• What are very toxic materials?
• How are very toxic materials hazardous to my health?
• How are very toxic materials classified under WHMIS?
• How are Toxic materials classified under GHS?
• How does the GHS system and WHMIS compare regarding classification of very toxics?

What are very toxic materials?

Very toxic materials are substances that may cause significant harm or even death to an individual if even very small amounts enter the body. These materials may enter the body in different ways (called the route of exposure). The most common route of exposure is through inhalation (breathing it into the lungs). Other routes include skin contact where some materials can easily pass through the skin and enter the body. Ingestion is another, less common, route of exposure in the workplace. Ingestion often occurs accidentally through poor hygiene practices (e.g. eating food or smoking a cigarette using contaminated hands).

There are a number of very toxic materials that may be used in workplaces. Some examples include carbon monoxide, hydrogen sulfide, chlorine and sodium cyanide. Extreme care and caution must be used if there is potential for any form of exposure to very toxic materials. The table below lists some workplace materials that meet one or more of the criteria to be considered "very toxic" as well as some potential health effects associated with that toxicity.

(Note: not a complete listing of symptoms)

To prevent the possibility of adverse health effects from exposure to very toxic materials, it is important to understand the potential hazards and how to protect yourself. This document discusses the hazards of very toxic materials and how they are identified. For more information about working with very toxic materials, see the CCOHS document How do I Work Safely with Very Toxic Materials.

How are very toxic materials hazardous to my health?

The degree of hazard associated with any toxic material is related to the concentration of the substance, the route into the body and the amount absorbed by the body (the dose). Individual susceptibility of the user also plays a role. Very toxic materials are capable of causing serious and significant health effects in an exposed individual, including death. With very toxic materials, only a very small amount is required to enter the body for it to cause these adverse health effects.

Very toxic materials cause serious health effects by damaging critical body systems. This damage is often irreversible. The health effects may occur immediately or the effects may be delayed. Health effects that occur immediately after a single exposure are called acute effects. In other cases, health effects occur at some point after the exposure. This is called a chronic effect. A chronic effect may occur hours, days, months or even years after exposure. Generally, acute effects are caused by a single, relatively high exposure. Chronic effects tend to occur over a longer period of time and involve lower exposures (e.g. exposure to a smaller amount over time). Some very toxic materials can cause both acute and chronic health effects.

It is important to remember that very toxic materials can have other hazards associated with it. For example, a very toxic material may also have properties that make it an oxidizer as well as a corrosive. Always read the Material Safety Data Sheet and labels to be sure you understand what is in the product and how to protect yourself. If you do not understand or if you are not sure, check with your supervisor.

How are very toxic materials classified under WHMIS?

Under the Workplace Hazardous Materials Information System (WHMIS), very toxic materials are part of Hazard Class D -- Poisonous and Infectious Materials. Since very toxic materials can cause acute (short-term) health effects as well as chronic (long-term) health effects, WHMIS has a division for each. It is possible for a very toxic material to cause both acute and chronic health effects.

Division 1 (D1) contains "Materials Causing Immediate and Serious Toxic Effects". It is represented by the WHMIS symbol to the right. As the title suggests, these materials can cause immediate and serious health effects if an exposure occurs. Within this division, there are two additional subdivisions that separate "Toxics" and "Very Toxics". The "Very Toxics" are D1A; the "Toxics" are D1B. In this division, the primary difference between D1A and D1B is acute toxicity (e.g. LD50, LC50). D1A substances require significantly less material to produce an immediate and serious effect. Some very toxic materials are capable of causing death from a single small dose or brief exposure.

Division 2 (D2) is for "Materials Causing Other Toxic Effects". It is represented by the WHMIS symbol to the right. These materials produce toxic effects that may not appear right away and may be delayed by hours, days, months or even years. The D2 division also has two subdivisions that separate "Toxics" and "Very Toxics". The "Very Toxics" are D2A; the "Toxics" are D2B.

Under the D2A heading of "Materials Causing Other Toxic Effects", the health effects considered for very toxic materials (D2A) include:

• severe chronic toxic effects
• reproductive toxicity (material known or suspected to cause a negative impact on reproductive functions (male or female))
• teratogenicity and embryotoxicity (material known or suspected to cause a negative impact on a developing embryo or fetus)
• carcinogenicity (material known or suspected to cause cancer)
• respiratory sensitization

Under the D2 heading of "Materials Causing Other Toxic Effects", the health effects considered for toxic materials (D2B) include:

• chronic toxic effects
• skin or eye irritation
• skin sensitization
• mutagenicity (material known or suspected to cause changes to cells)

How are Toxic materials classified under GHS?

The goal of the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) is to provide a harmonized approach to classifying chemical hazards as well as communicating health and safety information (e.g. through labels and safety data sheets). The intent is to have all countries using similar chemical classification, labelling and communication guidelines in order to reduce errors and misunderstandings.

Under the GHS system, there are three major hazard groupings -- physical, health and environmental. Toxic materials are categorized under the Health Hazards. Some of the toxic and very toxic materials will have characteristics that place them in more than one class or group (e.g., the same way that a material can have multiple WHMIS symbols).

The GHS system has set up a method for classifying very toxic materials using the following health hazard classes:

• acute toxicity (e.g. LD50, LC50)
• skin irritation/corrosion
• serious eye damage/eye irritation
• respiratory or skin sensitization
• mutagens (material known or suspected to cause changes to cells)
• carcinogens (material known or suspected to cause cancer)
• reproductive toxicity (material known or suspected to cause a negative impact on reproductive functions (male or female) or on a developing fetus)
• specific target organ toxicity -- single exposure (materials that produce an adverse effect on one or more organ systems in the body after a single exposure)
• specific target organ toxicity -- repeated exposure (materials that produce an adverse effect on one or more organ systems in the body after repeated exposure)
• aspiration hazard (a liquid or solid material that may enter the body's respiratory system directly through the nose or mouth)
• chemical mixtures

The GHS class for "acute toxicity", for example, has five categories and there are specific criteria used to determine under which category the material belongs. This criterion helps determine the degree of hazard. Pictograms and signal words (e.g. Danger, Warning) are used to convey the hazard(s) about the material. GHS will also use Safety Data Sheets (SDS) to provide information about any known hazards associated with the material.

How does the GHS system and WHMIS compare regarding classification of very toxics?

The GHS classification system is somewhat more complex than WHMIS and a classification in one system does not necessarily translate directly into the other.

While the GHS system does goes into more detail regarding the classification of very toxic materials than WHMIS does, it does not change the actual hazard associated with the material. The goal of the GHS system is to express the hazard of a particular material in a very specific and structured way.

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Document confirmed current on August 1, 2011

Document last updated on June 8, 2009

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