CTM 9.2 A1	Chemical Tanker Manual CTM Hazards of Chemical Cargoes - Description	Doc No.: CTM 9.2 A1 Revision: 01 Date: 15 Oct 2024 Issued by: DPA Approved by: MD

1. CARGO FLAMMABILITY

• Vapour given off by a flammable liquid will burn when ignited provided it is mixed with certain proportions of air.
• If the vapour mixture is too lean or too rich it will not burn. The range in which it will burn is called the flammable range.
• For the purposes of the safe handling procedures dealt with in this guide, the flammability characteristics of cargoes are divided into three broad categories according to the flash point:
• Flammable cargoes - those with a flash point below 60°C
• Combustible cargoes - those with a flash point above 60°C
• Non-Combustible cargoes - those which have no flash point and do not burn

2. CHEMICAL HAZARDS

2.1 Chemical reactivity (CDI 5.5.3, CDI 5.5.4)

• Chemicals may react in numerous ways such as with itself, with water, with air, with other chemicals or with other materials.
• Chemical reaction may produce heat which in turn may:
• Accelerate the reaction,
• Cause the release of a large volume of vapour and/or pressure rise, or
• Cause the formation of flammable and/or harmful vapours that otherwise would not be expected.
• In principle, the dangers arising from chemical reaction are those of increased fire and health hazards.

Five main types of reaction must be considered:

2.1.1 Self-Reaction

• The tendency of a chemical to react with itself, air or contact with certain metals may promote reaction.
• Polymerisation is a common type of chain reaction or self-reaction (E.g.: Styrene monomer).
• Heat produced by the process accelerates it.

2.1.2 Reaction with air:

• Certain cargoes especially ethers and aldehydes react with oxygen to form oxygen compounds (peroxides) which if allowed to build-up may cause an explosion.

2.1.3 Reaction as a result of mixing with water:

• Certain cargoes react with water in a way that could pose a danger to ship and its personnel.
• Toxic gases may be evolved. Examples are Sulphuric Acid and isocyanates.
• Some cargoes react with water in a slow process that poses no safety hazards, but can cause damage to equipment or tank material.

2.1.4 Reaction with other cargoes:

• Some cargoes react dangerously with one another.

2.1.5 Reaction with other materials:

• Some materials may react with the product and trigger a self-reaction within the product.
• Some alloys will react in a non-hazardous way, but render the product unusable or in case of an edible product, inedible.

2.2 Corrosiveness

• Acids, Anhydrides and Alkalis are commonly carried corrosive substances.
• Corrosive liquids generally corrode normal construction materials at an excessive rate and require compatible materials for the cargo tanks and equipment to ensure their safe containment.
• When corrosion takes place, there is a release of hydrogen gas, which is highly flammable. Contact with fibrous materials such as cloth, sawdust, etc. may in some cases cause ignition of the material.
• Some corrosive liquids are also combustible.
• Human health is affected through the corrosive nature of the cargo.

2.3 Toxicity

• Toxicity may be described as the ability of a substance to cause damage to living tissue, impairment of the central nervous system, severe illness or, in extreme cases, death.
• The health hazard is a result of exposure of personnel to contact with the cargo liquid or vapour. Cargoes may be harmful when:
• In contact with the skin,
• Vapours are inhaled,
• Liquid is swallowed.
• The seriousness of the effect depends on both the physical properties of the cargo and on its toxicity.
• Absorption of a cargo through the skin depends on the solvent nature of cargo.
• Some cargoes pass readily through the skin, while in many cargoes no skin absorption takes place, even though the liquid is a poison.
• The inhalation hazard of a cargo depends primarily on its volatility.
• A cargo, which is not volatile at normal handling temperatures, may not produce sufficient vapour to be dangerous, even if the cargo is inherently poisonous.

Toxic concentrations

The two most common methods of expressing the concentration of a toxic material in the atmosphere are TWA and MAC as explained below:

• Threshold Limit Value (TLV) also called PEL (Permissible exposure Limit). An air borne concentration of a product expressed in ppm by volume in air. These values represent conditions under which it is believed that nearly all workers may be repeatedly exposed, day after day, without adverse effects. The values refer to time-weighted average (TWA) concentrations for a notional working day.
• TWA (Time-Weighted Average) (TWA) concentrations believed to be safe for the average person during an 8-hour work day and 40-hour work week for prolonged periods. The susceptibility of individuals will vary.
• Maximum Acceptable Concentrations (MAC) These values are defined as the limits that should never be exceeded. For gases and vapours, both are expressed in parts per million (ppm). Fumes, mist, and dust are similarly valued.

2.4 Anaesthesia

• Certain vapours have an anaesthetic effect and may cause loss of consciousness due to its effect on the nervous system. Anaesthetic vapours could be both toxic or non-toxic.

2.5 Putrefaction

• Most animal and vegetable oils undergo decomposition over time, this natural process is called putrefaction (going off) that:
• Generates obnoxious and toxic vapours and
• Depletes the oxygen in the tank.
• All vapours produced by cargoes liable to putrefaction may not be due to it, some may not be obvious.
• Carbon Monoxide (CO) (TLV: 25 ppm), which is colourless and odourless can be produced when an animal/vegetable oil is overheated.
• There have been numerous fatalities when crew have entered tanks for sweeping/squeeging without checking the tank atmosphere properly.