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Handling of toxic chemicals onboard - chemical tankers safety procedure

What is a toxic substance?
A toxic substance is one which is liable to cause either harm to human health, serious injury or death. Toxic means the same as poisonous. Toxicity is an intrinsic property of a chemical, which man cannot modify, and its effect is a function of exposure. In some cases, correct response to its effects after exposure can diminish its consequences.

There are three common ways that a cargo can be toxic: swallowed (oral toxicity), absorbed through the skin, eyes and mucous membranes (dermal toxicity) or inhalation as a vapour or mist (inhalation toxicity).

A chemical may be toxic by more than one of these routes: for example, toxic vapours and mists affect people most via the respiratory system but they can also be absorbed through the skin. The smaller the quantity (or dose) of the substance that is required to harm health, the more toxic a substance is. In some cases the toxic effect of a chemical can be countered by administering antidotes, but in most cases the hazard must be avoided by correct use of protective clothing, breathing apparatus and ventilation procedures. If there is no exposure to the chemical, or if exposure is reduced to safe levels, there can be no toxic effect.

In tanker operations, contact with a liquid or inhalation of a vapour are the most likely forms of exposure. In general, proper procedures and proper use of personal protective equipment will prevent exposure and thus the effects of toxicity.

Toxic effects

Toxicity can be acute, sub-acute and chronic. A substance has acute toxicity if a single exposure is sufficient to cause harm almost immediately. Substances commonly called poisons have extreme acute toxicity.

A substance with sub-acute toxicity displays its effects after a person has had repeated exposures to doses too small to cause an acute effect. Examples are allergic sensitisers, which induce reactions to other substances.

A substance has chronic toxicity if its effects appear after a period of continuous exposure to doses too low to cause any acute effect. Examples are carcinogens (cancer inducing), teratogens and mutagens (which affect reproduction).

Threshold limit value (TLV)

A threshold limit value for a given substance is the maximum concentration of its vapour in air to which it is believed that personnel may be exposed under certain circumstances without suffering adverse effects. Various governmental bodies publish TLVs. These should not be regarded as the absolute dividing line between safe and hazardous conditions. It is good operating practice to keep all vapour concentrations to a minimum and a safe margin below the TLV.

The best known list of TLVs is issued by the American Council of Governmental Industrial Hygienists (ACGIH). The values are updated annually in the light of new knowledge, so it is important to refer to the latest edition. The ACGIH defines three categories of TLVs:

Precautionary principles

Containment is the first objective when any toxic substances are handled, by making sure that they stay inside the cargo system. Engineering and ship design features will provide a secure storage space. If there is no exposure there is no toxicity danger, however hazardous the chemical can be. Leakage of liquid or release of vapour must be prevented by keeping the cargo system closed unless it is absolutely unavoidable to open it.

However, some operations inevitably involve opening the system; for example, disconnecting a hose from the ship's manifold after transfer of cargo. Although this is a routine operation, it should be regarded as - comparable to opening up a cargo line elsewhere on deck, and operators must wear the necessary personal protective equipment.

Toxic vapour detection and personal protective equipment

Most chemical vapours are heavier than air and tend to flow along the deck and accumulate in low spots, for example below pumproom floor plates. Therefore atmosphere samples should always be taken in such low points where concentrations are likely to be highest. It is important that a full chemical suit is worn by personnel when:

  1. Inspecting pipelines and machinery for leaks;

  2. Dealing with accidental leaks and spillage;

  3. Connecting and disconnecting hoses and loading arms;

  4. Taking ullages and samples from tanks (where restricted gauging is permitted);

  5. Entering enclosed spaces such as pumprooms, cofferdams and tanks unless certified gas free;

  6. Opening up pumps and equipment (unless certified gas free).

IMO Code Requirements

The IBC Code specifies ways to limit exposure of personnel to toxic vapours while cargo is being handled, or during carriage at sea.

First, it minimises toxic vapour emissions by controlling how cargo vapours are to be vented or returned to shore, and how tank contents are to be gauged. Virtually all toxic cargoes require closed or restricted tank gauges to prevent crews being exposed to unsafe concentrations of toxic vapours. Second, it specifies ventilation of working spaces such as pumprooms, requires the ship to carry equipment to detect vapours, requires the provision of personal equipment and, to ensure that toxic vapours are diluted to safe concentrations before they can reach accommodation areas, requires that tank vent system outlets are located at a safe distance. (The safe distances specified depend on the severity of the toxic hazard.)

Third, it reduces the likelihood of accidental overflow spills by specifying that all acutely toxic products and all allergic sensitisers are to be carried in tanks equipped with a visual and audible high level alarm (HLA). Tanks certified for the most severely acute toxic products must have a further overflow control system.

