He must be a damn old off duty fire fighter. An expert witness could run rings around him in court with regard to competence.
Obsolete sizes, no A-rating floor calculations, he is clearly incompetent when it comes to specifying PFE (& I can say that with no fear of his lawyers- bring it on!).
He is taking a premises with adequate cover and throwing their cash down the drain in order to install non existent extinguishers, when I would bet that the existing cover works out adequate and just requires ongoing maintenance.
I wouldn't let it drop - I'd get his details and pursue the matter, his employer wouldn't be too chuffed. Best way of getting you believed - get a real genuine up to date fire safety enforcement officer down: an on duty specialist trumps an off duty amateur (which he is as he is a professional fire fighter, not a professional FPO)
Foam extinguishers, prior to BS5423 & BS 5306-3 (& the fire rating scheme) in the early 80's could not be specified for Class A risks if the codes of the time were followed as they were not deemed the most suitable or efficient - remember in those days you still used Chemical Foam extinguishers (which weren't that good for Class B either!) and Foam branchpipe extinguishers with protein & fluoroprotein foams, although something revolutionary called 'Light Water' from 3M had started to appear in the Pyrene/Read & Campbell/Chubb Group product.
In the early 80's the A rating & new codes meant you could use Foam for AB risk, furthered by the pioneering use by Thomas Glover of AFFF as a non aspirated spray (originally labelled as an ABCE class extinguisher).
Prior to fire ratings and the new BS specs, extinguishers were specified by mass, and standard imperial measurement capacities were used by industry & codes. With the onset of metrification & the new BS, the traditional sizes were retained in metric or changed to Euro sizes. Thus the 1 gallon water size became 6 litres (not the 4.5 litre direct metric conversion), although it was briefly revived in the early 90's with the original 4.5 litre Chubb Hydrospray Elite; 2 gallons became 9 litres and 2.5/5/7/10/15/20 lb Powder became 1/2/4.5/6/9 kilo. CO2 generally metrified with 2.5lb being 1.1 kilo, 5lb being 2 kilo (not 2.2), 10lb disappearing to become 5 kilo. The quirks of maritime specification led to two sizes being retained in direct imperial steel cylinders - the 7lb steel was retained as the 3.2 kilo & the 15lb as the 6.8 kilo. Never was there a 3kilo size.
Expect little contribution on extinguisher threads after tomorrow as I'm away for 3 weeks on hols - hooray!