The answer is "Yes" if the dryer vent is connected to a gas water heater, but it isn't connected to a natural gas line. This can happen in homes where natural gas was used exclusively before, and there has been no upgrade to the appliance connections to allow for the use of propane or an electric-powered dryer. If you are using a gas-powered dryer, it is important to ensure that the venting is properly vented to the outside. If there are any obstructions in the vent path (such as kinks or elbows) this will cause the vent to become heated, and once hot enough, you're flammable gasses can ignite.