Chapter 18

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 • Very complex subject area with many facets

3. Principles, Advantages,and Effects of Ventilation • Ventilation: relief of products of combustion • Essential to fire suppression • Benefits of ventilation: • Deprives fire of ability to heat up structure • Ventilation 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 • Exerts pressure on anything that surrounds it • Fire spreads by convection and radiation with rising of heated air • Fire can spread by pressure • Structures built today outfitted with heavy insulation and tight weatherproof seams • Many buildings have unopenable windows • Ventilation important in these structures

5. Table 18-1 Gases Produced by Fire

6. Considerations forProper Ventilation • Heat tends to rise, bringing smoke with it • Smoke collects under vertical obstructions • Mushrooms in all directions when it meets obstruction • Gradually fills the structure from highest point • Vertical ventilation: removal of gases and smoke through vertical channels • Horizontal ventilation: channeling of smoke and heat through horizontal openings

7. Figure 18-1 Heat, smoke, and fire will follow the path of least resistance and find their way through any available opening.

8. Figure 18-4 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 as heat and light • Ventilation removes harmful agents • Carbon dioxide accelerates respiration • Increases the rate of toxin absorption • Ventilation prevents: • Flashover and backdraft • Smoke explosion • Rollover/flameover

10. Flashover • As trapped heat accumulates at the ceiling, temperature increases • When temperature reaches ignition point of any substance in the room, new combustion occurs • Forms a chain reaction that causes the entire room and all contents to burn • Very rapid fire spread

11. Backdraft (Smoke Explosion) • Rapid ignition of smoke and unburned products of combustion • Result of introduction of oxygen into environment • With the heat, pressure builds in the confined space • When an opening is made a billow of smoke escapes • Tunnel of fresh air finds its way to the fire • Ignition from seat of the fire burns back to opening along air tunnel

12. Signs of a Potential Backdraft • Short distance to opening • Backdraft unspectacular • Appears as if fire is flaring up • Long distance to opening • Amount of proper concentration from opening to seat is greater • Ignition travels greater distance and amasses greater force • Almost instantaneous reaction like an explosion

13. Rollover/Flameover • Heat brings products of combustion to higher levels • Usually accumulate near the ceiling • Accumulated heat reaches ignition point • Spread across room at ceiling level • Fingers of flame reach across the room, followed by a wall of flame • Advancing hoseline disrupts the upper thermal layer • Disrupts the rollover phenomenon

14. What Needs to be Vented? • Without ventilation, expanding heated steam and smoke will roll over the wall of water • Drop down behind the hose team • Long before entire building requires venting, smaller voids and compartments need to vent • Exhaust increasing pressure and intensifying heat • If done in a timely manner, involvement of entire building might be avoided

15. (A) Figure 18-9 (A) 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. (B) Figure 18-9 (cont’d.) (B) 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 subcompartments • Example: apartments • Each subcompartment can be subdivided • Example: rooms • Each subcompartment can be further subdivided • Example: closets • Building might have eaves, peaks, gables, etc.

18. Cocklofts • Cockloft: space between ceiling of top floor and bottom of roof • 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 • All heat follows the path of least resistance • Unobstructed channel in form of horizontal or vertical void • Heat and fire extend without being seen • Following pipe chases or electrical wire pathways • Ventilating these by opening at highest points exposes extending fire for extinguishment • Trapped heat diffused into unheated spaces • Minimizes risk of heating up a new portion

20. Figure 18-10 Voids in a typical structure that can trap heat and permit fire extension.

21. Figure 18-10 (cont’d.) Voids in a typical structure that can trap heat and permit fire extension. 18.21

22. Air Movement • Convection • Venting carries heat out to atmosphere • Conduction • Venting prevents heat from traveling to uninvolved areas of the structure • Radiation • Venting delays or prevents exposed material from reaching its ignition temperature

23. Types of Ventilation • Several methods used individually or in combination • Natural ventilation: open windows and doors • Mechanical ventilation: use smoke fans and water to create air movement

24. Natural • Opening windows and doors provides natural ventilation • When time not essential; slower venting operation • Appropriate for light smoke condition where incident is under control • Method of choice for residual smoke removal • Cut a hole in the roof or break out windows when greater volumes of smoke need to be removed

25. Figure 18-12 Smoke will be carried throughout the building to upper floors by normal air currents mixed in with the heat.

26. Mechanical • HVAC systems can be used for ventilation in climate-controlled buildings • Smoke fans are placed in opening to suck out smoke and heat • Establish unobstructed path of airflow from outside opposite the fan • Disadvantage: fire crew exposed to smoke and heat • Air introduced via PPV fans or blowers • Hydraulic ventilation: water creates air movement

27. Figure 18-14 A smoke ejector exhaust fan placed in an opening will pull air through the fan as it ejects air out of the structure.

