On every fuel station there's a big board telling us that they will not fill CNG in vehicles which have cylinder older than 5 years. And that according to Pakistan CNG rules 1992 everybody has to get their cylinder tested after 5 years.
I have never seen any fuel station denying filling up of CNG, except a Shell station once asked me, 'your car is looking too old, we will not fill it to tank full level.' after which I indignantly told then that I bought the cylinder new 4 years ago and once 5 years milestone is near, I'll myself get it tested just for the sake of safety.
Anyhow recently I came across a car which had CNG kit fitted since eons and thought of taking it to HDIP for testing. This is mainly because of personal responsibility and general regard of safety.
After all, my family are the ones who sit in this car. Nowadays CNG cylinder is very expensive (main reason being fitting of CNG in diesel buses and trucks, which require 8 or 10 cylinders at a time). A cylinder I bought for Rs. 5000/- in 2007 now costs Rs. 18000/-. Like every Pakistani, I'm also tight on budget these days. But still, I concluded that Rs. 18000/- even though high, is not greater than the lives of me, my family, the person operating the fuel dispenser on the fuel station or other people present on the station during filling up.
That's why I opted (opted, because the regulation is not being enforced even mildly) to invest into Rs. 550/- testing fees, driving my car to a lab far away, taking the time off from office/personal activities to go there and back, running it for 3-5 days on petrol (and getting the petrol system up to mark for this purpose, also costing money) and be prepared to spend Rs. 18000/- + fitting charges if the cylinder fails the test.
Related link: http://www.pakwheels.com/forums/auto...ulted-pakistan
EDIT: Replaced default post icon with little arrow to make OP's posts stand out.
EDIT2: Added link to Pakistan CNG Rules 1992.