Why does Cutter use a fireaxe to save a trapped performer in the water tank trick?

In The Prestige (2006), a major plot point early in the film is

Julia's death during the water tank escape trick.

Each performance, Cutter stands offstage with a stopwatch and a fireaxe to break the water tank in case Julia is taking too long to escape. But why is the fireaxe necessary? As shown later in the film

the water tank has a trick lock that can be opened without a key. A hidden slot in the tank allows the "trapped" performer to access the lock after they have slipped out of their restraints. The trick lock can be easily accessed by others on the outside of the tank.

This fact resurfaces at the end of the film:

When Borden sees Angier in the water tank under the stage and Angier starts to drown, the first thing Borden does is attempt to open the trick lock, only to realize it is not a trick lock this time! Only then does he yell for the key. When he realizes there is no key, then he tries to break the tank with a wrench.

The fireaxe seems to be a completely redundant and less effective means of rescuing a trapped performer in the water tank. If Cutter was worried about revealing the trick to the audience, then he could just as easily

carry a fake key for the trick lock.

So why does Cutter use a fireaxe to save a trapped performer in the water tank trick?

Trick locks can malfunction, maybe in a manner which makes it hard to quickly break them open. Lids may jam. An axe capable of breaking the glass is the ultimate backup solution.

What do you have to do if you don't use an axe? You would have to open the trick lock and climb a glass box taller than you, to open a lid and then drag a potentially unconscious person out of a water tank when balanced on the walls. Even with the help of other people, this doesn't sound that easy when seconds count.

Yes you might have a step-ladder to hand to help as well, but even then I don't think I could easily reach down into a deep tank with someone slumped in it unconscious and pull them out.

You might also use the hoist that was used to place the person in the tank in the first place, but that would require coordination and would still not be an easy job to attach them to the hoist if the person was unconscious or even just panicking.

An axe capable of breaking the glass and draining the tank sounds like a good solution to have at hand for emergencies.

(this point has been made by others in comments)

I can't remember if the axe is visible before it is obvious that Julia is in trouble, but if it is, the axe is also a piece of showmanship. It emphasises how dangerous the trick is.

Personally I think a pickaxe or sledgehammer is likely to be more effective against the glass, but I would want something to be available if I was performing this.