The Health and Safety at Work (Hazardous Substances) Regulations 2017 require some hazardous substances to be separated from protected and public places by separation distances based on the hazard classification of the substance, the quantity on site and the nature of the site.

Calculating separation distances

Our calculation tool can assist PCBUs to calculate the separation distances that apply to the hazardous substances they may use, manufacture or store.

The separation distance determinations are based on the quantities and hazard classifications of the substances, and some further parameters which the user will enter in the tool.

If a hazardous substance has multiple hazard classifications (for example, 6.1B and 8.2B) the separation distances may need to be assessed individually for each of these classifications. Unless specifically mentioned otherwise, the largest separation distance will need to be adopted to ensure adequate protection.

Calculation tool

The calculation tool is a guide only. It is intended to assist PCBUs to calculate separation distances in relation to a set quantity of hazardous substances of a certain classification. 

Separation distances calculation tool (ZIP 196 KB)

To use the tool:

  • Download the zip file using the link above.
  • Locate the file on your computer.
  • Double click on the file. The file should 'unzip' and you will see the separation distances spreadsheet.
  • Open the spreadsheet and save to your computer. 
  • Click 'Enable content' in the spreadsheet (macros are needed for the spreadsheet to work). 
  • Notes:
    • For ease of use, when selecting values in the drop-down menus confirm with ‘Enter’ to improve the response times of the calculation tool.
    • You can also provide site details in the highlighted fields and are able to collapse the explanatory text at the beginning to have a concise printable summary for your own records.

Measuring separation distances

Separation distances are measured so that:

  • Any separation distance, unless the context otherwise requires, is the shortest horizontal distance between the relevant points. This means that PCBUs are generally unable to measure separation distances along certain walls, the distance is measured directly through them. There exist a few exceptions, which compliance certifiers may be able to assist with.
  • A separation distance must not, unless the context otherwise requires, extend beyond the boundary of the property at which the relevant hazardous substance is present. However, the owner, lessee, sub-lessee, occupier, or person in possession of any property beyond that boundary may agree in writing that the separation distance may include the adjacent property. Our position on hazardous substances located near property boundaries provides further information.

Reduced separation distances

In certain circumstances, separation distances may be reduced. A compliance certifier should be contacted for further information on this.

Also see the application of reduced separation distance for Class 6 and 8 substances

What is a controlled zone?

Some of the distances referred to in the calculation tool are controlled zone distances instead of separation distances.

A controlled zone is an area abutting a hazardous substance location which provides members of the public who are located outside the zone with reasonable protection from adverse effects. The PCBU will also need to ensure that, within the controlled zone, any adverse effects of hazardous substances are reduced or prevented. This may include having no incompatible substances or ignition sources present in the zone.


Explosive substances (class 1) technically do not have a separation distance or controlled zone requirement. For explosive articles a blast overpressure requirement is applicable instead.

This means that the PCBU will need to ensure that explosives are stored at a sufficient distance away that any potential adverse effect will not lead to a shockwave or blast overpressure of a specified strength for the respective environment surrounding the explosives storage.

Further information and a separate tool to determine these blast overpressure distances can be found here: Explosives (including pyrotechnics)