Teachers have been sitting on a powder keg for years.
We are sitting on a powder keg of outdated nuclear installations.
It is a powder keg waiting to blow—an accident waiting to happen.
If we block this prospect, we shall be storing up a powder keg.
We are living on a powder keg, so far as the debtor countries are concerned.
It would be taking a match to the powder keg that is the middle east.
We will be sitting on a powder keg if some serious action is not taken.
The expellees would otherwise become a potential social and political powder keg, the source of 'political and economic' unrest.
