Grant Lobdell is the Senior Chemist and Lab Manager at Dyne Fire Protection Labs. His article Ensure Your Antifreeze Solution is in Compliance with NFPA 25 was published in the September edition of FPC magazine. 

Excerpt from the article:

Determining the type of antifreeze solution present and making sure it is within acceptable concentrations is critical —not only to make sure it prevents system failure due to freezing but also to ensure the solution doesn’t become a fire hazard itself. When sampling antifreeze solution for annual testing, NFPA 25 recommends a sample be taken from the top and bottom of each system. Additionally, NFPA 25 requires samples be taken at the most remote portion and the water supply if they are not located at the top or bottom. If the system is greater than 150 gallons, there must be an additional sample taken for every 100 gallons of antifreeze solution.