During transport corrosive substances pose health hazard, physical hazard or combination of both. Primary safety concern is of course health hazard however, leakage of corrosive substances may materially damage the cargo transport unit or the vessel itself and when in contact with other cargo they may cause dangerous reactions resulting in explosion and fire.
What are corrosive substances?
Any solid or liquid which will cause severe damage when in contact with living tissue or will materially damage or destroy other goods or means of transport are corrosive substances of Class 8.
Properties of corrosive substances
There are varying properties for different corrosive substances which may cause severe health or physical hazard.
If a substance poses severe personal damage then IMDG Code in column 17 of dangerous goods list will state “causes (severe) burns to skin, eyes and mucous membranes”.
If IMDG Code states “corrosive to most metals” it means that any metal likely to be present in a ship, or in its cargo, may be attacked by the substance or its vapour. “Corrosive to aluminium, zinc, and tin” implies that iron or steel is not damaged in contact with the substance. Some of these substances can corrode glass, earthenware and other siliceous materials. Many corrosives substances only become corrosive after having reacted with water, or with moisture in the air.
How are the health hazards determined for corrosive substances?
Corrosive substances are divided into three packing groups according to their degree of hazard.
- Packing group I: Very dangerous substances and preparations;
- Packing group II: Substances and preparations presenting medium danger;
- Packing group III: Substances and preparations presenting minor danger.
For named substances the variations in danger levels through packing groups assigned in dangerous goods list of IMDG Code are based on the destructive properties on living tissue through experience, inhalation risk and reactivity with water.
For new substances and mixtures assignment of packing group must be based on length of time of contact required to cause full thickness destruction of human skin.
Below table summarizes this criterion
Assignment of packing group on basis of above table must take account of human experience in instances of accidental exposure and in absence of human experience assignment of packing group must be as per data obtained by experiments in accordance with below standards
- OECD Guideline for the testing of chemicals No. 404, Acute Dermal Irritation/Corrosion, 2002.
- OECD Guideline for the testing of chemicals No. 435, In Vitro Membrane Barrier Test Method for Skin Corrosion, 2006.
- OECD Guideline for the testing of chemicals No. 430, In Vitro Skin Corrosion: Transcutaneous Electrical Resistance Test (TER), 2004.
- OECD Guideline for the testing of chemicals No. 431, In Vitro Skin Corrosion: Human Skin Model Test, 2004.
A substance which is determined not to be corrosive in accordance with OECD Test Guideline 430 or 431 may be considered not to be corrosive to skin for the purposes of IMDG Code without further testing.
How are the physical hazards determined for corrosive substances?
Any substance which is judged not to cause full thickness destruction of intact skin tissue but which exhibit a corrosion rate on either steel or aluminium surfaces exceeding 6.25 mm a year at a test temperature of 55°C when tested on both materials is considered as corrosive and be assigned to packing group III. Method of testing is prescribed in the Manual of Tests and Criteria, part III, section 37.
Emergency Response on board ships for incidents involving Corrosive Substances
Corrosive substances are extremely dangerous to humans, and many may cause destruction of safety equipment. Burning cargo of class 8 will produce highly corrosive vapours. Consequently, wearing self-contained breathing apparatus is essential. Corrosive solids and liquids can permanently damage human tissue. Some substances may corrode steel and destroy other materials (e.g. personal protection equipment). Corrosive vapours are highly toxic, often lethal by destroying lung tissue. All corrosive chemicals will be dangerous to human health (toxic). Avoid direct contact with the skin, protect against inhalation of vapours or mists.
The use of self-contained breathing apparatus and appropriate chemical protection (e.g. chemical suit) is recommended in all cases. Washing spillages and forcing vapours overboard with water-spray is the method in all cases. It is important to shut off, close and secure all ventilation leading into the accommodation of choice, machinery spaces and the bridge. All personnel should stay away from effluent (see SPILLAGE SCHEDULE S-B in Emergency Response Procedures for Ships Carrying Dangerous Goods (EmS Guide) published in the supplement of IMDG Code).
Some corrosive substances are also flammable. In these cases, the safety advice for both flammable and corrosive substances should be followed. Use of copious quantities of water and water-spray is recommended. In general, the flammability hazard is more important than the corrosive properties for the safety of the ship and the crew (see e.g. SPILLAGE SCHEDULES S-C and S-G in Emergency Response Procedures for Ships Carrying Dangerous Goods (EmS Guide) published in the supplement of IMDG Code).