For the purpose of this Guide, an ‘Enclosed Space’ is defined as a space that has the following characteristics:
- Limited openings for entry and exit.
- Unfavourable natural ventilation.
- Not designed for continuous worker occupancy
Enclosed spaces include, but are not limited to:
- Cargo spaces
- Double bottoms
- Fuel tanks
- Ballast tanks
- Cargo pump-rooms
- Cargo compressor rooms
- Chain lockers
- Void spaces
- Duct keels
- Inter-barrier spaces
- Engine crankcases
- Engine scavenge air receivers
- Sewage tanks
Many of the casualties that have occurred in enclosed spaces on ships have resulted from people entering an enclosed space without proper supervision or adherence to agreed procedures. In almost every case, the casualty would have been avoided if the simple guidance in this Chapter had been followed.
The rapid rescue of personnel who have collapsed in an enclosed space presents particular risk. It is a human reaction to go to the aid of a colleague in difficulties, but far too many additional and unnecessary casualties have occurred from impulsive and ill-prepared rescue attempts.
Assessment of Risk
In order to ensure safety, a risk assessment should be carried out. Gas tests carried out prior to entry into the space should reflect the contaminants that can reasonably be expected to be present within the space, taking into account the previous cargo carried, ventilation of the space, structure of the tank, coatings in the space and any other relevant factors.
When preparing for entry into a ballast tank or void space where hydrocarbon vapours may not normally be present, it is prudent to test the space for hydrocarbon vapour or H2S if the space is adjacent to a cargo or bunker tank. This is particularly important if entry is being made to investigate the possibility of bulkhead defects.
Respiratory hazards from a number of sources could be present in an enclosed space. These could include one or more of the following:
- Hydrocarbon vapours, such as butane and propane.
- Toxic contaminants associated with organic vapours, such as aromatic hydrocarbons, benzene, toluene etc.
- Toxic gases, such as benzene, hydrogen sulphide and mercaptans.
- Oxygen deficiency caused by the presence of inert gas, oxidation (rusting) of bare steel surfaces, or by microbial activity.
- Solid residues from inert gas and particulates, such as those from asbestos, welding operations and paint mists.
During the carriage and after the discharge of hydrocarbons, the presence of hydrocarbon vapour should always be suspected in enclosed spaces for the following reasons:
- Cargo may have leaked into compartments, including pumprooms, cofferdams, permanent ballast tanks and tanks adjacent to those that have carried cargo.
- Cargo residues may remain on the internal surfaces of tanks, even after cleaning and ventilation.
- Sludge and scale in a tank that has been declared gas free may give off further hydrocarbon vapour if disturbed or subjected to a rise in temperature.
- Residues may remain in cargo or ballast pipelines and pumps.
The presence of gas should also be suspected in empty tanks or compartments if non-volatile cargoes have been loaded into non-gas free tanks or if there is a common ventilation system which could allow the free passage of vapours from one tank to another.
Toxic contaminants could be present in the space as residues from previous cargoes, such as benzene or hydrogen sulphide. To be considered safe for entry, whether for inspection, Cold Work or Hot Work, a reading of less than 1% LFL must be obtained on suitable monitoring equipment.
Checks for benzene vapour should be made prior to entering any compartment in which a cargo that may have contained benzene has recently been carried. Entry should not be permitted without appropriate personal protective equipment, if statutory or recommended TLV-TWAs are likely to be exceeded (see Section 18.104.22.168). Tests for benzene vapours can only be undertaken using appropriate detector equipment, such as detector tubes. Detector equipment should be provided on board all ships likely to carry cargoes in which benzene may be present.
- Hydrogen Sulphide
H2S is present in some crude oils and in some products in varying concentrations. Where the concentration is high, the oil is often referred to as being ‘sour’. H2S is very soluble in water. General practice and experience indicates that washing a tank with water after carrying a cargo containing H2S should eliminate the hydrogen sulphide vapour within the space.
