REVIEW OF SMOKE IN A BUILDING

If you want know about Smoke movement in building or General exit requirements or Auditorium design or Lighting design or Principles of design please click the link above.


  • In a high-rise building, the stairs typically represent the sole means of egress during a fire.
  • It is imperative for the exit stairs to be free of smoke and to incorporate design features that improve the speed of occupant egress.
  • Most building codes require the fire stairwells in a high-rise building to be pressurized to keep smoke out.

1) Review of smoke

i) Hazards of Smoke

Smoke contains toxic and irritant gases.

  • ¾ of all fire deaths are caused by smoke inhalation.
  • Approximately 57% of fire deaths occur outside the room of fire origin.
  • 47% of fire survivors could not see more than 12’.
  • Smoke travels 120 to 240 ft./min.

ii) Smoke Management

  • A smoke management system includes all methods described below singly or in combination to modify or influence the smoke movement.
Limit the fire
  • An important consideration when designing a smoke control system is to ensure that evacuation is faster than the spread of smoke/fire.
  • Controlling fire size, typically by means of hosepipes, hydrants and sprinklers should be a part of the overall smoke management program.
  • An automatic fire suppression system would be expected to limit the heat release rate and control the spread of fire.
Compartmentation
  • Compartmentation involves use of barriers with sufficient fire endurance to prevent spread of smoke to spaces remote from the fire.
  • The method employs walls, partitions, floors, doors, smoke barriers, smoke dampers, and other fixed and mechanical barriers.
  • The effectiveness of compartmentation is limited by the extent to which the free leakage paths are controlled through the barriers.
  • Smoke control system designers often use the compartmentation method in combination with the pressurization method.
Exhaust ventilation
  • Smoke control in large open areas with high ceilings such as atria, shopping malls, concourse, airports, etc. is best achieved by exhaust ventilation.
  • Hot smoke is collected at the high level in a space, where it is vented outside by means of a powered smoke exhausting fan.
  • Make-up supply air below the smoke layer is also crucial, and is provided from the adjacent spaces free of smoke.
Dilution
  • The dilution method clears smoke from spaces remote from a fire.
  • The method supplies outside air through the HVAC system to dilute smoke.
  • Using this method helps to maintain acceptable gas and particulate concentrations in compartments subject to smoke infiltration from adjacent compartments.
  • In addition, the fire emergency service can employ the dilution method to remove smoke after extinguishing a fire.
  • Smoke dilution is also called smoke purging, smoke removal, or smoke extraction.
  • The approach may be used, for example, to clear smoke that has infiltrated a protected space such as an escape corridor or refuge lobby.
  • Also dilution can be beneficial to the fire service for removing smoke after a fire has been extinguished.
Airflow
  • The airflow method controls smoke in spaces that have barriers with one or more large openings.
  • It is used to manage smoke through open doorways, subway, railroad, and highway tunnels. The method employs air velocity across or between barriers to control smoke movement.
  • A disadvantage of the airflow method is that it supplies increased oxygen to a fire.
  • Within buildings, the airflow method must be used with great caution.
  • The airflow method is best applied after fire suppression or in buildings with restricted fuel.
Pressurization systems
  • The method employs a pressure difference across a barrier to control smoke movement.
  • The pressurization systems are installed mainly in the stairwells, elevator shafts, refuge spaces and other egress routes.
  • The high-pressure side of the barrier is either the refuge area or an exit route.
  • The low-pressure side is exposed to smoke. Airflow from the high-pressure side to the low-pressure side (through construction cracks and gaps around doors) prevents smoke infiltration.
  • A path that channels smoke from the low-pressure side to the outside ensures that gas expansion pressures do not become a problem.
  • A top-vented elevator shaft or a fan-powered exhaust can provide the path. In contrast to exhaust ventilation and dilution systems, the pressurization systems are designed to protect zones away from the fire source.

Important

  • Smoke management systems are designed to modify, dilute, redirect, or otherwise influence the movement of smoke in a building experiencing a fire, but not necessarily to control it or limit its movement.
  • The mechanisms of compartmentation, dilution, airflow, pressurization, and buoyancy are used singly or in combination to manage smoke conditions in fire situations.

2) Smoke Control

  • Smoke control systems are intended to limit and control the movement of smoke during a fire.
  • The most common approach involves using pressure differences on either side of the boundaries of the fire area.
  • The example is stairwell pressurization system.
  • Typically the pressure differentials are created by actively controlling dedicated mechanical fans and dampers (if applicable) to supply the stairwell with 100% outdoor air.

Related video

Leave a Reply

Your email address will not be published. Required fields are marked *

error: Content is protected !!