Use of Acutely Very Toxic Substances


The description "Very Toxic" is defined by CHIP as:

Acute lethal effects:

  • R28 "Very Toxic if swallowed": LD50 oral, rat < or = 25mg/kg : less than 100% survival at 5mg/kg oral, rat.
  • R27 "Very Toxic in contact with skin": LD50 dermal, rat or rabbit: < or = 50mg/kg.
  • R26 "Very Toxic by inhalation"; LC50 inhalation, rat, for aerosols or particulates < or = 0.25mg/litre/4hr.
  • LC50 inhalation, rat, for gases and vapours < or = 0.5mg/litre/4hr.

Non-lethal irreversible effects after a single exposure:

  • R39 "Danger of very serious irreversible effects": Irreversible damage is likely to be caused by a single exposure by an appropriate route, generally in the above dose ranges. In order to indicate the route of exposure, combinations of Risk Phrases may be used e.g. R39/23 i.e. " Danger of very serious irreversible effects by inhalation".


High risk of death from a single dose. For a robust individual of 80kg, ingestion of less than 0.5g of an R28 substance can be fatal. It should be noted that this is the upper limit - some substances may be more toxic than this. Also lesser doses whilst not being fatal may still be severely damaging.



Prevention of Exposure

As usual for hazardous materials, the first route of protection is to avoid exposure totally by using a safer alternative. If such an alternative is available and its use is "reasonably practicable" then this must be done. However, toxic and other properties of possible chemical substitutes should be established and taken into account when considering changes. Synthetic routes should be chosen to avoid the use of very toxic starting materials and to avoid, as far as possible, the formation of by-products, intermediates, wastes or residual contaminants consisting of or containing very toxic substances.

However, if there is no practicable alternative to using a very toxic substance then a COSHH Special Assessment must be completed for that substance in written form.

Control of Exposure

If use of a safer alternative substance is not reasonably practicable, then adequate control of exposure must be ensured.

In addition to the principles of Good Laboratory Practice laid down in the COSHH Standard Assessment, the following rules must also be applied or more strongly emphasised:

  • All users of very toxic substances must be fully aware of the hazards associated with using the substance and of the route(s) by which the particular substance(s) can enter the body, be it by inhalation, ingestion or by penetration of the skin, mucosal surfaces or eyes. This will require a thorough reading of Safety Data Sheets and other sources of information.
  • The preferred method of controlling exposure is by total containment of the substance or process. This is unlikely to be possible in a research environment but must be employed if reasonably practicable. 
    The number of people likely to be exposed to the very toxic substances and the duration of their exposure must be kept to a minimum.
  • Only the minimum amount of the very toxic substances necessary may be used. This applies also to stored material which should be kept to a minimum.
  • Very toxic materials must be stored in closed containers that are clearly labelled and marked with visible hazard and warning signs. Preferably, all such substance containers should be stored in locked, ventilated cupboards fitted with trays to contain spillage and clearly marked with warning and hazard signs.
  • Very toxic materials that are normally stored in glass containers may be transported only within robust, secondary containers large enough and capable of containing any spills arising from breakage.
  • Very toxic material may be used only within a fume-hood of good quality and effectiveness.
  • The appropriate protective clothing must be worn including gloves of material that provide real protection against accidental skin contact.
  • Great care must be taken to avoid spreading contamination from the site of use. This will involve the following precautions:
    • Material may be weighed only within an adequate fume-hood or other well ventilated enclosure,
    • Care must be taken to avoid contaminating the exterior of containers. Any such contamination must be cleaned off within the fume-hood before returning to store and the cleaning material disposed of as chemical waste,
    • Care must be taken to avoid the formation of airborne dust or processes that may give rise to aerosols,
    • Apparatus must be cleaned within the fume-hood and any washings, including solvent, carefully stored as waste. Alternatively, any very toxic residues may be chemically destroyed- if so, the procedure for destruction must be written down as part of the COSHH Assessment,
    • Spill etc. within the fume-hood must be cleared up carefully and any materials used disposed of as chemical waste,
    • Gloves must be disposed of as chemical waste. Users must never touch door handles, light switches or telephones with (assumed contaminated) gloves or wear such gloves outside of the laboratory. Gloves should be removed using the proper "surgical" procedure to avoid skin contamination,
    • Users must practice careful hygiene and wash and dry hands thoroughly before leaving the laboratory.
  • The use of "sharps" in procedures should be avoided because of the additional danger of self- injection.
  • Disposable "sharps", including broken glass must be decontaminated before disposal and the washings treated as chemical waste.
  • Waste material must be securely stored and clearly labelled prior to disposal. Very toxic materials must never be disposed off by the waste solvent route
  • Procedures using these materials must never be attempted by an untrained person.
  • Procedures using these materials must never be attempted out of normal working hours or over the lunch period when trained First Aiders may not be available.
  • Procedures using these materials must never be attempted by someone working alone and for larger scale operations, workers should operate in pairs.

Level of Risk Remaining

Constant vigilance is required in the use of these materials but risks should be low if the procedures outlined above are followed.


Emergency Procedures

  • Skin Contact. Immediately wash with soap and water and remove contaminated clothing. Call a First Aider
  • Eye Contact. Wash with copious amounts of water. Call PSSO (ext 2691).
  • Ingestion. Obtain urgent medical attention. Call PSSO (ext 2691).
  • Inhalation. Obtain urgent medical attention. Call PSSO (ext 2691).
  • Failure of Services: Work should be carefully closed down, gloves removed and left, the fume-hood sashes closed and the laboratory evacuated until services are resumed

Back to Completed Risk Assessment Forms

Adapted with permission from School of Chemistry, University of Bristol