Confined space fatality

Two cylindrical foam sponge pads had been inserted in a riser guide tube to form a plug. Argon gas had been pumped into the 60 cm space between the two sponges as shielding gas for welding on the exterior of the riser guide tube. After completion of the welding, a worker descended into the riser guide tube by rope access to remove the upper sponge. While inside, communication with the worker ceased. A confined space attendant entered the riser guide tube to investigate. Finding his colleague unconscious, he called for rescue and then he too lost consciousness. On being brought to the surface, the first worker received CPR; was taken to hospital; but died of suspected cardio-respiratory failure after 2 hours of descent into the space. The co-worker recovered.
Source:IGOP