Right Way Up asked:
Would be interested to know if this airline routinely carries dangerous goods.
I don't know about the accident airline's policies but, given the point of departure, it's possible that dive cylinders might have been on board. Standard precautions / procedures (depressurise the tank and preferably remove the valve - or open it) will prevent any problems but if proper precautions are not taken cylinders can be dangerous as this story shows;
Dive shop explosion sends tank shooting through parking lot | www.kirotv.com
Today's accident occurred near the top of the climb. The higher the pressure altitude, the greater the pressure differential if a dive cylinder has not been depressurised.
Dive cylinders that have been depressurised need to be inspected for corrosion before they can be re-used, so divers prefer to keep them at least slightly pressurised at all times to prevent corrosion. Airlines require dive cylinders to be depressurised before flight. Despite these opposing interests, qualified divers will be aware of the dangers and should respect the rules and airlines should enforce them. As a result, the chances of an accident are low but such an occurrence is not completely beyond the bounds of possibility.
Significant damage was caused to a Qantas 747 in 2008 when an oxygen cylinder exploded. This was part of the aircraft's systems but demonstrates what can happen when pressurised gas cylinders fail on board an aircraft;
"After clearing the baggage and cargo from the forward aircraft hold, it was evident that one passenger oxygen cylinder (number-4 from a bank of seven cylinders along the right side of the cargo hold) had sustained a sudden failure and forceful discharge of its pressurised contents into the aircraft hold, rupturing the fuselage in the vicinity of the wing-fuselage leading edge fairing. The cylinder had been propelled upward by the force of the discharge, puncturing the cabin floor and entering the cabin adjacent to the second main cabin door. The cylinder had subsequently impacted the door frame, door handle and overhead panelling, before falling to the cabin floor and exiting the aircraft through the ruptured fuselage."
Source:
https://en.wikipedia.org/wiki/Qantas_Flight_30
See also;
ASN Aircraft accident Boeing 747-438 VH-OJK Manila, Philippines