Can I use the aggregate rating or two extinguishers to determine adequate extinguisher coverage?

[Hayfever]

A 150m2 hairdressing salon is covered by a 6l AFF and 2kg CO2 by the main entrance (exit). There is no extinguisher by the rear exit 

It's time to upgrade and I am considering advising 2 x 2l water spray P50s - one at either door.

As they are both rated at 8A, if I can use the aggregate 'score' of both extinguishers, there is plenty of cover as I only need <13A

 

But can I add up the ratings of two smaller extinguishers like this at a very small and low risk retail outlet?

 

[AnthonyB]

I've answered this in another forum for you - in essence yes, but for larger areas than you are covering it is cautioned against using a small number of very high or a large number of very low rated units.

 

A 661 sq.m. building would have a floor rating of 43A. A single 43A rated powder or high performance water additive would meet this as would 9 x 5A rated Powders but for the best balance of individual unit fire fighting performance and distance of travel to get to the extinguisher (without putting the fire between you and the exit) you might be better with 4 x 13A units.
They don't all have to be the same - you could also use 2 x 21A rated units and an 8A rated unit, the combinations can be endless the larger the area!

[Hayfever]

Many thanks Anthony