For reference - the RAF operated a number of barrage balloons as part of the paratroop training process from the 1940s up until (IIRC) 1995. I vaguely recal they were based at RAF Hullavingdon (then a satellite field for RAF Lynham). These balloons were always hydrogen-filled because helium (a) gave less lift and payload, and (b) was simply unaffordable. They simply recognised the risks of using hydrogen and developed operating procedures to mitigate them. I don't *think* they ever had a hydrogen accident, but I could be wrong on that.
One reason the kite balloons used hydrogen, was that they were only inflated when needed; thus avoiding the need for expensive hangarage*. The technology used to ensure safe operation had been learned and passed on from when the Royal Aircraft Establishment at Farnborough was the Kite and Balloon Factory. Mechta Senior worked for the MOD(PE) auditing the various suppliers for the balloon equipment. A problem in later years was the non-static hemp rope of the right gradewas becoming unobtainable, as growing it was banned in the UK as it was considered a drug, whilst other parts of the EU received grants to grow it!
*Kite balloons for human parachuting were taken and inflated where needed. Some used for parachute testing were kept inflated at Cardington in the Airship hangars.
16024, I did ask the people at Hybrid Air Vehicles about using a non-flammable mix of hydrogen and helium. The view was that the hydrogen would migrate to the top of the envelope creating a more dangerous environment there. I also asked about an inner envelope full of hydrogen surrounded by the helium outer envelope. The problem here is that all the cabin/payload suspension cables would have to pass through it, creating sealing issues and extra weight, thus negating the benefits.