|Ten Years of Heat Release Research
with the Cone Calorimeter
|by Dr. Vytenis Babrauskas, Fire Science and Technology Inc.
[An updated version of a paper originally published
as: Babrauskas, V., Ten Years of Heat Release Research with the Cone
Calorimeter, pp. III-1 to III-8 in Heat Release and Fire Hazard, Vol. I,
Y. Hasemi, ed., Building Research Institute, Tsukuba, Japan
|ISO 5660 standard was only published in final form
in 1993. However, the Cone Calorimeter was first announced in 1982. Thus, heat
release rate (HRR) research work using the Cone Calorimeter started at that
time, even though certain features, e.g., the smoke photometer, were not
developed until a few years afterwards. In this paper a review is made of what
has been learned so far and where strong research successes have been obtained.
A number of applications where Cone Calorimeter data are already being used are
cited. In addition, some indications are given of where Cone Calorimeter
research and application activities are likely to progress in future
|A brief history of the Cone
|During the late 1970s and early 1980s the importance of a
reliable bench-scale engineering tool for measuring heat release rate was being
realized. A number of such devices had already been built, both at NIST (then,
NBS) and at other institutions. None was felt to be appropriate for normal
engineering laboratory use. The problems were two-fold: errors of measurement,
and difficulty of operation. Insulated box (sensible enthalpy) types of designs
were demonstrated to show large systematic errors. Instruments built on other
measurement principles, such as substitution burner, were capable of good
accuracy but were very complex and difficult to install and maintain. This
indicated that an instrument of a new design was needed. At the same time, the
oxygen consumption principle  was beginning to be known. It shortly became
evident that the successful bench-scale HRR apparatus would be based on using
this measurement principle. Several years of exploratory research on various
instrument designs were conducted. The successful design was termed the Cone
Calorimeter and was first described in an NBS report in 1982 .
The basic principle of the Cone Calorimeter has been unchanged
to this day. Numerous improvements and additions were made, however, to the
point that a current-day apparatus contains few parts identical to the ones on
the apparatus of 1982. The most major change was the introduction of systems for
measuring smoke optically and soot yield gravimetrically; these were described
in 1987 . Most of the other changes involved not changes in function but,
rather, parts redesigned for ease of use or reliability of operation.
The design of the Cone Calorimeter, as finalized, was
considered a pivotal engineering invention-it was awarded the "R&D 100
Award" in 1988. It was the first-ever fire testing apparatus to be recognized by
the award to NIST of the most prestigious American award for technology
The first Cone Calorimeter built outside NIST was constructed
at BRI in Japan in 1985, followed by one at the University of Gent in 1986;
later in that same year 3 commercial units were built and sold in the United
States. Fig. 1 shows the growth of Cone Calorimeters subsequently. Nearly 100
units have now been established, including some which are not charted on Fig. 1
since details are not available of when they were commissioned into service.
Close to 20 countries possess at least one Cone Calorimeter by now.
There is currently one active manufacturer of Cone Calorimeters: Fire
Testing Technology Ltd. In the past, Atlas Electric, Dark Star Research,
University of Ghent, and PL Thermal Sciences produced some units.
Figure 1 The increasing number of Cone
Calorimeters placed into service
The breakdown of ownership at this point stands as
indicated in Table 1. As one might expect, manufacturers' laboratories and
government research laboratories are the most common establishments possessing
Cone Calorimeters. Universities as yet comprise a small fraction, but there is
growing interest in that sector. For-fee testing activities take place at both
the independent laboratories and, in many countries, at government
research/testing laboratories; together these account for nearly 1/4 of the
|Research studies with the Cone
|Subsequent to its standardization, instrumentation developments on the Cone
Calorimeter have focused on some advanced research needs. These included
extensive gas measurement facilities and controlled atmosphere Calorimeters.
Because the burning environment of the Cone Calorimeter is considered to be a
good representation of the majority of actual fire conditions, chemical sampling
is often done as a supplement to the standard test procedures. Some gases (CO,
CO2, H2O, total unburned hydrocarbons) can readily be
monitored with dedicated real-time gas analyzers. Other gases (HCN, HCl, HBr,
SO2, NOx, TDI) can be batch sampled, then analyzed by ion
chromatography. Alternatively, Fourier Transform InfraRed (FTIR) spectrometers
have been explored for real-time analysis of numerous gas species simultaneously
Table 1 Breakdown of types of laboratories
owning Cone Calorimeters
|Another research development has been the
construction of controlled-atmospheres Cone Calorimeters . The interests here
are three-fold: (1) the ability to conduct tests at lowered oxygen levels, or in
pure nitrogen, can provide significant additional insights for the polymer
development chemist. (2) In some aerospace applications, atmospheres with oxygen
concentrations > 21% are used; materials flammability should then be studied
under those actual, more hazardous, conditions. (3) During various phases of a
fire, some combustion takes place in vitiated air streams. Such burning behavior
can be quantitated with a controlled-atmospheres Cone Calorimeter .
Instruments capable of controlled-atmospheres work have been placed into service
at NIST, NASA, Dow Chemical and other laboratories.
