Toxicity

Exposure to toxic or poisonous substances causes harm to human health and in more extreme cases can lead to serious injury or death.
Toxicity is an intrinsic property of a chemical and cannot be modified. Even the slightest exposure to a highly toxic substance can result in serious health problems.
However, correct medical first aid treatment following exposure can mitigate the consequences.

Exposure to Toxicity

There are three ways where toxic poisons can enter the body:

A chemical may be toxic by more than one of these routes. For example, toxic vapours and mists affect people mostly via the respiratory system, but they can also be absorbed through the skin.
A highly toxic substance is one where only a small quantity of the substance is needed before harm is caused.
During chemical carrier operations, contact with a liquid or inhalation of its vapour is the most likely forms of exposure. Safe operating procedures, a full understanding of the dangers involved and the use of the correct Personal Protective Equipment (PPE) will all help to protect the crew from exposure to toxic products.

Toxicity can be defined as acute, sub-acute or chronic:

A substance with acute toxicity is sufficient to cause harm almost immediately after exposure. Substances commonly called poisons have extreme acute toxicity;
A substance with sub-acute toxicity will only start to show symptoms after repeated exposure in doses too small to cause an immediate acute effect; or
A substance has chronic toxicity if its effects only appear after repeated exposure over a period of time. Examples are substances which are carcinogenic (cancer inducing) such as benzene.

Most common exposure limits:

TLV – TWA (Time Weighted Average) The concentration of vapour in air which may be experienced for an eight hour day or 40 hour week throughout a person’s working life. This is the most commonly quoted TLV.

TLV – STEL (Short Term Exposure Limit) The maximum concentration of vapour in air allowable for a period of up to 15 minutes, provided that there are not more than four exposures per day and at least one hour between each. The STEL is always greater than the TWA however this figure is not always provided for all substances.

TLV – C (Ceiling) The absolute maximum concentration of a vapour to which a person should be exposed which should never be exceeded. It is given only for fast-acting substances. This is the highest of the three values for a given substance.

Safe containment is the first objective when handling any toxic substance. By ensuring that the chemical and its vapour are safely contained within the boundaries of the approved cargo system, and by the use of closed monitoring and control systems, the crew will be protected effectively.

Chemical carriers are designed to provide for the safe and secure handling and storage of toxic cargoes. However, accidents and failure of equipment can occur and therefore it is essential that the ship’s containment systems are well maintained and tested on a regular basis in order to ensure that they workasdesigned.

Some operations inevitably involve opening the system and potentially exposing the crew to toxic substances. Disconnecting cargo hoses at the manifold or while taking cargo samples are typical examples of where exposure can occur. During such operations, it is essential that crew members are properly protected by appropriate PPE.