Finally, it specifies that cargo piping, including pumps, and venting systems of tanks carrying toxic cargoes are to be separated from those containing other products, to prevent any leakage causing toxic contamination of non-toxic products and subsequent exposure of personnel unaware of the contamination. This is achieved on many chemical tankers by having separate pumps, pipelines and vents so that segregation is achieved by design, and on ships with common pipeline systems by the engineering principle of two physical stops, such as spectacle plates or a removable spool piece and blank flanges.

Valve gland packing is the source of many small leaks. The correct packing material for the chemical being carried should always be used, and the glands correctly tightened.

The IBC Code prohibits stowage of most toxic products adjacent to oil fuel tanks. The combustion of many otherwise non-toxic chemicals may produce toxic substances such as carbon dioxide and carbon monoxide, fumes of hydrochloric acid, hydrogen cyanide and nitrogen oxides. These may be present at some distance from the fire and may have no warning odour.

Self-contained breathing apparatus should be used when dealing with chemical fires. The main danger from fume inhalation is asphyxia. Personnel affected by fumes should be removed rapidly to a fresh atmosphere, given oxygen and then treated appropriately as shown in the MFAG.


The two fundamental guides for medical first aid on board ships, which give advice on dealing with exposure to toxic cargoes, are the International Medical Guide for Ships (IMGS) and the Medical First Aid Guide for Use in Accidents Involving Dangerous Goods (MFAG). Both are published jointly by IMO, ILO (the International Labour Organization) and WHO (the World Health Organization). The IMGS gives guidance on common illnesses and is not solely concerned with chemical accidents. The MFAG is supplementary to the IMGS and contains advice for recognising and treating chemical poisoning, within the limits of the facilities available on board.

The general rule is that if, during the handling of chemicals, any person shows symptoms that suggest poisoning, they should be treated in accordance with the MFAG and seen by a doctor as soon as practicable. Medical advice should be sought by radio, while still at sea. Assistance may also be available from another ship with a doctor on board.

Emergency Treatment According to the Route of Exposure

Note that over and above the routine blood tests, as required under the crewing procedures, any crew member exposed to toxic chemicals must have their blood tested immediately after and then again as per doctor’s advice.

How to recognise poisoning

MFAG gives directions on how to recognise the general symptoms of poisoning. Note that they may not appear for some time after exposure to the chemical. Symptoms to be alert to are unexpected headaches, nausea and vomiting, drowsiness, changes in mental behaviour, unconsciousness, convulsions, or pain. If the patient has a rapid but weak pulse, a greyish blue colour of the skin, severe breathing difficulty or remains unconscious for a prolonged period, severe poisoning must be suspected.

First aid and further care

A first aider is not just a person with goodwill, but a person with training. MFAG outlines immediate first aid, i.e. treatment for minor casualties, or to enable a victim to be moved so that further treatment can be administered.

The key priorities to remember when reacting to a casualty are:

The signs and symptoms of mild poisoning usually resolve after a few hours in the majority of incidents, particularly if the degree of exposure is small. However, if a greater amount is taken in, or the period of exposure is prolonged or the chemical is very toxic, symptoms may persist for much longer, even for some days.

The patient's condition may continue to deteriorate even when clear of the source of the vapour, and systemic affects may appear. Finally, the warning is given that death may occur despite treatment.

General advice can be found in MFAG, on the emergency treatment to be administered according to the way the chemical has entered the body, for example by skin or eye contact, ingestion or inhalation. If the chemical has affected both the skin and the eyes, the latter should get priority for attention. If the chemical has been ingested, the patient should not be made to vomit because the vomit may enter the respiratory system and add to the exposure problem.

MFAG tables

Appropriate reactions after exposure to the toxic cargoes listed in the IMO Codes are given by tables in MFAG. There are 12 group tables, but five chemicals require their own single substance tables, because they present particular combinations of toxic hazards (carbon disulphide, allyl alcohol, benzene, acrylamide and tricresyl phosphate).

Emergency Schedules

The Emergency Schedules are an appendix to the IMDG Code and provide masters with advice on the immediate action to be taken in case of accidents such as spillage or leakage of toxic substances. In brief, if it is safe to do so, spillage should be collected for subsequent disposal, but if there is any doubt, the spillage should be washed overboard with plenty of water, because the safety of the crew takes priority over pollution avoidance.

We have summarized below some of the special chemical cargoes frequently carried onboard chemical tankers

Toxicology and associated hazards

Handling benzene & methanol safety precautions

Handling carcinogens requirements for certain chemical cargoes

Handling ACRYLONITRILE safety precautions

handling ISOCYANATES safety precautions

handling Sulfuric acid safety precautions

handling Phenol safety precautions

Hazards of Phenol - safe handling of Phenol on chemical tankers.

Marine transportation of Phenol and more safety guideline

Handling benzene & methanol safety precautions

Requirements of various grade chemical cargo heating

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