Ahem...as a professional corporate trainer, book author (The eFactor, search Amazon) as well as a firefighter and secretary of the fire company, I do more than my share of writing in a variety of situations.

Basically, for instructional communications (that's what you're doing with emergency instructions) you use a rather terse, clipped language, and if it's really important don't leave room for any interpretation.

WRONG: If there's a smell of fuel near your crashed plane, don't light a fire anywhere near it.

RIGHT: No open flame near the plane if fuel is spilled.

Similarly, numbers take up less space and are unambigous. Thus:

WRONG: When ventilating a room using hydraulic methods, ensure that your fog spray fills eighty to ninety percent of the window.

RIGHT: For Hydraulic ventilation, use a fog spray to fill 80% to 90% of the window.

The best instructions are printed right on the toor or equipment to be used. I have an old beat-up Ford F-250 that I loan out to lots of people. It's loaded with labels for the untrained:

PRESS CLUTCH HARD TO FLOOR BEFORE STARTING
GET FUEL IMMEDIATELY IF GAS GAUGE MOVES
CHECK OIL WHEN GETTING GAS
TO REMOVE KEY PRESS BUTTON ->