Don't be complacent about this issue Osh. I think you may have under-assessed the risk factor. An office environment is probably classed as a 'normal fire risk'. There are plenty of things in most offfices that can ignite (eg. photocopiers, electric heaters, electric fans, some lighting, flammable liquids, etc) as well as lots of combustible material. In your case you could show some concern about what is stored downstairs and the risk factor of their premises. Can you safely egress from your office if the downstairs floor is burning?
I would recommend Postdog's suggestion to get a proper fire risk assessment carried out by accredited fire safety officers.