





         ESTIMATING THE ENVIRONMENT AND THE RESPONSE OF SPRINKLER LINKS IN
          COMPARTMENT FIRES WITH DRAFT CURTAINS AND FUSIBLE LINK-ACTUATED
                            CEILING VENTS - AN OVERVIEW













                                 Leonard Y. Cooper
                             Center for Fire Research
                           National Bureau of Standards
                            Gaithersburg, MD 20899, USA












                          Tenth Joint Meeting of the UJNR
             (US-Japan Conference on Utilization of Natural Resources)
                         Panel on Fire Research and Safety
                                  Tsukuba, Japan
                                  June 9-10, 1988


         ESTIMATING THE ENVIRONMENT AND THE RESPONSE OF SPRINKLER LINKS IN
          COMPARTMENT FIRES WITH DRAFT CURTAINS AND FUSIBLE LINK-ACTUATED
                            CEILING VENTS - AN OVERVIEW

                                 Leonard Y. Cooper
                             Center for Fire Research
                           National Bureau of Standards
                            Gaithersburg, MD 20899, USA

                                     ABSTRACT

        A physical  basis for  estimating the fire-generated environment and
        the response of sprinkler links in well-ventilated compartment fires
        with  draft  curtains  and  fusible  link-actuated  ceiling vents is
        discussed.   Phenomena taken  into account  include:   growth of the
        smoke layer  in the  curtained compartment; the flow dynamics of the
        buoyant fire plume; the  flow of  smoke through  open ceiling vents;
        the flow  of smoke  below draft  curtains; continuation  of the fire
        plume in the upper layer;  heat transfer to the  ceiling surface and
        the thermal  response of  the ceiling;  the velocity and temperature
        distribution of plume-driven near-ceiling flows and  the response of
        near-ceiling-deployed fusible links.

                                 1.  INTRODUCTION

        Consider a  space defined  by ceiling-mounted  draft curtains with a
        fire and with near-ceiling  fusible-link-actuated ceiling  vents and
        sprinklers.   The curtained area can be considered as one of several
        such spaces in a  large building  compartment.   Also, by specifying
        the curtains  to be deep enough they can be thought of as simulating
        the walls of a single uncurtained compartment.  This paper discusses
        critical physical  phenomena which determine the overall environment
        in the curtained space up to the time  of sprinkler  actuation.  The
        objective  is  to  identify  and  describe the phenomena in a manner
        which captures the essential features of this generic  class of fire
        scenario, and  allows for  a complete  and general,  but concise and
        relatively simple mathematical/computer simulation.

        The overall building compartment is assumed to have  near-floor wall
        vents  which  are  large  enough to maintain the inside environment,
        below any near-ceiling smoke  layers  which  may  form,  at outside-
        ambient conditions.   Figure  1 depicts the generic fire scenario of
        interest.  It is assumed that a two-layer  zone-type model describes
        adequately the  phenomena under  investigation.   The lower layer is
        identical to the outside ambient.   The upper  smoke layer thickness
        and properties  change with  time, but  at any  instant the layer is
        assumed to be uniform  in space.   Conservation  of energy  and mass
        along with  the perfect gas law is applied to the upper layer.  This
        leads to equations  which  require  estimates  of  the  net  rate of
        enthalpy flow  plus heat  transfer and  the net rate of mass flow to
        the upper  layer.    Qualitative  features  of  the  phenomena which
        contribute to these flows and heat transfer are described briefly.


                         2. DESCRIPTIONS OF THE PHENOMENA

        Flow  Through  the  Ceiling  Vents.   Flow is driven through ceiling
        vents  by  cross-vent  hydrostatic   pressure   differences.     The
        traditional   calculation   uses   orifice-type  flow  calculations.
        Bernoulli's equation  is applied  across a  vent, and  it is assumed
        that away  from and  on either  side of  the vent the environment is
        relatively quiescent.   Figure  2 depicts  the known, instantaneous,
        hydrostatic  pressure  distribution  in  the outside environment and
        throughout the thickness of the curtained space.  These are  used to
        calculate the resulting cross-vent pressure difference, and then the
        actual instantaneous mass and enthalpy flow rates through a vent.

        Flow Below the Draft Curtains.  When the layer interface drops below
        the bottom of the draft curtains the smoke starts to flow out of the
        curtained space.  As with  the  ceiling  vents,  this  flow  rate is
        determined by  the cross-vent  hydrostatic pressure  difference.  As
        depicted in Figure 3, however, in this case  the pressure difference
        is  not  constant  across  the  flow.    Nonetheless,  even  in this
        configuration the instantaneous  flow  rates  are  easily determined
        with well-known  vertical-vent flow  equations used traditionally in
        zone-type fire models.

        The Fire, the Fire Plume, and  Radiation Heat  Transfer.   The major
        contributor to the upper layer flow and surface heat transfer is the
        fire and its plume.  This is depicted  in Figure  4.   It is assumed
        that the  rate of  energy release of the fire's combustion zone does
        not  vary  significantly  from  known  free-burn  values  which  are
        available and  assumed to  be specified.  A known, fixed fraction of
        this energy is assumed  to be  radiated isotropically,  like a point
        source, from  the combustion zone.  The smoke layer is assumed to be
        relatively transparent  and  not  participating  in  any significant
        radiation heat transfer exchanges, i.e., all radiation from the fire
        is incident on the bounding surfaces of the compartment.

