Hi padurluc

Your profile indicates that you are in England, so I am a little surprised that you have ammonia refrigeration though there might be good reasons not to have an inherently safer refrigerant.

However in terms of training my starting point would be the relevant Institution.

Technical information Refrigeration Air Conditioning and Heat Pumps (ior.org.uk)

Ammonia is a more efficient industrial refrigerant than traditional CFC "F-Gas" so for operations such as chilled food distribution there are significant savings in operating (energy) costs.

Ammonia is cheaper than F-Gas (many of which are being phased out).

It ticks the environmental check boxes of Global Warming / Ozone Depletion Potential = 0

It is poisonous in high concentrations but so long as copper piping is not used and the system is well maintained there are rarely issues.

One of our industrial neighbours was a chilled food distribution company - it was only after they vacated the site and scrap metal rogues started appearing we got a whiff of what they used for cooling.

Look to BS EN378 and BS EN 13313: Ammonia is used widespread in the UK and is if properly installed and maintained as safe if not safer then the others for the reasons stated before (you can smeel it) and zero GWP, With the phase out of the older refrigerants you now have issues with their repacements i.e. Propane etc and CO2 is also on the rise (high pressures). There are several companies who will train employees for ammona handling  (CITB 2078 off the top of my head) and trade bodiessuch as BESA.

Mark.