Opinions are provided with the understanding that AFSA assumes no liability for the opinions or actions taken on them. The obvious answer is when you have freezing temperatures. There are two criteria driving the need for a dry-pipe system. One criteria is that the system is subject to freezing. The second criteria is maintaining a temperature of 40 degrees Farenheit.
Many people mistakenly assume failing either criteria requires a dry-pipe.
Since NFPA 13 does not identify what areas are subject to freezing, it does not tell you when to provide the protection. As most everyone is aware, the year 2000 poses some potential problems for computer systems. As you know, the majority of sprinkler systems do not contain computers or micro-chips as part of the system. These systems have no potential for such a problem. There is one type system, that being those with deluge valves, which can incorporate micro-chips.