Let me emphasize once again that INDIVIDUAL letters to the Russian authorities are more effective than collective petitions (although these are also useful if published as open letters). Many of them have bureaucratic guidelines which oblige them to respond to every letter individually, and statistics showing how many letters they have received. (Having worked with such letters in a Soviet-era archive, I can assure you that this bureaucratic rule is indeed a non-negligible counterweight to bureaucratic cynicism.) To be entirely honest, I don't know what their rules are on letters from foreigners, especially in languages other than Russian, but I would assume these might actually carry GREATER weight.
If at all possible (and I know it may be expensive), please send your letter by registered mail. You might want to write to the Russian ambassador in your country in addition to some of the Russian addresses mentioned in this link:
Here and here are detailed instructions (in Russian), including points you might like to mention, sample letters, and an expanded list of addresses.
1. Say who you are, write what has happened with the EUSPb.
2. Say that the EUSPb is a renowned scholarly institution and that the international scholarly community is very concerned.
3. At the moment the EUSPb is unable to function (its license has been suspended) because of the fire safety measures.
4. The university is prepared to meet the demands of the fire safety inspectors as far as possible, but it should be allowed to continue to function.
5. Ask the authorities to lend their support to the university.
6. IMPORTANT: Please include a formal request for a reply, stating your address (private addresses seem to work best).
And finally, please don't forget that it's counterproductive in such letters to lambast the 'evil Russian regime'. The point is to put enough pressure on the authorities that they will find a face-saving solution to restore the university, not to provoke them into making it a point of honor to keep it closed.
PS: If someone wants to draw up a list of relevant Russian embassies, or other addresses specifically relevant to letters from outside Russia, I would be happy to post it on this site.