Anyone walking around Avonmouth this afternoon (November 3) will have heard a loud siren ringing out.
The Severnside area contains a number of sites, including the Esso terminal, which handle hazardous substances.
To keep residents safe, a siren system is maintained by the Severnside Sirens Trust.
The sirens - which can be heard across Portishead, Avonmouth, Shirehampton, Pilning and Severn Beach - warn people of possible incidents involving dangerous substances.
However, anyone concerned about today's noise might be comforted to know that it was only a test.
The sirens are tested on the third day of each month at 3pm.
If you hear the Severnside Sirens at any other time, you should follow a list of instructions drawn up by the Severnside Emergency Planning Forum.
Official advice is to:
1. Go indoors and stay there. Do not collect children from school as they will be properly cared for.
2. Close windows and doors.
3. Listen to your local radio. Follow any instructions you are given.
4. Put off any gas appliances, ventilation systems and ensure there are no naked flames.
5. Do not leave the area unless you urgently need help or you are advised to do so.
6. Do not use telephones unless you urgently need help. This will keep phone lines free for emergency use.
7. Stay indoors until you are advised otherwise or the all clear is sounded by the Severnside Sirens.
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