Fusion is by far the safest spaceship energy source with our current knowledge (yes, solar is safer as fusion happens far away, but you don't take the sun with you - if you do you have fusion drive again). It is safe mainly because it is such a pain to get the reaction going - so you won't have D+T fuse by themselves in a storage chamber.
(note - I took some liberties in conversion to have nice numbers, but most numbers are fairly close to the correct ones)
Inside the reactor where the fun stuff happens (well, will hopefully happen eventually), you have something like 10g of matter (1) at very high temperature and pressure that is producing energy. D-T fusion gives about 100GWh/kg, so energy content of that little ball of plasma is 1GWh, which is about 1T of TNT. Sounds like a huge explosion, but when the plasma hits magnets, it won't do much fusion - it will simply blast a nice hole in the walls and magnets before expanding and cooling to something non-problematic. Magnets will pop too, but for ITER 10kT of magnets are planned to have only 15MWh of magnetic energy in them - only 15kg of TNT.
That's it, nothing meaningful as far as an explosion goes. Deuterium and tritium (or whatever else the ship is using) won't undergo further fusion without magnets working (and if they did work, it wouldn't blow up in the first place). So the reaction stops as there is nothing to keep it going, D and T that were in storage scape through the new hole.
However, there is a potential problem - the ship might have a lot of oxygen stored somewhere for those humanoids (or other lifeforms). And it might have a lot of fuel to travel far. So, you are in some danger of D/T to make ordinary chemical reaction (= burning, or possibly explosion). If we take say 500T of fuel (2) and enough oxygen, this has potential to release as much energy as the first nuclear bombs, ruins a lot of oxygen and makes a swimming pool of heavy water.
(1): ITER will have 1g for few hundred MW. https://www.nature.com/articles/s41567-020-1023-5
An ITER plasma weighs about a gram, and our fuelling is about a gram
(2): This is comparable to oxygen+RP1 in Falcon 9. https://en.wikipedia.org/wiki/Falcon_9#Pricing