Hazard Knowledge

Substances that cause health effects are commonly referred to as toxic, harmful or poisonous. These terms refer to a substance’s ability to cause injury or damage to a human being, an animal or the environment.

Uncontrolled materials that can affect health pose a significant hazard to responders if appropriate controls are not implemented to prevent exposure. In addition to posing risks to health, many of these materials will also present other hazards for the worker or emergency responder. This section deals only with those that relate to the acute health effects of the materials.

Two subcategories differentiate the way in which harm is caused:

• Acute health effects
• Chronic health effects

Acute health effects occur immediately or soon after contact with the hazard. They have a threshold level below which no harm can be observed, although for highly toxic substances this level can be extremely low.

Once symptoms are observable, their severity increases with increased dose, ultimately leading to the death of the organism that was exposed. This is known as the lethal dose. For inhalation hazards, this dose will depend on two key factors; the concentration in air and the time someone is exposed to this concentration.

These are the symbols fire and rescue service personnel are likely to see in relation to acute health hazards and acute toxicity:

Chronic, or long-term, health effects occur as a result of repeated or prolonged exposure to a hazardous material, or where the health effect arises long after the exposure occurs, such as exposure to cancer-causing agents.

The likelihood of chronic health effects increases with prolonged or repeat exposure. However, the severity of the symptoms is the same – for example, a cancer-causing substance can only lead to the development of a cancer or cancer will not develop at all. The likelihood of cancer increases with exposure.  

Fire and rescue service personnel are likely to see the following symbols in relation to chronic health hazards. The transport classification and labelling systems do not include classifications for chronic hazards. Therefore, materials that cause chronic effects can only be identified through the Classification, Labelling and Packaging (CLP) labelling. For further information on the categories of toxic materials see A foundation for hazardous materials.

Four routes of exposure can lead to symptoms developing:

• Ingestion
• Contact with skin or eyes (skin absorption)
• Inhalation
• Injection or through cuts

The route through which exposure occurs can also be a significant factor in the speed and type of symptoms displayed. For example, exposure through a cut may mean that some hazardous substances get absorbed into the blood stream more quickly, enabling symptoms to develop rapidly.

Further details can be found in National Operational Guidance: Hazardous materials Control measure - Signs and symptoms of exposure

Substances with acute toxicity need to reach a certain accumulated amount within the body before the onset of symptoms. This is referred to as the dose. Beyond this amount, further exposure will increase the total dose received, causing the severity of symptoms to increase.

The total dose received is a result of both the concentration that an individual is exposed to and the duration of exposure. For example, a short exposure to a high concentration of a substance will lead to the same symptoms as longer exposure to a lower concentration.

The exact symptoms for a given dose are specific to the substance’s toxicity but also the susceptibility of the individual exposed. Certain populations are typically more vulnerable to the health effects of hazardous materials, for example, the young and elderly.

A number of data sources provide information for levels of exposure and the expected effects. For further information, see National Operational Guidance: Hazardous materials Control measure – Substance identification, Control measure – Specialist advice: Hazardous materials and A foundation for hazardous materials.

Where a substance is known to display toxic health hazards, this information can be obtained from data sources such as safety data sheets (SDS). However, a number of substances have low intrinsic toxicity but can react to liberate toxic substances, particularly gases. The most common examples are materials that liberate combustion products with toxic effects, such as carbon monoxide.

In such cases where reactions or fire are involved, scientific advice should be sought to assist in identifying the level of hazard posed by the reaction or combustion products formed.

Asbestos

Asbestos-containing materials (ACMs) that are in good condition and left undisturbed cannot cause ill health as fibres will not be released. Handling or touching ACMs that are in good condition will also generally not present a risk. However, when they are disturbed or damaged, fibres are released into the air. Inhaling asbestos fibres is a major hazard to human health. Inhaled fibres can become lodged in the lungs and the body’s natural defences are not able to break them down. The principle diseases known to be caused by exposure to asbestos fibres are asbestosis, lung cancer, malignant mesothelioma and asbestos pleural disease.