to separate the oxygen in the air from the fuel. carbon dioxide, halon, or sodium bicarbonate can be used. In the case of very small fires and in the absence of other extinguishing agents, covering the flame with a fire blanket can eliminate oxygen flow to the fire. A simple and usually effective way to put out a fire in a stove-top pan is to put a lid on the pan and leave it there. Tactical ventilation or isolation of the fire One of the main risks of a fire is the smoke; because, it carries heat and poisonous gases, and obscures vision. In the case of a fire in a closed location (building), the following two different strategies may be used: isolation of the fire or ventilation. Paul Grimwood introduced the concept of tactical ventilation in the 1980s to encourage a better thought-out approach to this aspect of firefighting. Following work with Warrington Fire Research Consultants (FRDG 6/94) his terminology and concepts were adopted officially by the UK fire services, and are now referred to throughout revised Home Office training manuals (1996–97). Grimwood's original definition of his 1991 unified strategy stated that, "tactical ventilation is either the venting, or containment (isolation) actions by on-scene firefighters, used to take control from the outset of a fire's burning regime, in an effort to gain tactical advantage during interior structural firefighting operations." When properly used, ventilation improves life safety, fire extinguishment, and property conservation by 'pulling' fire away from trapped occupants and objects. In most cases of structural firefighting, a 4x4 foot opening is cut into the roof directly over the fire room. This allows hot smoke and gases to escape through the opening, returning the conditions inside the room to normal. It is important to coordinate the ventilation with an interior fire attack since the opening of a ventilation hole supplies more air, and thus oxygen, to the fire. Ventilation may also "limit fire spread by channeling fire toward nearby openings and allows fire fighters to safely attack the fire" as well as limit smoke, heat, and water damage. Positive pressure ventilation (PPV) consists of using a fan to create excess pressure in a part of the building. This pressure pushes the smoke and heat out of the building, and thus facilitates rescue and fire fighting operations. It is necessary to have an exit for the smoke, to know the building