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Hazards Involved in Confined Spaces on board cargo ships and countermeasures

Confined spaces on board a cargo ship :Boiler, pressure vessel, cargo, ballast, fuel oil, or lube oil tank, cargo hold, void spaces, or similar type enclosures are the most commonly found confined spaces on board a cargo vessel. These area got limited openings for entry and exit, lack of natural ventilation and not designed for continuous worker occupancy

What are the Hazards Involved in Entering and Working in Confined Spaces?

Hazardous Atmospheres

The atmosphere in a confined space may be extremely hazardous because of the lack of natural air movement, presence of hydrocarbon vapors, such as butane and propane. This characteristic of confined spaces can result in 1) oxygen-deficient atmospheres - Oxygen deficiency caused by the presence of other vapors (including IG) oxidation (rusting) of bare steel surfaces, or by microbial activity, 2) flammable atmospheres, and/or 3) toxic atmospheres.

Lack of Oxygen

An oxygen-deficient atmosphere has less than 19.5% available oxygen (O2). Any atmosphere with less than 20.8 % oxygen should not be entered! The oxygen level in a confined space can decrease because of work being done, such as welding, cutting, or brazing; or, it can be decreased by certain chemical reactions (rusting, paint drying) or through bacterial action (fermentation).

The oxygen level is also decreased if oxygen is diluted by another gas, such as carbon dioxide or nitrogen, resulting from inerting or fire suppression. Total dilution of oxygen by another gas, such as carbon dioxide, will result in unconsciousness, followed by death.Respiratory hazards due presence of Toxic gases, such as Benzene, Hydrogen sulfide and Mercaptan. Toxic contaminants associated with organic vapors, such as Aromatic hydrocarbons, Benzene, Toluene, etc.

Flammable atmospheres

Two things make an atmosphere flammable: 1) the oxygen in air, and 2) a flammable gas, vapor, or dust in the proper mixture. Different gases have different flammable ranges. If a source of ignition (e.g., a sparking or electrical tool, static electricity, sand blasting) is introduced into a space containing a flammable atmosphere, an explosion will result.

An oxygen-enriched atmosphere (above 22%) will cause flammable materials, such as clothing and hair, to burn violently when ignited. Therefore, never use pure oxygen to ventilate a confined space. Ventilate with normal air.

Confined space require good ventilation prior entry
Fig: Confined space require good ventilation prior entry

Toxic environment

Unless a certified marine Chemist or a Competent person has certified a space as Safe. assume that any substance (liquids, vapors, gases, mists, solid materials, and dusts) in a confined space can be hazardous. Toxic substances may range from fast acting poisons to long term cancer causing carcinogens. Toxic substances can come from the following:

i) The product stored in the space:

The product can be absorbed into the structure and/or tank coatings and give off toxic gases when removed or when cleaning out the residue of a stored product, toxic gases can be given off. Example: Removal of sludge or mud from a tank decomposed material can give off deadly hydrogen sulfide gas and/or methane gas.

ii) The work being performed in a confined space:

Examples of such include welding, cutting, brazing, painting, scraping, sand blasting, degreasing, etc. Toxic atmospheres are generated in various processes. For example, cleaning solvents are used in many industries for cleaning/degreasing. The vapors from these solvents are very toxic in a confined space.

iii) Areas adjacent to the confined space:

Toxicants produced by work in the area of the confined spaces can enter and accumulate in confined spaces.

It is important to understand that some gases or vapors are heavier than air and will settle to the bottom of a confined space . Also, some gases are lighter than air and will be found around the top of the confined space. Therefore, it is necessary to test all areas (top, middle, bottom) of a confined space with properly calibrated testing instruments to determine what gases are present. Atmospheres may be different in individual bays of the same tank. If testing reveals oxygen-deficiency, or the presence of toxic gases or vapors, the space must be ventilated and re-tested before entering.

Testing instruments for Oxygen and Flammability read in Percent. The Oxygen Meter should indicate 20.8 % Oxygen in the space being tested. The Flammability indicator shows the percent within a safety range of 0-10% of the Lower Explosive Limit (LEL) and, ideally, should read 0%.

