My job is a DSEAR Compliance Manager and I see you state that it is a COMAH warehouse you are working within. If that is the case a Hazardous Area Classification should already exist for you to refer to. This document giving you the extent of the zones present and is what you will be basing your Risk Assessment upon.
You will be trying to prevent the following ignition sources, as your main risk is a fire being started which burns out of control and causes aerosol canisters to start to ignite. Your main sources of ignition hazard to consider are as follows: Hot Surfaces, Mechanical Sparks, Flames, hot gases, Electrical sparks, Stray electric currents and cathodic corrosion protection, Static electricity, Lightning, Electromagnetic waves, Ionising radiation, High frequency radiation, Ultrasonics, Adiabatic compression and Chemical reaction.
Each should be considered in turn most can be ruled out straight away. Ensure that all electrical equipment located within any potential zones is ATEX rated and the Temperature rating of the equipment is within for the safe range of the Lower Flammable Limit for the substances being stored.
As for courses Health and Safety Laboratory (HSL), BASEEFA, SIRA and IECEX all run Hazardous Area Classification Courses.
The risk assessment will also cover things like maintenance schedules as per the equipment manufacturers Literature and BSEN660079-17 Explosive atmospheres Electrical installations inspection and maintenance.
All electrical installation, inspection and maintenance works are to be carried out by Compex or IECEX qualified Electrical Engineers. Mechanical installation, inspection and maintenance works are to be carried out by Compex qualified Mechanical Engineers.
On some of the COMAH sites we have had to allow for Fire in adjacent Businesses, Sabotage, Vandalism, Arson, Theft, Unauthorised Access, Subsidence, Flood, Aircraft Crash and Human Error. As you can see there is quite a lot to be assessed. And this is a very brief overview.
If you think that is over the top it is some of the elements which would be expected for a COMAH Location.
I hope this helps somewhat as to what you are after.