Hi all
I need help with a gas detection design and interfacing it in the entire building i.e aircon shutdown,lift homing,fire detection,fire brigade.pls help

 

Is this really the kind of thing you want advice from random strangers on the other side of the internet who can't see what's going on? This is a really detailed assignment, for which you have given no details and just want "help". There are more safety factors than I could shake a stick at. I suggest you contact a contractor in your area for this project.

 

Is this some sort of homework (?), since it's likely not something that you could legally do without being a licensed installer of such systems.

 

... it's likely not something that you could legally do...

+1 And even less likely to be done safely without serious and specialized know-how.