        A  plume  model  is  selected  from  the  several  available  in the
        literature  and  this  is  used  to  determine  the rate of mass and
        enthalpy flow in the plume at the elevation of the  layer interface.
        It is  assumed that  all of this flow penetrates the layer interface
        and enters the upper layer.

        As the plume flow enters the  upper  layer  the  forces  of buoyancy
        which  act  to  drive  the  plume  toward  the  ceiling  are reduced
        immediately because of the temperature increase  of the  upper layer
        environment  over  that  of  the  lower  ambient.   As a result, the
        continued ascent of the plume gases will be less vigorous,  i.e., at
        reduced velocity,  and of higher temperature than it would have been
        in  the  absence  of   the  layer.     Methods   of  predicting  the
        characteristics  of   the  modified   upper  layer  plume  flow  are
        available.

        Convective Heat Transfer to  the  Ceiling.    Having  penetrated the
        interface, the  plume continues  to rise  toward the  ceiling of the
        curtained compartment.  As it impinges  on the  ceiling surface, the


        plume  flow  turns  and  forms  a  relatively high temperature, high
        velocity, turbulent ceiling jet  which flows  radially outward along
        the  ceiling  and  transfers  heat  to  the  relatively cool ceiling
        surface.  The ceiling jet is  cooled by  convection and  the ceiling
        material  is  heated  in-depth  by  conduction.  Eventually the now-
        cooled ceiling jet reaches  the extremities  of the  curtained space
        and  is  deposited  into  and  mixed  with  the  upper  layer.   The
        convective heat transfer rate and the ceiling surface temperature on
        which it  depends are  both strong  functions of the radial distance
        from the point of plume/ceiling impingement, decreasing rapidly with
        increasing radius.

        Thermal  Response  of  the  Ceiling.    The  thermal response of the
        ceiling is driven  by  transient  heat  conduction.    For  times of
        interest here,  radial gradients  in ceiling  surface conditions are
        small enough so that  the  conduction  heat  transfer  is quasi-one-
        dimensional in  space.    Thus,  the thermal response of the ceiling
        can be obtained  from  the  solution  to  a  set  of one-dimensional
        conduction problems at a few discrete radial positions.  These would
        be solved subject to net convection and radiation heat flux boundary
        conditions.    Interpolation  between  the solutions would lead to a
        sufficiently smooth representation of  the distributions  of ceiling
        surface temperature  and convective  heat transfer rate.  The latter
        of these would be integrated over the ceiling surface to  obtain the
        net instantaneous  rate of  convective heat transfer losses from the
        ceiling jet.

        The Ceiling Jet and  the  Response  of  Fusible  Links.   Convective
        heating  and  thermal  response  of  a  near-ceiling fusible link is
        determined from the  local  ceiling  jet  velocity  and temperature.
        These will  depend on vertical distance below the ceiling and radial
        distance from the fire plume axis.  If and when its fuse temperature
        is  reached,  the  device(s)  being  operated  by  the  link will be
        actuated.

        For radial distances of interest, relatively near to  the plume, the
        ceiling  jet   is  an   inertially-dominated  flow.    Its  velocity
        distribution, depicted  in  Figure  5,  can  be  estimated  from the
        characteristics of  the plume, upstream of ceiling impingement.  The
        ceiling jet temperature distribution, depicted  in  Figure  6  for a
        relatively "hot"  or "cool"  ceiling surface, is then estimated from
        the now-known velocity, upper layer temperature, and ceiling surface
        temperature and heat flux distributions.

                      3.  MODEL EQUATIONS AND A COMPUTER CODE

        A  complete  set  of  model  equations  corresponding  to  the above
        description was developed and presented in [1] with  a complete list
        of references.   This  is the  basis of  a computer model, now under
        development, which will be used to study parametrically a wide range
        of relevant fire scenarios.  It is planned to present results of the
        parametric study in a companion document to [1].


                               4.  ACKNOWLEDGEMENTS

        The author  acknowledges  gratefully  the  AAMA  Research Foundation
        which supported this work.

                                  5.  REFERENCES

        [1].    Cooper, L.Y., Estimating the Environment and the Response of
                Sprinkler Links in Compartment Fires with Draft Curtains and
                Fusible Link-Actuated  Ceiling Vents - Part I: Theory, NBSIR
                88-3474, National Bureau of  Standards, Gaithersburg, April,
                1988.





                               (figure not included)

        Figure 1.  Fire in a building space with draft curtains and ceiling
        vents.

                               (figure not included)

                      Figure 2.  Flow through a ceiling vent.

                               (figure not included)

                      Figure 3.  Flow below a draft curtain.

                               (figure not included)

      Figure 4.  The fire, the fire plume, and heat transfer to the ceiling.

                               (figure not included)

                         Figure 5.  Ceiling jet velocity.

                               (figure not included)

                        Figure 6.  Ceiling jet temperature.