28. Figure 18-16 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.

29. Mechanics of Ventilation • Entire ventilation process is the movement of air from high-pressure location to lower pressure • Natural tendency of air is to move from high pressure to lower pressure • Assists the firefighter in ventilation

30. Vertical Ventilation • Based on the “heat rises” rule of physics • Heat collects at upper levels and spreads fire to those levels • Opening vertical arteries releases pent-up gases • Reduces chance of fire spreading • Heated air replaced with cooler air at lower levels • Improved conditions help crew in locating the fire and searching for victims

31. Horizontal Ventilation • Conforms to same rules of vertical ventilation • Both are a form of diffusion • Molecules spill excess levels of high concentrations into areas of low concentrations • Molecules move laterally as well as vertically • Molecules bounce off walls and move through openings • Openings are made • Smoke and heat are channeled out

32. Figure 18-21 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.

33. Ventilation Techniques • Many techniques used to effect ventilation • Some are simple and require no tools • Others are more complex and dangerous to implement, and require sophisticated tools

34. Break Glass • Quickest way to open a building is to break glass • Best investment of time for results if done properly • Many windows can be broken in time it takes to force one locked door • Glass can penetrate skin deep enough to sever arteries and veins • Wear protective equipment

35. Open Doors • Opening a door will usually exhaust huge volumes of smoke and heat built up • Keeping door on its hinges is a good practice • May need to close the door to limit fire extension

36. Effects of Glass Panes • Many windows have several panes of glass separated by wood or aluminum dividers • Entire window should be removed • Remove sash, cross members, etc. • Remove all glass • Sweep around perimeter with a tool • Remove glass with a tool: two steps • Break through glass from upper to lower sashes • Sweep perimeter to remove remaining glass

37. Rope and a Tool • When operating off a flat roof beyond reach of a ladder • Rope secured to the tool • Turn of rope taken around firefighters hand • Toss tool out as far as possible from building in horizontal direction • This technique leaves shards of glass in place • Does not remove screens, window shades or curtains • Effective when no other approach easily made

38. Hook or Pike Pole • Length of pole keeps firefighter a safe distance from falling glass • Longer hook enables access to out-of-reach windows • Hook can also be used to extend reach of firefighter attempting to open or close a door • Pry tool to remove roof material • Used for other purposes that extend the reach or remove firefighter from dangerous positions

39. (A) (B) Figure 18-23 Making a ventilation hole requires some preplanning. (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.

40. (D) (C) Figure 18-23 (cont’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. 18.40

41. (E) (F) Figure 18-23 (cont’d.) (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 ax to remove window glass, the flat side of the ax head should be used, not the point or the striking surface.

42. Iron or Halligan • Iron or Halligan tool brought down diagonally through the glass • Start at the upper corner • Tool sweeps around the perimeter to clean out any large shards • Short length a disadvantage • Places firefighter near flying glass • Places firefighter in path of heat and smoke • Plan carefully to minimize risk

43. Ax • Ax affords limited reach and places firefighter in hazardous location • Use an ax for venting glass • Side of ax breaks the glass • Do not use blade portion • Use of striking head might cause firefighter to lose grip on the handle • This technique will not break tempered glass • Sharp pointed tool required

44. Portable Ladder • Check for overhead obstructions • Place ladder to side of window against side of house • Measure the base so that the tip will fall into the glass at about 2/3 the height of the window • Reposition the ladder in front of the window • Perpendicular to the ground • Shove the ladder into the building • Tip of ladder crashes through upper pane

45. Negative Pressure Ventilation • Negative pressure created on back side of fan blade • Place a fan in a window facing the outward flow • Heat and smoke trapped in the compartment forced out • Barrier must be created to separate positively charged air from negatively charged air • Effective in limited access compartments • Do not use during the attack

46. (A) (B) Figure 18-24 (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.

47. (C) (D) Figure 18-24 (cont’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. 18.47

48. Positive Pressure Ventilation • Injects air into compartment and pressurizes it • Smoke and heat carried into areas of lower pressure outside the structure • Fans can be set up to augment one another • For every cubic foot of air injected into a compartment, a cubic foot of air must be ejected • Most efficient when exhaust opening is ¾ to 1½ times the size of the entrance opening

49. Figure 18-25 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.

50. Roof Ventilation • Use penthouse doors, skylights, and ventilation shafts for vertical ventilation • Two types of vertical openings: • Offensive • Defensive • Place offensive openings into structure and evaluate need for defensive ventilation • Directly over the fire, if possible • Strip cut (trench cut) is an example of defensive ventilation