A Hazardous Chemical is any substance in such a form or quantity that would pose an unreasonable risk to health, safety or the environment should it be released from its container.
A Hazardous Chemical Incident is the release or potential release of a hazardous chemical from its container into the environment.
Factors which influence the level of risk with hazardous chemical incidents include:
The toxicity of a chemical can be referred to in a number of different ways:
Lethal Dose, 50% Kill (LD-50) is the concentration of a chemical that would result in death for 50% of people if ingested or injected;
Lethal Concentration, 50% Kill (LC-50) is the concentration of a chemical that would result in death for 50% of people if inhaled;
Threshold Limit Value/Time Weighted Average (TLV/TWA) is the maximum airborne concentration of a chemical to which an average healthy person can be exposed repeatedly for eight hours each day for 40 hours per week without suffering adverse effects;
Threshold Limit Value/Short Term Exposure Limit (TLV/STEL) is the maximum concentration to which a person should be exposed for up to 15 minutes at a time, for a maximum of four times per day with a minimum of 60 minutes between each time;
Threshold Limit Value/Ceiling (TLV/C) is the maximum concentration to which a person should be exposed even for an instant;
Permissible Exposure Limit (PEL) is also known as the Recommended Exposure Limit (REL), and is the maximum average concentration that will cause no adverse effects to 95% of healthy adults continually exposed during a 40 hour working week.
Exposure to Chemicals
Exposure to chemicals can occur by:
1. Inhalation ie by being breathed; 2. Absorption ie through the skin; 3. Ingestion ie by being swallowed; 4. Injection ie from a needle, nail or splinter.
The dose of a chemical that a person receives is dependant on the concentration of the chemical and the length of time that the person is exposed. The larger the dose, the larger the effect.
Acute poisoning is the result of a single exposure to a high concentration of a toxic chemical, and the symptoms appear soon after exposure.
Chronic poisoning is the result of repeated exposure to a relatively low concentration of a toxic chemical, and the symptoms develop over a longer period of time.
Acute poisoning to the skin will cause blistering, whereas chronic poisoning will cause dryness and cracking.
Certain chemicals will not have an effect on the point of contact, but once in the bloodstream can effect other parts of the body. This is known as a remote effect, as opposed to a local effect.
Responding to a Hazardous Chemical Incident
When the director of a response to a Hazardous Chemical Incident arrives on the scene, the situation must be carefully appraised and a decision made on whether the personnel on site can handle the incident with the equipment that is available. If not, the situation should be contained until emergency services arrive.
Accurate information is needed on the chemicals involved, and possible effects from contact with other chemicals in the vicinity, so that the risks involved can be fully evaluated.
Due to the large number of hazardous chemicals manufactured, information will not always be available for the combination of chemicals involved in a particular incident, and the knowledge of on-site personnel familiar with the chemicals should be used.
Identification of Hazardous Chemicals
To assist in assessing the risk posed by chemicals, they are categorised into classes and divisions:
Class Division 1. Explosives 2. Compressed Gases Flammable Poisonous (Toxic) Non Flammable 3. Flammable Liquids Highly Flammable (F.P. below 23oC) Flammable (F.P. 23oC - 61oC) 4. Flammable Substances Flammable Solids Spontaneously Combustible Water Reactive 5. Oxidising Substances Agents Organic Peroxides 6. Poisonous Substances Toxic Infectious 7. Radioactive Substances 8. Corrosive Substances 9. Miscellaneous Dangerous Substances
All hazardous chemicals should carry a label to indicate which class they belong to, and the particular hazard involved. Class Labels, as in the example below, are diamond shaped with the class (and division) name and number in the bottom half and a symbol showing the hazard in the top half.
There are standard class labels for classes one to eight, plus a striped label used on vehicles to indicate that a mixed load is carried. The size of a label is dependant on the risk involved, the larger the label, the greater the risk.
Dealing with a Hazardous Chemical Incident
Mine sites should have readily available information on the properties and behaviour of all hazardous chemicals on site and communications arrangements with technical personnel for advice to rescuers in the event of a hazardous chemical incident.
To assist personnel responding to a hazardous chemical incident make decisions on the action to be taken, vehicles and storage areas containing bulk quantities of hazardous chemicals should have clearly visible Emergency Information Panels, as per the following example:
The name at the top left part of the panel is the correct technical name of the substance. Where more than one hazardous chemical is carried or stored, this space is left blank.
The UN No. is a four digit number recognised by the United Nations that identifies each chemical. The Fire Brigade has a computerised data-base of information on hazardous chemicals based on their United Nations numbers.
The hazchem code provides information on how a spill or a fire involving the particular chemical should be treated, plus the minimum level of personal protection required. The hazchem code is interpreted using a Hazchem Card:
The digit that starts the code indicates which agent should be used for fighting a fire and/or dispersing a spill of the chemical. Should the recommended agent not be available, it is safe to use a higher number, but not a lower number. For example, if foam is prescribed, it is safe to use a dry agent but not fog (water spray).
Where a spill involving a hazardous chemical requires the use of breathing apparatus, and it is certain that fumes of a low concentration from only one chemical will be encountered, a chemical filter mask can be used. Mines Rescuers must familiarise themselves with the type of chemical filter masks on their mine site, and must know the duration of usage for which the filter will give guaranteed protection. Before using a chemical filter mask, always check that the filter is definitely the correct type for the hazard and mask, check the 'use-by' date and that the caps are in place. Once the mask has been donned, the facemask seal should be checked by placing the palm of the hand over the inlet of the filter and inhaling.
Where the hazchem code indicates that full body protective clothing is to be worn, hooded PVC overalls rated as suitable for the chemical risk should be worn over work clothes with the cuffs of the legs fastened over rubber boots, the cuffs of the sleeves fastened over PVC gloves (with the open end of the glove folded over) and the hood secured over the facemask seal. Waterproof tape should be used on the cuffs, hood and zip to guarantee a complete seal., A tab should be created with the tape around the facemask so that it can be easily removed. Also, a decontamination site should be set up just inside the cordoned off area at the entry point.
The decontamination site should be clearly delineated and is made up of a cleaning area downwind and downhill from an undressing area. If the hazchem code indicates that containment is required, the cleaning area should be made into a water tight dam. If the code prescribes dry agent, a vacuum cleaner may be required and the decontamination site should be in a sheltered area. If dry agent is not specified, a soft broom and a decontamination shower or a water hose will be needed.
After assisting the entry party dress and don their sets, the back-up party will dress themselves in the same manner. When the entry party is seen to be returning, the back-up party will attach the demand valves to their facemasks and enter the undressing area.
Any casualties brought back by the entry party should be stripped and thoroughly cleaned by the entry party before being handed to the back-up party to be passed on to medical aid.
The back-up party will move to the cleaning area and decontaminate the party member with the lowest cylinder pressure first. This may involve using a neutralising agent then scrubbing the rescuer while they are washed.
The procedure followed is:
If the PVC overalls are not certain to be totally impervious to the chemicals involved in the incident, they should be disposed of, otherwise they and the BAs should be re-cleaned before being stored. While in storage, the PVC overalls should regularly be checked for signs of degradation or damage.
The operation is complete when all areas back to the entry point have been cleaned, after having been neutralised if appropriate. If a dam was used for the cleaning area, its contents should be placed in a container for disposal.
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