Back to Nautical	Draft, Trim & Stability	Securing Cargo	Deck Cargo	Container Cargo	Bulk Cargo
	Grain Cargo	Cargo Care	IMDG	Cargo Handling Equipment	Cargo Handling Safety
	Oil Tanker	Cargo Measurement	Enclosed Spaces

Cargo Work

Enclosed Space Entry

An enclosed space is one with restricted access that is not subject to continuous ventilation and in which the atmosphere may be hazardous due to the presence of hydrocarbon gas, toxic gases, inert gas or oxygen deficiency. This definition includes cargo tanks, ballast tanks, fuel tanks, water tanks, lubricating oil tanks, slop and waste oil tanks, sewage tanks, cofferdams, duct keels, void spaces and trunkings, pipelines or fittings connected to any of these. It also includes inert gas scrubbers and water seals and any other item of machinery or equipment that is not routinely ventilated and entered, such as boilers and main engine crankcases.

Many of the fatalities in enclosed spaces on oil tankers have resulted from entering the space without proper supervision or adherence to agreed procedures. In almost every case the fatality 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 deaths have occurred from impulsive and ill-prepared rescue attempts.

Respiratory hazards from a number of sources could be present in an enclosed space. These could include one or more of the following:

Respiratory contaminants associated with organic vapours including those from aromatic hydrocarbons, benzene, toluene, etc.; gases such as hydrogen sulphide; residues from inert gas and particulates such as those from asbestos, welding operations and paint mists.

Oxygen deficiency caused by, for example, oxidation (rusting) of bare steel surfaces, the presence of inert gas or microbial activity.

Hydrocarbon Vapours

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 which 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.

Oxygen Deficiency

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.

Other Atmospheric Hazards

These include toxic contaminants such as benzene or hydrogen sulphide, which could remain in the space as residues from previous cargoes.

ATMOSPHERE TESTS PRIOR TO ENTRY

General

Any decision to enter an enclosed space should only be taken after the atmosphere within the space has been comprehensively tested from outside the space with test equipment that has recently been calibrated and checked for correct operation.

It is essential that all atmosphere testing equipment used is:

Suitable for the test required;

Of an approved type;

Correctly maintained;

Frequently checked against standard samples.

A record should be kept of all maintenance work and calibration tests carried out and of the period of their validity. Testing should only be carried out by personnel who have been trained in the use of the equipment and who are competent to interpret the results correctly.

Care should be taken to obtain a representative cross-section of the compartment by sampling at several 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 10 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. Hence, when descending to the lower part of a tank or compartment, further atmosphere tests should be made. Regeneration of hydrocarbon gas should always be considered possible, even after loose scale has been removed. The use of personal detectors capable of continuously monitoring the oxygen content of the atmosphere, the presence of hydrocarbon vapour and, if appropriate, toxic vapour is strongly recommended. These instruments will detect any deterioration in the quality of the atmosphere and can provide an audible alarm to warn of the change in conditions.

While personnel remain in a tank or compartment, ventilation should be continuous and frequent atmosphere tests should be undertaken. In particular, tests should always be made before each daily commencement of work or 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.

Hydrocarbon Vapours

To be considered safe for entry, whether for inspection, cold work or hot work, a reading of not more than 1% LFL must be obtained on suitable monitoring equipment.

Benzene

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 Permissible Exposure Limits (PEL’s) are likely to be exceeded. Tests for benzene vapours can only be undertaken using appropriate detector equipment, such as that utilizing detector tubes.

Detector equipment should be provided on board all vessels likely to carry cargoes in which benzene may be present.

Hydrogen Sulphide

Although a tank which has contained sour crude or sour products will contain hydrogen sulphide, general practice and experience indicates that, if the tank is thoroughly washed, the hydrogen sulphide should be eliminated. However, the atmosphere should be checked for hydrogen sulphide content prior to entry and entry should be prohibited in the event of any hydrogen sulphide being detected. Hydrogen sulphide may also be encountered in pumprooms and appropriate precautions should therefore be taken.

Oxygen Deficiency

Before initial entry is allowed into any enclosed space, which is not in daily use, the atmosphere should be tested with an oxygen analyzer to check that the normal oxygen level in air of 21% by volume is present. This is of particular importance when considering entry into any space, tank or compartment that has previously been inerted.

Generally nearly all substances have been assigned Permissible Exposure Limits (PEL) and /or Threshold Limit Values (TLVs). The term Threshold Limit Value (TLV) is often expressed as a time weighted Average (TWA). The use of the term Permissible Exposure Limit refers to the maximum exposure to a toxic substance that is allowed by an appropriate regulatory body.

The PEL is usually expressed as a Time Weighted Average, normally averaged over an eight-hour period.

Short Term Exposure Limit (STEL), is normally expressed as a maximum airborne concentration averaged over a 15-minute period.

The values are expressed as parts per million (PPM) by volume of gas in air. Toxicity can be greatly influenced by the presence of some minor components such as aromatic hydrocarbons (e.g. benzene) and hydrogen sulphide. A TLV of 300PPM, corresponding to about 2%LEL, is established for gasoline vapours.

Entry Procedures

General

An entry permit should be issued by a responsible officer prior to personnel entering an

enclosed space. An example of an Enclosed Space Entry Permit is provided in ISGOTT.

Suitable notices should be prominently displayed to inform personnel of the precautions to be taken when entering tanks or other enclosed spaces and of any restrictions placed upon the work permitted therein.

The entry permit should be rendered invalid if ventilation of the space stops or if any of the conditions noted in the checklist change.

No one should enter any cargo tank, cofferdam, double bottom or other enclosed space unless an entry permit has been issued by a responsible officer who has ascertained immediately before entry that the atmosphere within the space is in all respects safe for entry. Before issuing an entry permit, the responsible officer should ensure that:

The appropriate atmosphere checks have been carried out, namely oxygen content is 21% by volume, hydrocarbon vapour concentration is not more than 1% LFL and no toxic or other contaminants are present.

Effective ventilation will be maintained continuously while the enclosed space is occupied.

Lifelines and harnesses are ready for immediate use at the entrance to the space.

Approved positive pressure breathing apparatus and resuscitation equipment are ready for use at the entrance to the space.

Where possible, a separate means of access is available for use as an alternative means of escape in an emergency.

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 a responsible officer. The lines of communications for dealing with emergencies should be clearly established and understood by all concerned.

In the event of an emergency, under no circumstances should the attending crew member enter the tank before help has arrived and the situation has been evaluated to ensure the safety of those entering the tank to undertake rescue operations.

Regular atmosphere checks should be carried out all the time personnel are within the space and a full range of tests should be undertaken prior to re-entry into the tank after any break.

The use of personal detectors and carriage of emergency escape breathing apparatus are recommended.

Reference should be made to ISGOTT for additional guidance on entry into pumprooms.