Tires: When to replace a tire, flammable material, tire industry

Question
Hi Barry:
       I have been told that no matter what the tread debth, if a tire shows dry rott cracks down in the carcass of the tread it's time to replace them.  Is this true?  Let me say that I am reffering to 10.00 / 20 tires on trailers that carry very flammable material such as hydrogen.

Answer
Patrick,

Not only is it true, but the tire industry is publishing bulletins that say that there is a time limit REGARDLESS of what the tire looks like or how much it has been used.

So if you are carrying a flammable substance, then you should be replacing the tires more regularly than normal.  You should be working closely with a trustworthy tire dealer who has a stake in your success.