Leonard Y. Cooper

The interaction of an isolated sprinkler spray and a two-layer compartment fire environment

Abstract A model is developed to simulate the interaction of a sprinkler and a two-layer fire environment under arbitrary conditions of sprinkler elevation, upper-and lower-layer thickness, and temperature. The sprinkler is characterized by a water flow rate and four measurable device parameters. The model simulates the effects of the sprinkler spray as it entrains, drives downward, humidifies, and cools gases in the upper and lower layers. It predicts the flow rates of mass, enthalpy, products of combustion and evaporated water to each of the two layers as a result of sprinkler operation. Results of example calculations are presented.

Negatively buotant wall flows generated in enclosure fires

Abstract This paper considers wall flows that arise in enclosure fires. Such flows are generated due to the temperature difference between the wall and the adjacent environment as well as due to the downward turning of the fire-plume-driven ceiling jet at the corners of the compartment. At various stages of fire growth and at several locations, the flow is subjected to an opposing buoyancy force. These flows are termed negatively buoyant and the paper investigates in detail the penetration and heat transfer characteristics of flows relevant to enclosure fires. The transport of mass, momentum and energy in wall flows is determined quantitatively, using available analytical results on boundary layer flows. The significance of wall flow effects in a typical compartment fire is studied. It is shown that these effects are important, since they cause additional transport which is comparable to that due to the fire plume or the flow at the opening, and must be included in a mathematical model for an accurate prediction of the changing environment in the enclosure. Negatively buoyant wall and free jets are studied experimentally to obtain the penetration depth, the entrainment into the flow and the wall heat transfer. The penetration of buoyancy-induced wall flows and of negatively buoyant wall jets in a two-layer stably stratified environment is also studied in detail experimentally. The experimental results are presented in the form of correlating equations which can be applied to the existing models for compartment fires. An analytical, integral model for including wall flows is presented, followed by a more accurate treatment based on the experimental results obtained. It is shown that the inclusion of wall flows is important in an accurate prediction of the downward movement of the interface, between the upper and lower zones of a room fire, at the initial stages of the fire and also in the calculation of the transport processes at later stages. Thus, the paper presents the basic information needed for the incorporation of wall flow effects into existing mathematical models for room fires and applies the results to a few typical fires. The trends observed are physically reasonable and agree with earlier work on this problem.

A concept for estimating available safe egress time in fires

Available Safe Egress Time (ASET) in enclosure fires is defined as the time between fire detection and the onset of conditions which are hazardous to continued human occupancy. A general technique for estimating this time interval is introduced. A description of hazard development is presented. This description identifies the variables of fire growth which are significant to life safety. A conceptual engineering model which simulates these variables is formulated. Because of the primary focus on life safety, as compared with property protection or structural integrity per se, the suggested modeling includes significant simplifying assumptions which would not be otherwise justified. The concepts developed in this paper provide a rational basis for the use of a mathematical model and user oriented computer program, presented in other works, to actually carry out ASET calculations for compartments of fire origin.

Estimating the environment and the response of sprinkler links in compartment fires with draft curtains and fusible link-actuated ceiling vents—Theory

Abstract The physical basis and associated mathematical model 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 developed. Complete equations and assumptions are presented. Phenomena taken into account include: the flow dynamics of the upward-driven, buoyant fire plume; growth of the elevated-temperature smoke layer in the curtained compartment; the flow of smoke from the layer to the outside through open ceiling vents; the flow of smoke below curtain partitions to building spaces adjacent to the curtained space of fire origin; continuation of the fire plume in the upper layer; heat transfer to the ceiling surface and the thermal response of the ceiling as a function of radial distance from the point of plume-ceiling impingement; the velocity and temperature distribution of plume-driven near-ceiling flows and the response of near-ceiling-deployed fusible links as functions of distance below the ceiling and distance from plume-ceiling impingement. The theory presented here is the basis of a user-friendly computer program, LAVENT, which is supported by a user guide and which can be used to study parametrically a wide range of relevant fire scenarios.

Ceiling Jet-Driven Wall Flows in Compartment Fires

Abstract Analytic estimates are developed for depth of penetration and lateral entrainment of negatively buoyant, ceiling jet-driven wall flows during early times of compartment fire scenarios. When walls are not too far from the fire source of the order of the fire-to-ceiling distance, it is found that the penetration of these downward wall flows is a large fraction of the fire-to-ceiling distance, and that this Traction is relatively independent of the details of fire size and fire-to-wall spacing. Also, net rate of entrainment into the wall flow as it is buoyed back upward to the ceiling elevation is found to be several times larger than the Row rate of the driving ceiling jet flow immediately upstream of wall impingement. Data from five studies reported in the literature are reviewed relative to the analytic results obtained. One of these involved a field model simulation of the flow generated by a buoyant source in an enclosure. Two experimental laboratory studies involved fires in enclosures with ch...