However, prior to entry into an enclosed space which has previously carried oil containing H2S, or where the presence of H2S vapour may be expected, the space should be ventilated to a reading of less than 1% LFL on a combustible gas indicator and tested for the presence of H2S using a gas detector tube. Care should be taken not to rely on the use of catalytic H2S sensors which may have a cross-sensitivity with hydrocarbon vapour. Since H2S is heavier than air, it is very important that the bottom of any space is thoroughly tested.
When carrying a cargo containing H2S, particular attention should be given to the possibility of the presence of H2S in locations such as pumprooms, deck stores and in ballast tanks. There is a high probability of the presence of H2S in ballast tanks due to the gas being drawn into the tank when deballasting during the loading operation.
Mercaptans are present in the vapours of pentane plus cargoes and in some crude oils. They may also be present where oil residues have been in contact with water for extended periods. The presence of Mercaptans can be detected by the use of chemical detector tubes. Their concentration should be reduced to 0.5 ppm to avoid discomfort to personnel and nuisance smells.
Before initial entry is allowed into any enclosed space, the atmosphere should be tested with an oxygen analyser to check that the air contains 21% oxygen. This is of particular importance when considering entry into any space, tank or compartment that has been previously inerted. Lack of oxygen should always be suspected in all enclosed spaces, particularly if they have contained water, have been subjected to damp or humid conditions, have contained inert gas or are adjacent to, or connected with, other inerted tanks.
Products of Inert Gas
By-products of combustion when inert gas is produced from boiler flue gas or from an inert gas generator include carbon monoxide and carbon dioxide.
Carbon monoxide is a toxic gas that may be present in cargo tank atmospheres following gas freeing and in spaces containing components of the inert gas plant. Carbon dioxide is not toxic, but presents a smothering hazard. Adequate ventilation is required to maintain a normal oxygen level in air of 21% by volume in the space and to eliminate any hazard.
Atmosphere Tests Prior to Entry
No decision to enter an enclosed space should be taken until the atmosphere within the space has been comprehensively tested from outside the space with test equipment that is of an approved type and that has recently been calibrated and checked for correct operation.
The appropriate atmosphere checks are:
- Oxygen content is 21% by volume.
- Hydrocarbon vapour concentration is less than 1% LFL.
- No toxic or other contaminants are present.
Care should be taken to obtain measurements from a representative cross-section of the compartment by sampling at various depths and through as many deck openings as practicable. When tests are being carried out from deck level, ventilation should be stopped and a minimum period of about ten minutes should be allowed to elapse before readings are taken.
Even when tests have shown a tank or compartment to be safe for entry, pockets of gas should always be suspected.
If extensive work is to be carried out within a large space, such as a cargo tank, it is recommended that a full assessment of the tank atmosphere is undertaken after the initial tests have been satisfactorily carried out and recorded. The person undertaking the full assessment should enter the tank carrying an emergency escape breathing device and a personal gas monitor, in addition to the gas testing instrument. The tank atmosphere should be checked frequently during this entry, with particular attention being placed on testing the work location(s) and places that are inaccessible for testing from the deck. On satisfactory completion of this additional atmosphere test, the results should be recorded as required by the appropriate safety procedure in the Safety Management System.
While personnel are in a tank or compartment, ventilation should be continuous. Regeneration of hydrocarbon gas should always be considered possible, even after loose scale or sludge has been removed. Continual checks on the atmosphere in the space should be made as specified in the Safety Management System.
Atmosphere tests should always be made after any interruption or break in the work. Sufficient samples should be drawn to ensure that the resulting readings are representative of the condition of the entire space.
When entering cargo and bunker tanks, all the tanks and spaces adjacent to the space to be entered should also be tested for hydrocarbon gas and oxygen content and, where appropriate, the inert gas pressure should be lowered to reduce the possibility of any inter-tank leakage. Notwithstanding this precaution, personnel should remain alert to the possibility of leakage of hydrocarbon gas from adjacent spaces or from pipelines running through the tank.
Control of Entry into Enclosed Spaces
It is the responsibility of the Company to establish procedures for safe entry of personnel into enclosed spaces. The process of requesting, raising, issuing and documenting permits to enter into an enclosed space should be controlled by procedures in the ship’s Safety Management System (SMS). It is the Master’s responsibility to ensure that the established procedures for entry into an enclosed space are implemented.
