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Chapter 18

Chapter 18 . Ventilation. Introduction. Ventilation: planned, methodical, systematic removal of pressure, heat, smoke, gases, and flame Essential part of tactical and strategic objectives Late application of proper ventilation subjects firefighters to extreme circumstances.

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Chapter 18

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  1. Chapter 18 Ventilation

  2. Introduction • Ventilation: planned, methodical, systematic removal of pressure, heat, smoke, gases, and flame • Essential part of tactical and strategic objectives • Late application of proper ventilation subjects firefighters to extreme circumstances. • Complex subject area with many facets

  3. Principles, Advantages, and Effects of Ventilation • Ventilation • Essential to fire suppression • Benefits: • Deprives fire of ability to heat up structure • Channels smoke out of the structure • Removal of smoke, heat, and toxic gases add survival time to a potential victim

  4. Heat, Smoke, and Toxic Gases • When fire burns, air heats, expands, and rises. • Convection • Radiation • Structures built today • Heavy insulation • Tight weatherproof seams • Windows that do not open

  5. Gases Produced by Fire

  6. Considerations for Proper Ventilation • Heat tends to rise. • Smoke collects under vertical obstructions. • Mushrooms • Fills the structure from highest point • Vertical ventilation • Horizontal ventilation

  7. Heat, smoke, and fire will follow the path of least resistance and find their way through any available opening.

  8. Air movement is created by water application. Openings in back of the nozzle team will create airflow from behind in the direction of the hose team. It can be a source of fresh cool air, or it can pull fire to the nozzle from behind. Indiscriminate ventilation can be a liability. Careful assessment and proper timing are important.

  9. Fire and Its By-Products • During combustion, energy is released from exothermic reaction: • Heat • Light • Harmful agents • Carbon dioxide • Ventilation prevents: • Flashover and backdraft • Smoke explosion • Rollover/flameover

  10. Flashover • Temperature increases • When temperature reaches ignition point of any substance in the room, new combustion occurs. • Chain reaction • Very rapid fire spread

  11. Backdraft (Smoke Explosion) • Rapid ignition of smoke and unburned products of combustion • With heat, pressure builds • Smoke escapes • Introduction of fresh air • Ignition

  12. Signs of a Potential Backdraft • Short distance to opening • Unspectacular • Flaring up • Long distance to opening • Proper concentration from opening to seat is greater • Greater force • Instantaneous reaction

  13. Rollover/Flameover • Heat brings products of combustion to higher levels. • Accumulated heat reaches ignition point. • Flame reaches across the room, followed by a wall of flame. • Advancing hoseline disrupts the upper thermal layer.

  14. What Needs to be Vented? • Without ventilation • Expanding heated steam and smoke will roll over the wall of water. • Before building requires venting, voids and compartments need to vent. • If timely, involvement of building might be avoided.

  15. Applying water to the upper levels of a thermal layer will cool and disrupt the rollover effect that is apt to occur with the proper conditions. Ventilation is critical when this is done.

  16. As a hose team advances into the fire and sprays water in droplet form, it creates a wall of water and disrupts the high-heat thermal layer and cools the upper levels of the compartment. Water absorbs heat as it turns to steam, expanding 1,700 times as it does. If there is no path for the expanding water/steam conversion, it will take the path of least resistance, in this case over the wall of water and the nozzle team. The water movement will then pull any heat from the back of the nozzle team and roll over on top of it. 18.16

  17. Voids and Compartments • All compartments treated with same understanding • Residential building is a large compartment with many sub-compartments. • Each sub-compartment can be subdivided. • Each sub-compartment can be further subdivided. • Eaves, peaks, gables, etc.

  18. Cocklofts • Major attack point for ventilation crew • Especially in a top-floor fire or fire that has extended into that space

  19. Horizontal and Vertical Voids • Heat follows the path of least resistance. • Unobstructed channel in form of horizontal or vertical void • Heat and fire extend without being seen. • Ventilating horizontal and vertical voids

  20. Voids in a typical structure that can trap heat and permit fire extension.

  21. Voids in a typical structure that can trap heat and permit fire extension. 18.21

  22. Air Movement • Convection • Conduction • Radiation

  23. Types of Ventilation • Methods used individually or in combination • Natural ventilation • Mechanical ventilation

  24. Smoke will be carried throughout the building to upper floors by normal air currents mixed in with the heat.

  25. A smoke ejector exhaust fan placed in an opening will pull air through the fan as it ejects air out of the structure.

  26. Positive pressure literally pressurizes the structure and forces smoke out any path of least resistance. Almost the same effect would occur if a light breeze were blowing directly into the structure from one side and venting out the other side.

