According to the Danish maritime weekly SOEFART, 29 June, 2007, the reason for the fire might have been found.
The Danish Maritime Authorities, assisted by the police and "fire technical expertise" have found defects in the fluorescent tubes on sister vessel POSEIDON. A few months ago both ships had new tubes installed of identical type as in the hold of HERCULES in which the fire (in cardboard packing) started. Tests have revealed that the tubes overheated due to "light arcs" in the sockets.
A warning has been issued regarding this type of tubes: "ADVANCE model Centium 1CN-2P32-SC, Instart - start Electronic Ballast".
Br
Niels