Has anyone been involved with this? we a several large warhouse office type locations, all use as most modern buildings would, air ducting to deliver both cooled & heated air, I have noticed there are no inspection hatches anywhere to check residue build up. Our maintenance guy seems to think that as air is filtered there is no requirement to check this. Certainly thuogh if there is a build up of dust and crud with air passage it would become an ideal fire travel route. Just though id get the thoughts of others on this. Many Thanks