Gringo, thanks for the question.
Here in the states, and very clearly in the International Building Code, the use of anything besides rigid metal duct is disallowed. The use of PVC has been controversial in several matters: burn ability, condensation buildup, etc. but we do not hear of its use currently in new construction. I do not see why PVC would keep the lint from catching fire. There are lots of versions of the aluminum foil flex. some, mostly few, have the real UL fire testing approval stamps. Some of the stuff I've seen, is very flammable.
Not that I am plugging my product, but I've been in the business for 15 years, and the product we sell: DryerFlex, is a very impressive product. There have been other technicians that have run tests on this flex, and came out with the same impressed mood. DryerFlex is the only flexible duct that has met all the code requiements and flammability tests. Enough said, sorry.
Gas dryer sparking, I am not sure why. could be some of the debris that made it past your lint screen and clung to the pipe walls, and created this reaction, perhaps some sort of chemical reaction. Or it is melting the flex, and the popping is the layers of flex expanding and creating air pockets exploding.
Building codes in the US require rigid pipe in any concealed space (walls, attic, and crawlspace). Make sure your termination hood is not blocked and is not the type that does not open 100%, and where the opening is not smaller than the pipe opening. hope this helps. Thanks.
