It is true that fire is very useful to us but it can also be a "bad master" if it gets out of our control. When a fire gets out of control thousands of shops and homes get damaged, vast areas of forests are also devastated and hundreds of people are injured or killed. If fire causes so much of devastation to the environment and to the mankind then it can be considered as a "bad master" because it does whatever it wants and it becomes really hard to get a control on it.