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The Official Website of Dr. John H. Klote, PE -  Updated June 22, 2015

Smoke is the major killer in building fires, and smoke control

provides significant protection from the threat of smoke.

Scale Model Fire Testing

In today’s world of powerful computers and computational fluid dynamics (CFD), many people do not realize how extensively scale modeling has been used, and scale modeling is still being used. Scale modeling is based on established engineering principles developed over a century ago, and these principles have been verified in a wide range of applications including aircraft design, automobile design, boiler design, fire research and fire protection engineering.

Because scale modeling is done in the physical world, it has a reality that cannot be equaled by any computer simulation. Scale modeling is often used to verify CFD simulations. The following is a brief overview of scale modeling, and Chapter 21 of the Handbook of Smoke Control Engineering has more detailed information.

Froude modeling is the kind of scale modeling that is used for atrium smoke control. The Froude number is a dimensionless number that is the ratio of inertial forces to buoyancy forces. In fires and smoke flow, buoyancy is very important. The validity of Froude modeling has been established over many decades. In Froude modeling, the temperature is taken to be the same in both the model and the full scale facility. In the figure at the right, it can be seen how close temperatures are in the model and in full scale for a corridor smoke flow experiment conducted at NIST. The other parameters (velocity, volumetric flow, mass flow, time, heat release, and pressure difference) in the model are related to those in full scale by scaling equations.

In Froude modeling, a small model of the full size facility is built, and fire tests are conducted in the model. During a test, measurements of some of the parameters are taken, and often video recordings of the tests are made. Scale model testing uses the same kinds of instruments as are used for full scale fire tests. The scaling equations are used to convert the measurements from the scale model tests to data applicable to a full scale facility.

Comparison of Corridor Temperatures Using

Froude Modeling

(Fire tests conducted at NIST.)