Enclosure Fire Dynamics Chapter 1: Introduction Chapter 2: Qualitative description of enclosure fires Chapter 3: Energy release rates, Design fires Chapter 4: Plumes and flames Chapter 5: Pressure and vent flows Chapter 6: Gas temperatures (Chapter 7: Heat transfer) Chapter 8: Smoke filling (Chapter 9: Products of combustion) Chapter 10: Computer modeling Each course unit represents breaking down the problem into individual pieces

Overview General on smoke control in buildings Examples of applications Derivation of conservation equations Smoke filling in small room with small opening: Zukoski method Smoke filling in large room with large opening: Steady-state method Natural ventilation Mechanical ventilation Pressurization of lower layer EFD simply provides a bunch of equations. This lecture will go into detail at the beginning on what we are trying to do with smoke filling. It’s fine to calculate smoke filling, but you also need to know how to do something about it.

How do people die in fires? MGM Grand Hotel Many fire deaths far away from fire

Reasons for smoke control Life safety – maintain the escape path as long as possible Firefighter safety – improve visibility Firefighter operations – reduce time to put out fire Property protection – reduce smoke damage Property protection – reduce temperature and external radiation to fuel packages Continuity of operations = Open for business sooner

Smoke management – preventing smoke spread Smoke control Use of mechanical fans for pressurization Smoke and heat venting Natural (link operated vents) Mechanical

Locations for smoke control Atria Warehouses (rack storage) High rise buildings (stairwells) Shopping malls Performance based designs Increase travel distance Substitute for rated construction (smoke barriers) Elevators for egress

Example: Atria Atrium – singular (one) Atria – plural (many) Opening through floors

Example: Atrium

Example: Preventing smoke spread

Example: Smoke management-pressure Compartmentation with pressurization We can calculate required pressure difference

Example: Single injection point Fail with door open near injection point Limit to 8 stories (Klote and Milke)

Example: Multiple injection points More injection points limits local loss of pressure Determining the design number of open doors can be difficult Is it better to remove smoke high or low in the stairway?

Example: Smoke control by air flow Airflow without barriers can control smoke if the air velocity is sufficient Not usually a recommended method (expensive) Airflow can enhance burning rate

Example: Mechanical exhaust from a large volume space

Example: Balcony spill plume In many cases, the mass flow rate is larger than from an axi-symmetric plume

Example: Roof vents

Example: Natural smoke venting Reduced flow due to obstructions, wind and sprinklers Makeup (replacement) air required

Example: Venting of fire gases

Activation of smoke control system Smoke detector Thermal detector Smoke density detector Specified optical density/obscuration Beam detectors Avoid manual activation, but provide manual activation for fire department

Overview General on smoke control in buildings Examples of applications Derivation of conservation equations Smoke filling in small room with small opening: Zukoski method Smoke filling in large room with large opening: Steady-state method Natural ventilation Mechanical ventilation Pressurization of lower layer EFD simply provides a bunch of equations. This lecture will go into detail at the beginning on what we are trying to do with smoke filling. It’s fine to calculate smoke filling, but you also need to know how to do something about it.

Conservation equations Conservation of mass (C of M) Conservation of energy (C of E) Conservation of momentum Conservation of species (O2, CO2, H2O, soot, fuel)

Compartment Fire Environment

Finite Control Volume

Infinitesimal Control Volume All four give the same result, but just in a different form

Control volume could be one of two layers Hand calculations Two-zone computer models

Or the control volume could be one small piece of the overall enclosure Computational Fluid Dynamics or CFD models

Control surface Surface defining a control volume Mass, energy etc. pass through the control surface

Overview General on smoke control in buildings Examples of applications Derivation of conservation equations Smoke filling in small room with small opening: Zukoski method Smoke filling in large room with large opening: Steady-state method Natural ventilation Mechanical ventilation Pressurization of lower layer EFD simply provides a bunch of equations. This lecture will go into detail at the beginning on what we are trying to do with smoke filling. It’s fine to calculate smoke filling, but you also need to know how to do something about it.

Smoke filling in a room with a small opening (vent) Conservation of mass CV is lower layer Plume is ignored or could be included in upper layer Mass leaves CV through plume and vent (positive)

Smoke filling in a room with a small opening (vent) Remember the Zukoski plume equation Use the energy equation to find Substitute and into C of M equation

Smoke filling in a room with a small opening (vent) A numerical/graphical solution is possible Generalize results by using dimensionless numbers

Non-dimensional smoke filling equation Dimensionless height: Dimensionless HRR: Dimensionless time: Dimensionless form of smoke filling equation

Result of numerical solution by Zukoski (ceiling and floor leaks)

Limitations of Zukoski model Small room and small opening Zukoski plume equation Valid for weak sources No heat loss No pressure change with time Uniform pressure throughout room Expect approximate results only

Overview General on smoke control in buildings Examples of applications Derivation of conservation equations Smoke filling in small room with small opening: Zukoski method Smoke filling in large room with large opening: Steady-state method Natural ventilation Mechanical ventilation Pressurization of lower layer EFD simply provides a bunch of equations. This lecture will go into detail at the beginning on what we are trying to do with smoke filling. It’s fine to calculate smoke filling, but you also need to know how to do something about it.

Steady state smoke control Spaces are typically large (tall) Openings are large, so there is little (no) pressure buildup inside enclosure Flow rates through vents are a function of hydrostatic pressure differences Pressure difference varies over height of opening Two direction vent flow More directions possible with smoke filling in second compartment C of M and C of E equations coupled Must solve at the same time

Steady state smoke control Now do something to stop the upper layer from descending (moving) Rate of smoke venting (exhaust) equals rate of smoke production (entrainment in plume) Steady state Conditions no longer changing with time Method of Tanaka and Yamana

Steady state smoke control Mass conservation for upper layer Conservation of energy for upper layer Heat loss to walls now important

Steady state smoke control We already solved this energy equation in Chapter 6 But now we know z’, so we know the area of the wall being heated, Aw Semi-infinite solid with Tg=Ts

Look at three cases for removing smoke Natural ventilation Mechanical ventilation Pressurization of lower layer

Steady state smoke control natural ventilation from upper layer Mass and energy equations are coupled Should solve both at same time Pressure difference at top of layer moves smoke Thicker layer = greater mass flow Look at solution by trial and error

Steady state smoke control natural ventilation from upper layer Trial and error solution Guess a layer height Solve mass and energy balances Correct layer height guess and density Resolve mass and energy balance

Steady state smoke control mechanical ventilation from upper layer A fan is now placed at the top of the compartment to remove smoke Generally know the fan exhaust rate [m3/s]

Steady state smoke control mechanical ventilation from upper layer

Steady state smoke control pressurization of lower layer A few cautions about pressurization of the lower layer by mechanical ventilation

Full scale test results

Some final cautions There is not universal agreement by fire researchers on these equations Some, but not much, full scale testing Fire model results versus correlations Sometimes easier to just use a fire model Some models have been validated (tested) under smoke control conditions

Any questions?