Exercise 6. Read the text B Phases of Burning

Once combustion takes place, a fire in a confined space will typically progress through several distinct phases. Some authorities list three phases; others recognize four. All agree on the first two phases, called incipient phases and the open-burning phases (sometimes called the “free-burning” or “steady burning phase”). The third phase, or smoldering phase, is sometimes divided into two separate phases.

First phase. The first phase is the incipient phase or beginning stage. In this stage, the fire is just beginning to burn. Oxygen inside the room is at normal level (21% of the air). With this amount of oxygen, the flame burns brightly and combustion is nearly complete. The basic products of combustion during this phase are carbon dioxide, water vapor, and a small amount of carbon monoxide. Depending on the room contents, other gases may be produced. The temperature of the fire’s seat may rise to about 10000 degrees F (540 degrees C), but the ceiling temperature will rise only slightly at first. Visibility is not a problem, and can usually be accomplished by merely opening a window or a door. The fire can be easily extinguished.

Second phase. The second phase is called open-burning phase. Oxygen in the room is reduced below the normal level, down to a point in the range of 16 to 19%. As a result of this lower oxygen content, the flame doesn’t burn as brightly, and combustion is less complete. The room begins to fill with smoke, and the carbon monoxide level increases. Ceiling temperatures begin to rise dramatically, and can reach 700 degrees F (371 degrees C). Heat accumulates and begins to bank down from the ceiling to the floor levels. Conditions can become dangerous for firefighters very quickly: flashover can occur as the room’s contents reach ignition temperature and burst into flame simultaneously. To survive, you must be wearing breathing apparatus in a burning building. Extinguishing this fire is possible with quick action.

Third phase. The third phase is called smoldering phase. In this phase, oxygen content in the fire area is reduced to approximately 15%. The flames are barely visible, and smoke is dense and becoming darker. The increasingly incomplete combustion produces larger amounts of carbon monoxide and other flammable toxic gases. Temperatures throughout the fire area are very high and dangerous.

Fourth phase. In the fourth phases, a continuation of the smoldering phases, the oxygen level is 13 % or slightly lower. No flame is possible in this oxygen-depleted atmosphere. Smoke is extremely dense, and the carbon monoxide level continues to rise. The ceiling temperature is up to more than 1200 F (649 C). The high temperature drives off flammable gases from the wood, paint, fabrics, chair stuffing and nearly everything else in the room.

Two sides of the fire triangle are now complete: there is plenty of gaseous fuel, and the material is heated well above ignition temperature. The potential for a backdraft explosion is present if the necessary amount of fresh oxygen is improperly introduced to the room.

Exercise 7. Say if it’s true or false.

1) The third phase is called smoldering phase.

2) In the first phase he flames are barely visible, and smoke is dense and becoming darker.

3) The second phase is called open-burning phase.

4) The first phase is the incipient phase or beginning stage.

5) To survive, you must be wearing a fur coat in a burning building.