Does anyone know how long the US government can seal records for?

By way of explanation... Say something happened in 1999 but that full disclosure of events was not deemed to be in the public interest and the intelligence agencies decided to cover things up. Would the records of said event be released in full at a later date, say in 30, 50 or even 100 years later?

Also, can records be sealed for longer than a standard number of years? For example, because people involved at still alive?

Hope that is all clearer than mud.

Any light anyone could shed on this would be gratefully received! smile

Thanks,

Chris