ASET-A computer program for calculating available safe egress time

In the event of a fire in a building compartment the time available for occupants to safely evacuate the compartment, the Available Safe Egress Time (ASET), depends on the time of fire detection and on the time of the onset of hazardous conditions. In order to estimate these two times a dynamic simulation of the developing fire environment in the compartment is required. Also required are specific criteria for the simulation of detection and onset of hazard. A user-oriented computer program which carries out the required simulations and provides estimates for the ASET has been developed. This paper describes the program and its use. For fire growth in a particular fuel assembly, a single program run can be used to evaluate the ASET from enclosures (which are assumed to contain the fuel assembly) of different heights and areas, and under a variety of different detection and hazard criteria. The program can be used in either an interactive or batch mode. It is written in ANSI FORTRAN and requires no computer specific subroutines.

The interaction of an isolated sprinkler spray and a two-layer compartment fire environment. phenomena and model simulations

Abstract A general description of the interaction of sprinklers and compartment-fire-generated smoke layers is presented. Various possible aspects of the interaction phenomena (upper-layer smoke entrainment into the sprinkler spray, momentum and mass exchange between droplets and entrained gas, gas cooling by evaporation, buoyancy effects, and others) are discussed in the context of a two-layer-type description of the fire environment. The inputs and outputs for a mathematical submodel which simulates the phenomena are discussed. The submodel is suitable for general use in any two-layer, zone-type compartment fire model. Results from exercising the submodel are presented. These example calculations simulate the interaction between the spray of a real sprinkler device and a range of two-layer fire environments. The calculations reveal an important generic interaction phenomenon, namely, an abrupt and large change in the growth rate of the upper layer that would accompany an increase in upper-layer thickness beyond a critical thickness (for a given upper-layer temperature) or an increase in upper-layer temperature beyond a critical temperature (for a given upper-layer thickness). Exceeding these critical values would lead to a very large rate of growth of upper layer thickness, a growth that could lead to rapid and complete smoke filling of even the largest compartments of fire origin.

Smoke movement in rooms of fire involvement and adjacent spaces

Abstract The key to the solution of fire safety design problems is the capability to predict the dynamics of enclosure fire environments. This paper presents a detailed qualitative description of the generic phenomena which occur during typical fire scenarios. The focus of attention is on effects within building compartments of fire involvement, i.e., compartments made up of a single enclosed space or a space of two or more rooms interconnected by significant penetrations such as open doors or windows. Throughout the discussion reference is made to quantitative methods for predicting some of the most significant of these effects. Reference is also made to available mathematical/computer models which use these latter methods to quantitatively predict the overall fire environment. The basic topics that are covered are: fire growth in combustibles of fire origin; development of the fire plume and interaction of the plume with the ceiling surface; generation of ceiling jet flows which lead to actuation of detection/intervention hardware; interaction of ceiling jets and wall surfaces; growth of the smoke layer; development of wall flows which can be instrumental in drawing smoke down from the upper smoke layer into the relatively uncontaminated, shrinking lower ambient environment; downward radiation from the high temperature smoke layer and upper enclosure surfaces which can ultimately lead to flashover; and onset of conditions which are untenable for human occupancy or property survivability. Topics related to fire-generated environments in multiroom fire/smoke compartments include: dynamics of the smoke and fresh air exchange between the room of fire involvement and the adjacent spaces; dynamics of door/window plumes, ceiling jets, smoke filling and wall flows within adjacent spaces; actuation of adjacent space fire detection/ intervention hardware; and onset of adjacent space untenability. The paper concludes with a brief discussion on the relationship between fire compartment smoke dynamics and smoke movement throughout the rest of a building.

Comparisons of NBS/Harvard VI simulations and data from all runs of a full-scale multi-room fire test program

The NBS/Harvard VI multi-room fire model computer code was used to simulate results of previously reported full-scale, multi-room fire experiments. The tests and simulations involved four different compartment configurations made up of two or three rooms connected by open doorways, four different fire types generated by a methane burner located in the room identified as the burn room, and up to four different doorway openings between the burn room and the adjacent space. A total of nineteen different tests were carried out and simulated. Comparisons between simulated and measured parameters of the fire-generated environments are reviewed. While the computer code is generally found to provide favorable simulations for the entire range of tests, several areas in modeling detail are identified as requiring clarification, research and further improvement. The improvements should be incorporated in future versions of the NBS/Harvard multi-room fire model.

Simulating smoke movement through long vertical shafts in zone-type compartment fire models

A limitation of traditional zone-type compartment fire modeling is the inadequacy of two-layer quasi-steady-buoyant-plume analyses to simulate the fire-generated environment in room configurations with large height-to-span ratios, e.g., elevator shafts and ventilation shafts. Model equations to remove this limitation are developed. These simulate time-dependent flow in a long, ventilated, vertical shaft with an arbitrary vertical density distribution, including one or more intervals along the shaft length where the vertical distribution of the averaged cross-section density may be unstably stratified, i.e., density increasing with increasing elevation. The model equations are partially verified by favorable comparisons between solutions and previously published data from unsteady experiments in long vertical tubes involving initially unstable configurations: saltwater over freshwater and heavy gas over light gas.