Two World War Two re-enactors suffered leg injuries when an explosives demonstration went wrong.
It happened during an English Heritage event at Audley End House, near Saffron Walden in Essex on Monday.
They were taken to hospital but their injuries are not thought to be life-threatening, as Essex Live reported.
The incident is being investigated by English Heritage and Jamie Osborne, general manager of Audley End House, said: “Our thoughts are with those injured.
“With all of our events, but especially an event of this nature, we have strict safety controls in place but clearly something went wrong and we are investigating what happened.”