system for quantitative color nomenclature that has continued to be used for 70 years. Judd, serving as the U.S. Joint Representative to the CIE, was one of the principal architects of that standard. His paper laid out technical recommendations that were accepted a year later, together with additional data developed by John Guild of the National Physical Laboratory (NPL) in the UK [8].

The system of colorimetry that Judd envisioned in 1930 has been a foundation for technologies not even dreamed of then-color photography (Kodachrome was invented in 1935), color television, modern color printing, and digital imaging. The tools of today's electronic commerce-color scanners, color-calibrated computer monitors, and all manner of color printers— all still rely on the 1931 CIE color system for “device independent" color specifications.

As beautiful as the Gibson and Tyndall work was, it was not without warts. The most famous occurs in the blue-violet portion of the spectrum, where they were forced to choose between conflicting data. They wrote, "The I. E. S. [Illuminating Engineering Society] data in the violet have been accepted by the authors for lack of any good reason for changing them, but the relative as well as absolute values are very uncertain and must be considered as tentative only." Their guess was wrong, but it so quickly earned acceptance that it did not remain "tentative" for very long. Years later, Judd attempted to institute an "improved" version of the visibility curve [9], but the Gibson and Tyndall version had been so thoroughly adopted that the revision never gained wide usage.

The second problem is more subtle and beguiling. The world of Gibson and Tyndall did not include the narrow-band light sources so common today: the phosphors in fluorescent lamps and CRT displays, lasers and LEDs, and the high-efficiency outdoor lighting that turns nighttime into a murky orange. The modern system of physical photometry based upon a simple visibility curve is no longer enough, not because of flaws in the curve, but because the human visual system is much more complex than this simple model suggests. Our vision responds nonlinearly to combinations of narrow-band lights, and perceived brightnesses can differ markedly from the predictions of their model. In a sense, it is the same problem that was recognized in the 1920s as the limitation of equality-of-brightness matching. The data told a story which was not understood then, nor of much technological importance. Today, vision researchers are revisiting the issue in an attempt to improve upon the standard model.

Nonetheless, to the extent that we continue to use electronic instruments to observe our surroundings, and to the extent that physical photometry remains the gold

standard around the world for the metrology of lighting, the Gibson and Tyndall curve continues to play an essential role in estimating our perception of light more than 75 years after its introduction.

Kasson S. Gibson received his education at Cornell and joined NBS in 1916. In addition to the work described here, he made important contributions to the design of optical filters for transforming radiation from incandescent lamps to simulate natural daylight. He headed the work on photometry and colorimetry at NBS from 1933 to his retirement in 1955, publishing over 100 papers in spite of his administrative responsibilities. Gibson served as president of the Optical Society of America from 1939 to 1941 and was a Fellow of the American Physical Society, Illuminating Engineering Society, and American Association for the Advancement of Science. He died in 1979 at the age of 89.

Edward P. T. Tyndall worked at NBS in 1917-1919 and later returned for shorter stays as a visiting researcher. He spent most of his career as Professor of Physics at the University of Iowa, where he did important research on the optical and electrical properties of metals. He distinguished himself as a teacher and supervised 74 masters and doctorate students. He also died in 1979 at age 86.

Prepared by Jonathan E. Hardis.

Bibliography

[1] K. S. Gibson and E. P. T. Tyndall, The Visibility of Radiant Energy, Sci. Pap. Bur. Stand. 19, 131-191 (1923).

[2] Y. Le Grand, Light, Colour and Vision, 2nd ed., translation by R. W. G. Hunt, J. W. T. Walsh, and F. R. W. Hunt, Chapman and Hall Ltd., London (1968).

[3] P. G. Nutting, The Luminous Equivalent of Radiation, Bull. Bur. Stand. 5, 261-308 (1908).

[4] W. W. Coblentz and W. B. Emerson, Relative Sensibility of the

Average Eye to Light of Different Colors and Some Practical Applications to Radiation Problems, Bull. Bur. Stand 14, 167-236 (1918).

[5] P. K. Kaiser, Photopic and Mesopic Photometry: Yesterday, Today and Tomorrow, in Golden Jubilee of Colour in the CIE, The Society of Dyers and Colourists, Bradford, UK (1981).

[6] W. R. Blevin and B. Steiner, Redefinition of the Candela and the Lumen, Metrologia 11, 97-104 (1975).

[7] D. B. Judd, Reduction of Data on Mixture of Color Stimuli, Bur. Stand. J. Res. 4, 515-548 (1930).

[8] W. D. Wright, The Historical and Experimental Background to the 1931 CIE System of Colorimetry, in Golden Jubilee of Colour in the CIE, The Society of Dyers and Colourists, Bradford, UK (1981).

[9] D. B. Judd, Report of U. S. Secretariat Committee on Colorimetry and Artificial Daylight, CIE Proceedings Vol. 1, Part 7, p. 11 (Stockholm, 1951), Central Bureau of the CIE, Paris. See also G. Wyszecki and W. S. Stiles, Color Science: Concepts and Methods, Quantitative Data and Formulae, 2nd ed., John Wiley & Sons, New York (1982) p. 330.

From its earliest years, NBS has had international leadership in the measurements, standards, and technologies associated with prevention of human suffering and losses of lives, property, and societal capabilities to unwanted fires. A major milestone in fire safety engineering, internationally, was publication of Tests of the Severity of Building Fires [1] in 1928. Its author was Simon H. Ingberg, Chief, Fire Resistance Section, U.S. Bureau of Standards.