Toxins are measured in parts per million (PPM) usually in a glass tube that changes color to indicate the PPM content of the space. A different type of tube must be used for each toxin suspected to be present.

Testing instruments are available in several different forms, hand powered by squeezing a rubber bulb or bellows, and battery powered giving the indication either on an analog gauge or digital readout. Testing instruments must be calibrated/checked frequently to a ssure accuracy.

Enclosed space good ventilation practice
Fig: Enclosed space good ventilation practice

Ventilation requirement for working in a confined space

Ventilation by a blower, eductor or fan may be necessary to remove harmful gases and vapors from a confined space. There are several methods for ventilating a confined space. The method and equipment chosen are dependent upon the size of the confined space openings, the gases to be diluted (e.g., are they flammable?), and the source of makeup air.

Under certain conditions where flammable gases or vapors have displaced the oxygen level, but are too rich to burn, forced air ventilation may dilute them until they are within the explosive range. Also, if inert gases (e.g. carbon dioxide, nitrogen) are used in the confined space, the space should be well ventilated and re-tested before a worker may enter.

A common method of ventilation requires a large hose, one end attached to a fan and the other lowered into a manhole or opening. For example, a manhole would have the ventilating hose run to the bottom (see diagram) to dilute or displace all harmful gases and vapors. The air intake should be placed in an area that will draw in fresh air only. Ventilation should be continuous where possible, because in many confined spaces the hazardous atmosphere will form again when the flow of air is stopped. De-ballasting a tank does not guarantee a safe atmosphere. Testing is still required.

Fig:wearing appropriate PPE prior entering enclosed space is mandatory

Standby person outside of the confined space & rescue method

A standby person should be assigned to remain on the outside of the confined space and be in constant contact (visual or speech) with the workers inside. The standby person should not have any other duties but to serve as standby and know who should be notified in case of emergency. The standby person should never leave his post even after help has arrived and is a key communication link to others onboard Over 50% of the workers who die in confined spaces are attempting to rescue other workers.

Rescuers must be trained in and follow established emergency procedures and use appropriate equipment and techniques (lifelines, respiratory protection, standby persons, etc.). Steps for safe rescue should be included in all confined space entry procedures. Rescue should be well planned and drills should be frequently conducted on emergency procedures. Unplanned rescue, such as when someone instinctively rushes in to help a downed co-worker, can easily result in a double fatality, or even multiple fatalities if there are more than one would-be rescuers.


Isolation of a confined space is a process where the space is removed from service by one or more of the following :

i) locking out electrical sources, preferably at disconnect switches remote from the equipment.

ii) blanking and bleeding, securing valves Cargo, ballast, IGS , pneumatic and hydraulic lines

iii) disconnecting mechanical linkages on shaft-driven equipment where possible, and

iv) securing mechanical moving parts within confined spaces with latches, chains, chocks, blocks, or other devices.

v) Appropriate notices, which clearly specify which space and prevailing requirements agreed upon for confined space entry, should be displayed in prominent locations such as bridge, cargo control room, engine control room, etc.

Confined space fatality
Fig: Confined space fatality

Potential hazards in a confined space

In addition to the areas discussed above, evaluation of a confined space should consider the following potential hazards:

i) High temperaure:

Extremely hot or cold temperatures can present problems for workers. For example, if the space has been steamed, it should be allowed to cool before any entry is made.

ii) Engulfment hazards:

Loose, granular material stored in holds or tanks, such as grain, sand, coal, or similar material, can engulf and suffocate a worker. The loose material can crust or bridge over and break loose under the weight of a worker.

iii) Noise disturbance:

Noise within a confined space can be amplified by the design and acoustic properties of the space. Excessive noise can not only damage hearing, but can also affect communication, such as causing a shouted warning to go unheard.

iv) Slick / wet surfaces

Slips and falls can occur on a wet surface causing injury or death to workers. Also, a wet surface will increase the likelihood for and effect of electric shock in areas where electrical circuits, equipment, and tools are used.

v) Falling objects

Workers in confined spaces should be mindful of the possibility of falling objects, particularly in space which have topside opening for entry, and where work is being done above the worker.

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