MRC Internal siren tests


Contra Costa County Community Warning System

MRC Internal Siren tests

The refinery runs internal tests Mondays between 11:00 am and 12:00 pm to ensure our sirens are operational. During the tests on Monday, sirens will typically be heard by our fence line neighbors and potentially beyond. Testing our sirens ensures we run the refinery to the highest safety standards possible to protect the community, employees, and contract partners.

We have a team of dedicated employees who respond to inquiries 24 hours a day, seven days a week. We invite our neighbors to call our Weekday Phone number at 925-313-3777 or our After-Hours Phone number at 925-313-3601.


The Contra Costa County Office of the Sheriff operates the Community Warning System and their website states, “Sirens are tested on the first Wednesday of every month at 11:00am. For the remaining Wednesdays, a more quiet and low “growl” test is performed at 11:00am”.

You can register to receive Community Warning System alerts at

CWS Levels

Contra Costa County maintains a community warning system (CWS) to keep area residents informed during various community incidents that have the potential to impact residents.
cellphone in hand displaying alert app on screen

Level 1

Notification only. Not expected to have off-site health consequences. No community action required.

Level 2

Hazardous materials release, or potential release, expected to have off-site consequences or possible adverse health consequences. Sensitive populations (children, elderly) should limit outside activity.

Level 3

Hazardous materials release, or potential release, expected to have off-site consequences with potential adverse health consequences for the general public. All residents should shelter-in-place and await instructions from City and County officals. CWS sirens are activated.