When seconds count, the police are only minutes away. I would seriously consider alternatives, perhaps with a code or biometric safe that keeps any kiddos out of it.
If you have been reduced down to figuring out how to make a fire extinguisher into a self defense weapon, then I would suggest considering the following.
Get a medium dry chemical fire extinguisher with a hose. (~$40 at Costco). Fashion a cone shaped "sprayer" similar to the brass sprayer cones for garden hoses. So it will spray a stream vs. a wide spray. But you know what, on second thought, I'd go with a smaller one that you can wield one handed. Stay with the dry chemical, and aim for the face, and keep your other hand free.
A fire extinguisher does not just have one 'woosh' and it's over. The squeeze valve on top can be released and squeezed again as long as you havn't depleted the powder charge. So you could potentially have several short "shots". IF you can get it in the assailant's face, (without getting shot or stabbed yourself) then there is a good chance they will breath in a blast of it, and get it in their eyes. If you can manage this in the dark, then excellent, you've given yourself the advantage, and, by coincidence you are now holding a large metal club. It would really ruin someone’s day to be hit in the head with a metal fire extinguisher by a crazed adrenalin filled homeowner in his underwear.
If firearms are completely out of the question, consider a "decorative katana sword", the damage even the $20 ones can do is unbelievable. Still no good? Keep some bear spray on hand "in case you go hiking". Yeah, indoors your eyes will burn some too (but not like the bad guy's) and slightly burning eyes is better than dead. I'm sure you have kitchen knifes? A chef's knife can work in a pinch. Get creative.
Otherwise, if you are married to the queen of all pacifists, and all of the above is out… Then re-enforce the hell out of your bedroom door and door frame. Equip it with some manly locks and hide out until help arrives. If you are allowed no offense, then go defense.
If you have a modern alarm with zwave, get a battery powered deadbolt for the bedroom door, and set it to lock if the alarm goes off. That way your bedroom door is secured automatically if the alarm sounds. (not so useful though if you have kids though and need to protect them)