How to avoid leveling up while training

I'm a late gamer of Fallout Shelter, but I've already read tons of threads around about most of the game aspects. I know that before leveling up a dweller is better to train his/her endurance to the max to further improve their HPs.

My question is: how to prevent them from gaining exp from random events like radroach infestation or fire? I have 3-4 level 1 dwellers training, and it's already occurred a couple of times that a fire bursted out in a room where I didn't have any dwellers to take care of it. It spread out. I managed to move 2 of these fresh dwellers to another room and when the fire has been extinguished they didn't earn any XPs. You do understand I can't move them around every time it happens.

And I know the dweller won't level up until you tap on the arrow, but how do you deal with the training arrow meanwhile? It doesn't show up if you don't let him/her level up first. I thought the respective arrows would've appeared together, that you you could've tapped only the one you needed. But it's not. I just experienced it with one dweller who had to go level 2, and she was training strength. Above her head there was the "ready" text, but only the level arrow was bumping. Once I tapped it, I was able to tap the training arrow to make her proceed with the training.

You got any workaround for this? I don't know if this question has been already posted, I couldn't find anything related. And I hope I made myself clear.

Thank you in advance.

You must tap the appropriate "level up" arrows in the order that you received them. As noted, a vault dweller will only display one "level up" arrow at a time.

In this case, if your vault dweller levels up their character before leveling up their SPECIAL skills then that is the order that you must advance the character. Vice versa, if you lock your character in a training room and they never encounter a situation which awards them XP then they can safely level up all of their skills before leveling up their character.

Since being awarded XP is what levels up your characters you'll need to do your best to limit situations which could give them XP:

• Don't send the vault dwellers you wish to train out into the wasteland, and don't make them guard the door to your vault - both situations they'll risk encountering enemies which provide XP when killed.
• Avoid placing them in rooms which are adjacent to dirt. Pests like Mole Rats and Radroaches can only attack rooms that are next to dirt. This means a training room surrounded by other rooms from all four sides cannot be the first target from a creature attack. Pests in adjacent rooms can spread to a fully-surrounded room if allowed to spread unchecked
• Avoid "Rushing" production rooms. When a "rush" is failed a crisis occurs. This can mean a fire spreads or a pest attack occurs, both of which award XP to dwellers who resolved the crisis.

Unfortunately, there isn't a way to completely prevent your vault dwellers from encountering a situation that can award XP as a fire can start in any room, and awards XP when extinguished. You'll just have to move the vault dwellers you wish to train to another room for the duration of the emergency.

Since it can't be mitigated entirely, I'd recommend only training one our two vault dwellers at a time as "pure" endurance dwellers. The rest would be have endurance-focused training in which they resolve crises as needed but train the rest of the time. While it isn't 100% optimal, it's a lot less of a headache to move the two "pure" endurance dwellers to another room to avoid an XP-awarding situation than to move ten dwellers.