Around here you (the patient, with assistance from a staff member) makes a safety chart/plan/pyramid/traffic light/..

The simplest one has 3 levels: red, orange/yellow, green.
For every colour it lists:
- What happens during this colour?
- What should I do now that is helpful?
- What should/can another person do now?
Depending on the person's specific struggles, he might also add a line or two that indicates he's in a certain colour (e.g. muttering to self = yellow in my case)

The chart can be used for any issue at all: panic, anxiety, flashbacks, sadness, anger, urges.
And also for longer-term issues as a way of relapse prevention: not showering every two days might mean orange, when depression is the problem.

I actually have 3 - one for trauma-related panic (meaning flashbacks and severe triggers), one for escalating anxiety (basically meaning tension, or arguments with any person with authority (that really scares me)), and one for acute panic (basically meaning over-stimulation).
Adding everything to 1 chart just wasn't practical for me. Although most people only have 1 - or 1 for acute and 1 for relapse prevention.

It's been very helpful to me because it tells me what I can do to help myself (and it also gives me permission to do so!) and also how the staff etc will most probably act. One of the scary things about any loss of control through emotions, is that you can't control how other people will react to it - you don't know what to expect. Which will cause even more anxiety. Which doesn't help.
But now I know how others are most likely to (re)act, that means less stress - and also allows me to seek help more easily.

I summarized my plan for school and added a line on acute hopelessness/self destructive urges. I know now that if I ask for help in that area, they will - as instructed - find me a place to sit (that's semi-public) and ask me to agree to stay there until the urge has passed.
This means I can ask for that help: they won't require me to make promises I can't make (such as: not hurting myself) and would only lead to stress and noncooperation (I don't make promises I can't keep, so I would panic if it's required of me), they won't overreact ("hand in your bag empty your pockets and sit next to me until you feel better") and they won't do the wrong thing (put me in a room by myself with a door I can close).