The state Fire Marshall’s office is tracking not only the number of fires that destroy property, but the number of house explosions in Iowa. The office recorded an average of 20 each year from 1994 to 1999, and a slow but steady increase in the number ever since, to 37 per year. Fire prevention inspector Jeff Miller says there were three home explosions linked to gas leaks just in the last month. He says the main cause of an explosion is usually related to gas — heating equipment, liquid propane or natural gas, piping leaks or the malfunction of equipment. In a recent case in Eldora, investigators say a homeowner trying to light the water heater sparked an explosion. The Fire Marshall concluded that a faulty valve was to blame. Miller says natural gas is mixed with a chemical that gives it a distinctive odor so it can be detected. It smells like rotten eggs. Miller says people should be aware of what kind of system their home has, and if they smell gas they should take precautions like putting out any open flames and smoking materials and getting out immediately. Miller says sometimes the smell of gas can fade, absorbed into building materials or soil, so it’s important to have your furnace, water heater or other gas appliances checked regularly. By Iowa law, you should have a trained professional install gas systems. Miller says you should also have any repairs done by a trained professional