About Heat Packs
Many people have a false impression about the use of heat packs when shipping coral frags. Heat packs consist of iron powder, charcoal, salt, vermiculite, and water. They generate heat via the oxidation (rusting) process. This can only occur in the presence of oxygen. I ship frags in a cardboard box with all the edges taped shut. Inside the cardboard is a plastic trash bag to prevent any leakage that may get the box soggy and Styrofoam pieces cut to fit inside the box for insulation. There is no way oxygen from outside the box can enter once it is sealed. Once the heat pack consumes the oxygen that was in the box when it was sealed it cools off. That’s the simple truth.
Heat packs are available ranging from the 6 hour hand warmers to some that will last up to 30 hours. I think the ratio of ingredients is how this is achieved. The hand warmers get hotter than the long lasting ones. This is absolutely not what we want when shipping frags. These things can get over 110 degrees. I always use the longest lasting ones I can find. I conducted tests on two boxes containing bags of water packed like I pack them to ship. One box had one of the commercially available heat packs sold for shipping livestock and the other had a long lasting heat pack from WalMart. Each box had a digital thermometer inserted through the side so I could monitor the temperature. I kept a log of the temps for 24 hours. I moved them from inside to outside and then back in. Within an hour of being packed both started cooling off to ambient temperature. There was no difference.
Heat packs would be ideal for shipping something like reptiles where there would be air exchange between inside and outside. The best protection for coral is a well insulated box that prevents air exchange with the outside and having the box held at FedEx for pickup.
Sometimes the people I ship frags to tell me that “the heat pack was still warm”. I ask them if they checked it as soon as they opened the box. Invariably they opened the box and laid the lid aside, picked up the bags and admired their new frags, and began the acclimation procedure. Some time later they start to clean up the shipping supplies and notice the heat pack. They feel it and “it’s still warm!” Nope, it’s “warm again” after being exposed to oxygen.