Fire statistics published by the National Fire Protection Association [2] show that about two million fires are reported in the United States each year, causing 4000 deaths and 8 billion dollars in property damage. This is bad, but it used to be worse. Early in the 20th century, with a much smaller U.S. population, twice as many people died each year. At that time the fire death rate per 100,000 population was 9.1, in contrast to 1.6 today [2]. The buildings that burned in the early 1900s often collapsed as fire spread throughout the structure. Fire measurement at NBS quantified the intensity and duration of building fires. Simon Ingberg related the measured fire temperatures and duration to equivalent exposure to the standard furnace fire time-temperature curve [3]. Today's fire resistant construction is evaluated using the ASTM E119 standard fire exposure based on the same approach. Ingberg's work provided vital information about the relationship between fire severity as measured in full-scale room and building fire tests and endurance ratings in the standard test method. This provided the guidance for building codes requirements and design approaches for fire resistive construction to contain fire spread in buildings. Today, as a result of confinement, detection, and suppression fire protection strategies, most fires in buildings never grow beyond the room in which the fire started.

In Ingberg's own words:

"One of the main objects of public regulation of building construction is to prevent undue hazard to life and neighboring property from fire. Fire exposure to buildings and building members arises from interior and exterior origins. The evaluation of the exterior exposure can be done with difficulty in quantitative terms, and the gradual accumulation of data from actual fires will probably continue as the main guidance in providing the proper protection. The present paper will deal mainly with methods of gauging the severity of fires resulting from

the burning out of contents of buildings whose wall, floor, and column constructions are fire resistive to such an extent as to be capable of withstanding a complete burning out of building contents without collapse of major details. It is only when the problem is so confined that there is much possibility of obtaining experimentally quantitative information pertinent to the answer sought. The severity of fires completely consuming the combustibles of frame buildings and masonry-walled buildings with combustible interior construction is of interest mainly as it concerns the exposure to adjacent or neighboring buildings and the fire exposure on party and fire walls and on record containers. As it concerns the severity of fires in buildings with interior combustible construction protected with incombustible floor, ceiling and wall finishes, the present discussion will apply up to the limit set by the fire resistance of such protection.

Indications of the intensity of building fires have been obtained from fused metals and from general fire effects on materials on which information is extant as to their reaction to temperature or fire exposure such as in test fires. The fire ruins or reports of fires give, however, little information of the duration of the temperatures in any given portion of the building. The absence of data to enable constructions or devices giving a certain performance in the standard fire test to be applied as protection against fire conditions in buildings with as much precision as results of strength tests are applied for load carrying purposes, led me to consider the possibility of conducting burningout tests in suitably designed structures to obtain the needed information. If such tests could be made to yield quantitative information on the equivalent fire duration to be expected with given building types and occupancies, it would help measurably to place the whole structure of fire resistance requirements on a rational basis. Fire is a contingent condition that may or may not involve a building or given portion thereof in its lifetime. In theory, at least, the owner should be required to make provision for safety to life within and near the building, and for protection to adjacent and neighboring property only as it concerns the building type and size proposed and the occupancy it is intended to house. With require

such as the use of non-combustible metal furnishings instead of wooden furnishings, to examine the change in fire intensity. Building ventilation was provided to maximize fire conditions by adjusting openings in windows (Fig. 3). Temperatures were measured at 35 to 40 points in the smaller building and 100 in the larger.

Results of ten large-scale tests were analyzed and tabulated to relate the combustible content (in terms of either mass or calorific energy per unit area) to the equivalent fire duration (in hours and minutes) of a standard fire furnace test exposure temperature curve. Except for the fact that average room temperatures in the fire tests generally increased after ignition, then decreased from a peak as fuel was depleted, the two curves were not identical in shape. So the challenge for Ingberg was to adopt a method for gauging the overall severity of a fire test relative to the standard fire exposure. He proposed that the area under the time-temperature curve, but above selected base-line temperatures, represented an approximate gauge of exposure severity. He recognized that this is an approximation, but that no better measure of comparison could be conveniently applied. This remains true today.

Ingberg's tests related severity of fires resulting from a total combustible content (including finished floors and trim) in offices and record rooms ranging from 49 kg/m2 to 290 kg/m2 to be the equivalent to standard furnace fire exposures of 1 h to 7.5 h, respectively.

As a result of Ingberg's work, it became possible to develop fire codes and design approaches that related the combustible load in a room, based on its contents and use, to the performance of fire-resistant construction details in the standard fire test.

NBS under Ingberg's leadership continued to explore fire severity, including notable full scale tests in buildings near the corner of 10th and B streets, NW, in downtown Washington, DC, scheduled for demolition to obtain space to construct today's Justice Department Building on the Federal Triangle (Fig. 4). In 1928, this full-scale fire test of buildings ignited, then allowed to burn without application of water, was unique in the history of fire protection engineering. In the test conducted on Sunday morning, June 17, 1928, fire conditions in adjacent five-story and two-story brick openjoist construction buildings were measured for the purpose of comparison to the standard furnace exposure conditions and duration. In addition, the test gathered data about fire exposures to support test standards for fire resistant safes and other record containers.

It remained necessary to provide uniform fire-resistance classifications for building constructions as a sound basis for permitting the use of new systems of construction that could be demonstrated to be comparable in performance to systems prescribed by building codes. A Subcommittee on Fire-Resistance Classifications was organized under the auspices of the U.S.