  27. Mechanical Ventilation • PPV can be used in a positive pressure attack (PPA) mode; the incident commander must avoid PPV use during the following conditions: • Imminent or confirmed rescue of a firefighter or civilian • Working fire attack • Unknown location of fire • Inability to provide a proper exhaust point • Structure that presents an over-pressurization or hostile event indicator

  28. Mechanics of Ventilation • Ventilation process • Natural tendency of air

  29. Vertical Ventilation • “Heat rises” rule of physics • Collects at upper levels and spreads fire to those levels • Opening vertical arteries • Heated air replaced with cooler air

  30. Horizontal Ventilation • Same rules of vertical ventilation • Both are a form of diffusion • Openings are made • Smoke and heat are channeled out

  31. Heated air has more agitation in its molecules, causing internal pressure in a compartment. This will, in turn, create greater velocity when air exits an opening. Normal diffusion takes much longer to occur when only natural air movement and currents are employed.

  32. Ventilation Techniques • Many techniques used to effect ventilation • Simple and no tools • Complex and dangerous, require sophisticated tools

  33. Break Glass • Quickest way to ventilate • Best investment of time • Time savings • Glass dangers • Wear protective equipment

  34. Open Doors • Opening a door exhausts huge volumes of smoke and heat built up. • Keeping door on its hinges is a good practice.

  35. Effects of Glass Panes • Many windows have several panes of glass. • Separated by wood or aluminum dividers • Remove all glass. • Remove glass with a tool. • Break through glass from upper to lower sashes. • Sweep perimeter to remove remaining glass.

  36. Rope and a Tool • When operating off a flat roof • Rope secured to the tool • Turn of rope around firefighter’s hand • Toss tool out in horizontal direction. • This technique leaves shards of glass.

  37. Hook or Pike Pole • Length keeps firefighter safe • Enables access to out-of-reach windows • Hook also used to extend reach of firefighter attempting to open or close a door

  38. Making a ventilation hole requires some preplanning. (A) (B) (A) Firefighters should make the hole so that heat, smoke, and possibly flame do not envelop them. (B) When working off a ladder, the same general precautions are necessary. Firefighters must be secured to the ladder before performing any action.

  39. Making a ventilation hole requires some preplanning. (C) (D) (C) When venting from above, firefighters use the wind to their advantage and stand off to one side so that they are not standing in the path of any initial billow of heat. (D) When pulling off roof boards, firefighters should work in the clear air with the wind blowing smoke away, and be careful with roof debris. It will most likely be hidden in the smoke. 18.39

  40. Making a ventilation hole requires some preplanning. (E) (F) (E) When removing a skylight, firefighters work with the wind at their backs. It is sometimes less work to lift off the entire housing than to break out each individual pane of glass. (F) When using an axe to remove window glass, the flat side of the axe head should be used, not the point or the striking surface.

  41. Iron or Halligan • Tool brought down diagonally through the glass • Sweep around the perimeter • Short length a disadvantage • Plan carefully to minimize risk

  42. Axe • Affords limited reach • Places firefighter in hazardous location • Use an axe for venting glass • Do not use blade portion • Will not break tempered glass

  43. Portable Ladder • Overhead obstructions • Side of window • Measure the base so that the tip will fall into the glass at about 2/3 the height of the window. • Reposition the ladder. • Shove the ladder into the building.

  44. Negative Pressure Ventilation • Created on back side of fan blade • Place a fan facing the outward flow. • Heat and smoke • Positively charged air and negatively charged air • Limited access compartments

  45. (A) (B) (A) When using an exhaust fan, it is important to cover the openings around the unit. (B) When covering any opening around the exhaust fan, the vacuum necessary to operate efficiently will be created and the exhausted air will not be sucked back around the fan.

  46. (C) (D) (C) When using an exhaust fan in a door, the air will circulate from the exhaust side into the intake side if no provision is made to block that flow. (D) Through the use of plastic, tarps, or even a piece of plywood, the air is prevented from being pulled back into the intake side of the fan. 18.46

  47. Positive Pressure Ventilation • Injects air into compartment and pressurizes • Smoke and heat carried outside the structure • Fans set up to augment one another • For every cubic foot of air injected into a compartment, a cubic foot of air must be ejected. • Exhaust opening size

  48. With positive pressure ventilation, the theory is to actually pressurize the compartment and then the smoke and heat will actually be pushed out another opening. To be effective, certain actions must be taken. (1) The blower or fan must be placed a short distance from the opening so that a “cone of air” is created that just barely exceeds the opening being used. (2) The exhaust opening should be smaller than the introduction opening for maximum efficiency. That opening size depends on the number of blowers and their capacity. There are many variations where this practice can be effective.

  49. Roof Ventilation • Use penthouse doors, skylights, and ventilation shafts • Two types of vertical openings • Place offensive openings into structure • Evaluate need for defensive ventilation • Strip cut (trench cut)

  50. Expandable Cut • Efficient for time expended • Large a hole as needed • Plan the cut • Prevent damage to support rafters or cross members • One large opening produces more airflow than several smaller holes.

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