The Master and Responsible Officer are responsible for determining whether entry into an enclosed space may be permitted. It is the duty of the Responsible Officer to ensure:
- That the space is ventilated.
- That the atmosphere in the compartment is tested and found satisfactory.
- That safeguards are in place to protect personnel from the hazards that are identified.
- That appropriate means for controlling entry are in place.
Personnel carrying out work in an enclosed space are responsible for following the procedures and for using the safety equipment specified.
Prior to entry into an enclosed space, a risk assessment should be completed to identify the potential hazards and to determine the safeguards to be adopted. The resulting safe working practice should be documented and approved by the Responsible Officer before being countersigned by the Master, who confirms that the practice is safe and in compliance with the ship’s Safety Management System. The permit, or other enabling document, should be sighted and completed by the person entering the space, prior to entry.
The controls required for safe entry vary with the task being performed and the potential hazards identified during the risk assessment. However, in most cases, an Entry Permit System will provide a convenient and effective means of ensuring and documenting that essential precautions have been taken and, where necessary, that physical safeguards have been put in place. The adoption of an Entry Permit System, which may include the use of a check-list, is therefore recommended.
Permission to continue work should only be given for a period sufficient to complete the task. Under no circumstances should the period exceed one day.
A copy of the permit should be prominently displayed at the entrance to the space to inform personnel of the precautions to be taken when entering the space and of any restrictions placed upon the activities permitted within the space.
The permit should be rendered invalid if ventilation of the space stops or if any of the conditions noted in the check-list change.
Restricting the issue of approvals, such as entry permits, so that all cargo tanks which are safe to enter are shown on one document, may be found to simplify the paper administration, avoid overlapping and reduce the possibility of confusion as to which approval applies to which tank. However, if such a system is used, there must be rigorous control to ensure cancellation of existing permits, and that the atmospheres of all named tanks are correctly tested at the time of issue so that an effective extension of a period of validity does not occur by default. It will be particularly important to ensure that the permit process is supplemented by the marking of tank lids with notices indicating which tanks are safe to enter.
Inspection of cargo tanks after cleaning and before loading can require an independent surveyor to enter the tank. All relevant tank entry procedures must be observed.
Safeguards for Enclosed Space Entry
Before allowing access to the space, the Responsible Officer should ensure that:
- Appropriate atmosphere checks have been carried out.
- Piping, inert gas and ventilation systems have been isolated.
- Effective ventilation will be maintained continuously while the enclosed space is occupied.
- Fixed lighting, such as air-turbo lights, are ready for extended entry periods.
- Approved self-contained, positive pressure breathing apparatus and resuscitation equipment is ready for use at the entrance to the space.
- A rescue harness, complete with lifeline, is ready for immediate use at the entrance to the space.
- A fully charged approved safety torch is ready for immediate use at the entrance to the space.
- A responsible member of the crew is in constant attendance outside the enclosed space, in the immediate vicinity of the entrance and in direct contact with the Responsible Officer.
- All persons involved in the operation should be trained in the actions to be taken in the event of an emergency.
- Lines of communications have been clearly established and are understood by all concerned.
- Names and times of entry will be recorded and monitored by personnel outside the space.
The personnel undertaking the task should ensure that such safeguards are put into effect prior to entering the space.
The personal protective equipment to be used by people entering the space must be prescribed. The following items should be considered:
- Protective clothing including work clothing or protective suits, safety boots, safety helmet, gloves and safety glasses.
- For large spaces, or where climbing access will be undertaken, the wearing of safety harnesses may also be appropriate.
- Approved safety torches.
- Approved UHF radio.
- Personal gas detector or an area gas detector and alarm.
- Emergency Escape Breathing Device(s).
Evacuation from Enclosed Spaces
If any of the conditions that are stated on the permit for entering the space change, or the conditions in the space are suspected of becoming unsafe after personnel have entered the space, personnel should be ordered to leave the space immediately and not be permitted to re-enter until the situation has been re-evaluated and the safe conditions stated on the permit have been restored.
Sample of Enclose Space Entry:
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