COMAH public warning alarm

In the unlikely event of an emergency on our site which could affect the local community, a high siren will sound. This siren is much louder than our regular on-site alarms and can be heard over a wide area. If you hear this alarm at any time for more than a few seconds, please follow the public safety instructions in this leaflet.

At the same time, we will activate the off-site emergency plan as described above.

Go in  Stay in  Tune in

In the unlikely event of an incident, the COMAH siren will be sounded. Please familiarise yourself with the alarm sound by clicking the button below.

Play sound

If you hear this alarm, please follow the procedure set out below:

​ Go in: Go to a safe place

Go indoors.  Do not leave your home or work or go outside.  Local schools, nurseries, homes for the elderly and vulnerable and other community facilities will be prepared for this situation. 

​ Stay in: Make that place safe

Close all outside doors and windows, as well as any other ventilation.  Switch off gas appliances and do not light matches.  Move away from windows.

​ Tune in

Switch on a radio and tune in to BBC Three Counties Radio on 95.5 FM, 103.8 FM, 104.5 FM or DAB Herts Beds Bucks.  Listen for any announcements.  Follow any instructions provided by the Emergency Services. 

Do not phone the JM site or the Emergency Services unless you are injured or hurt. Lines need to be kept free for communications.

All clear

Wait inside until the ‘all clear’ is given or you are given other advice. Messages giving ‘the all clear’ will be issued by the Emergency Services or local radio.

Play sound


Further information and contact details


Call us: 01763 253091

Email us

The information in this page is important. Please download our safety leaflet and keep or display it in a safe place. Ensure that everyone in your address is aware understands what actions to take in the case of an emergency.


For further information about our site:


For further information about COMAH, please contact:

Johnson Matthey in Royston

Johnson Matthey (JM) is a British company with operations across the globe. Our origins date back to 1817 and our headquarters have been based in Royston since the 1950s. Hundreds of people are now based at our site in Orchard Road.

Throughout our long history, we have used our leading science to solve our customers’ problems and our science is at the heart of countless products and services that the world relies on. For instance, our teams around the world produce important catalysts and chemicals that enable the world’s food and energy supply chains – and a lot of this is done in Royston. 

Royston is also one of our key sites for our Clean Air business. Here we research, develop and manufacture a range of important catalyst products that help the automotive industry reduce harmful emissions from all types of vehicles, saving thousands of lives around the world by making our air cleaner.

One of JM’s values is protecting our people and the planet. This extends to the communities in which we operate. As Royston is home to our headquarters, the Royston community is important to us.