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Preparing for the unlikely event of a blackout at CERN

While a blackout this winter is unlikely, CERN is prepared. Here’s some information about what you should do if CERN’s energy supply is cut.

In response to the ongoing energy crisis in Europe, CERN has examined a range of potential scenarios that could occur at CERN over the coming winter. These include the unlikely event of a complete blackout on all sites, which would arise only if both the French and the Swiss electricity supplies were cut off at the same time. If this were to happen, CERN’s diesel generators can provide emergency electricity, but this would not be sufficient to keep everything running. Each department has therefore put in place plans for dealing with a blackout, which have consequences for everyone working on the CERN sites. If this concerns you, please take a few minutes to acquaint yourself with the key points below.

First and foremost, please keep in mind that CERN’s sites are intrinsically safe. Therefore, although most systems at CERN depend on electricity, a blackout is not a cause for alarm. If you are working underground, you should evacuate to the surface as soon as possible, after ensuring that any equipment you may have been using is left in a safe state.

Information, including the time of the start of the blackout, will be provided via CERN’s mobile phone network and by email. Direct wired or wireless internet access is likely to be unavailable, but the mobile phone networks will continue to operate for up to two hours on the CERN sites. Although the Drupal web servers will not be running, it is planned that a simple web page will be available at home.cern, giving basic information about what you should do. Please note that Mattermost is unlikely to be available.

Leaving the sites will understandably be on everyone’s mind if a blackout occurs during working hours and lasts more than 30 minutes. Nevertheless, unless you have pressing reasons, such as picking up children from a crèche or school, please do not leave immediately.

If you are working on the Meyrin site

Access card


In order to ensure a smooth flow of traffic, if you are not required by your department to remain on site and are leaving by car, please do so according to the table below, based on the last digit of your CERN Person ID number, as shown at the bottom of your access card. Jo Public, for example, should leave the site 35 minutes after the start of the blackout. When leaving, please ensure that any equipment you are responsible for is left in a safe state.

Gates A and E will be open for vehicles leaving the CERN site, while gate B will be open for entering the site. All the other gates will be closed to allow the security agents to be deployed at the other gates on the other sites.


When (min) Who (last Person ID digit)
0 to 30 Anyone needing to leave the site for urgent reasons
30 0
35 1
40 2
45 3
50 4
55 5
60 6
65 7
70 8
75 9


If you are working on the Prévessin site

Those whose Person ID number ends with the digit 0, 1, 2, 3 or 4 should leave no earlier than 30 minutes after the start of the blackout, while those whose number ends with the digit 5, 6, 7, 8 or 9 should leave no earlier than 40 minutes after the start of the blackout.

If you are working on any other site, you may leave at your convenience if electricity has not been restored within 30 minutes.

Pedestrians and cyclists

Bicycle turnstiles will not be powered, so cyclists will have to use the car lanes. On the Meyrin site, they may use gates A, B or E but should be aware that traffic through gate B could be disrupted if the blackout affects the traffic lights.

Pedestrians leaving the Meyrin site may use gates A, B, C or E, as well as the Jura turnstile gate close to Building 33. It will not be possible to leave via the CERN reception area in Building 33.

Further information

A document containing full details of which services will be maintained, drawn up by the SCE department, is accessible on EDMS to anyone with a CERN account. A list of the services that the IT department expects to keep running can be consulted here. In the event of a blackout, up-to-date information on which services are actually running will be available on the IT service board.