Under the Health and Safety at Work (Hazardous Substances) regulations you may be required to obtain written permission from your neighbours if the separation distance required for the storage of your hazardous substances extends over your property boundary.
WorkSafe have just released a position document outlining when you need an agreement, and when WorkSafe recommend that you do.
In short, if your hazardous substances
then you will need a written agreement for the distance to extend across the boundary. The actual separation distance to the item must still be achieved.
If the neighbouring property does not have any of the items being separated from, then a written agreement is still recommended. For example if you are looking at the separation of a flammable liquids store from protected places, and the property that that distance goes into does not have any protected places on it at all (e.g. it is an empty section, or a public roadway).
Overall it is always best to try to ensure all the separation distances for your hazardous substances remain within your boundary where possible.
Call Chemsafety’s hazardous substances compliance team if you have any questions regarding separation distances at your site. If you are in this situation your compliance certifier will be asking about these agreements.