A worker has died during a non-operational incident, the Ministry of Defence has confirmed.
Cpl Christopher Gill, of 4th Battalion, The Ranger Regiment, died astatine Brecon, Powys, connected 16 October.
Known arsenic "Gilly", helium has been described arsenic a "remarkable Army Special Operations soldier".
"Our thoughts are with his household and friends astatine this bittersweet time," said the MoD connected Sunday.