Figure 2 Yearly number of
publications based on Cone Calorimeter research
|Turning from the development of the Cone
Calorimeter to its utilization, a very large number of research projects have
been conducted during the last decade by the use of the Cone Calorimeter. Space
does not permit discussing them in detail, but a complete bibliography has
recently been published which provides citations to the papers and gives brief
details on each . It is of interest to look at the total number of papers
which have been published that rely on Cone Calorimeter measurements. Fig. 2
shows that in the last few years more than 50 papers a year can be counted. This
is not surprising. During the 1970s it was felt that heat release rate was
one of the useful variables describing fire. By the late 1980s it was
realized that it was the most important single variable needed to
describe fire hazard .
|The first standard to be published describing the use of the
Cone Calorimeter was a draft standard (in their terminology a "proposal")
published by the American Society for Testing and Materials (ASTM) in 1986. It
carried the designation of P 190 and is now obsolete because ASTM have
subsequently published a full standard describing the Cone Calorimeter. The full
standard was first issued by ASTM in 1990 under the designation "Standard Test
Method for Heat and Visible Smoke Release Rates for Materials and Products using
an Oxygen Consumption Calorimeter (ASTM E 1354-90)." Slight amendments were made
in 1991 and 1992, with the current edition being E 1354-92. It is noteworthy
that the ASTM standard does not merely refer to the measuring of heat release
On the international scene, the International Organization for
Standardization (ISO) had been seeking to develop a bench-scale HRR apparatus
ever since the mid-1970s. Efforts were commissioned in the UK to have an
apparatus designed to this purpose, but success was not achieved. In the early
1980s ISO revisited this issue, and the convener of its Working Group ISO TC
92/SC1/WG5, Dr. Marc Janssens, conducted a world-wide canvass to determine if an
apparatus suitable to ISO could be found already designed and operational
somewhere. The ISO assessment was that the NBS Cone Calorimeter was the best
apparatus upon which to base the needed ISO standard for heat release rate. ISO
prepared a document which was based largely on the ASTM standard, but with two
important exceptions: the measurement for smoke and ignitability measurements
were assigned to different ISO Working Groups and, thus, could not be included
in the same process of developing the ISO standard. In 1990 ISO published the
Cone Calorimeter method as a draft international standard DIS 5660. This was
approved for publication as a final standard, ISO 5600. The published document
is expected to be ready in June 1993.
The work on the laser smoke measurement proceeded in ISO by
separate channels. A round robin was completed and ISO have approved that a
document be prepared for DIS voting. ISO have also approved that a document be
developed for a simplified `mass loss apparatus' which uses the heater and the
load cell from the Cone Calorimeter but not the other measurement systems. Such
a device is seen to have potential uses for screening, quality control and
production monitoring. For ignitability measurement, ISO currently prescribes
test ISO 5657, which uses a cone heater similar, but not identical, to the one
on the Cone Calorimeter. ISO have agreed to study the similarities and
differences between these instruments and to determine whether the ignitability
function could be just as well given over to the Cone Calorimeter, as is in the
ASTM standard. This work item, however, has not progressed much
In the US, some more specialized standards based on
the Cone Calorimeter have also recently been issued. Both ASTM  and the
National Fire Protection Association (NFPA)  have issued standards dealing
with the use of the Cone Calorimeter for testing furniture items. The US
Department of Defense published a standard for composite materials 
requiring the use of Cone Calorimeter testing. NASA issued a standard  based
on the use of the controlled-atmospheres Cone Calorimeter for testing materials
for space vehicles. In Canada, building code requirements for non-combustibility
are slated to be revised, with the Cone Calorimeter being used for testing in
that application. Similarly, US building codes are also starting to issue
product approvals based on such testing, although so far only on a case-by-case
|Applications of the Cone Calorimeter
|Many older devices for assessing flammability were not based on
realistic fire conditions, nor were measurements taken which have quantitative
engineering significance. As a result, they could only be used to pass or fail a
specimen according to some regulatory requirement. Because its design and its
data are firmly based on an engineering understanding of fire, the Cone
Calorimeter has wider applicability. It can be used to
- Provide data needed for state-of-the art fire models;
- Provide data used to predict real-scale fire behavior by
means of simple formulas or correlations;
- Rank order products according to their performance; or,
- Pass or fail a product according to a criterion level.
The earliest applications of Cone Calorimeter data have been in
the polymers industry. Hitherto, in the US manufacturers typically have relied
either on limiting oxygen index (LOI)  tests or on UL94 . The latter is
a simple Bunsen-burner type test which gives only pass/fail results; it is clear
that quantitative information useful for polymer development does not come from
such a test. The former, however, does give quantitative results and uses what
would appear to be a suitable engineering variable. Again, however, a recent
study has clearly demonstrated that the results, while quantitative, are not
capable of even correctly rank-ordering according to actual fire behavior .
By contrast, it has been shown quite clearly that heat release rate is the
single most important variable describing the hazard of the actual fire .
Thus, there remains the issue: How do we best collect or analyze bench-scale HRR
data in order to predict the full-scale HRR?
For purposes of rank ordering and simplified quantification, it
was originally proposed in 1984  that a variable should be considered which
expressed here is the peak HRR divided by the time to ignition. Data obtained in
the course of various room fire test programs had shown that this variable could
account for-approximately-the heat release occurring from surfaces over which
flame is spreading. This is possible since the flame spread process and the
ignition process are governed by the same thermophysical properties of the
material. More recently, the late R. V. Petrella has proposed  to the
plastics industry that a two-dimensional rating scale be considered, with the
variable described above placed on one axis and the total heat released during
test placed on the other axis. Besides knowing how to analyze the data for such
applications, the other important information needed is at what heat flux should
the specimen be tested. This question is not simple; some necessary
considerations are treated in .
Beyond rank ordering and simple product comparison, there have
been already a number of noted successes where Cone Calorimeter HRR data were
used for more detailed predictions:
- Combustible wall and ceiling linings in rooms. This is a
very difficult problem, but very impressive success was achieved in the
European 'EUREFIC' research program . It is especially noteworthy that
data from only the Cone Calorimeter were required in making these real-scale
predictions. Another approach to this same problem was developed at Lund
- Upholstered furniture. This problem was addressed at NIST in
two separate research projects ,. Work is continuing in this area both
at NIST and in a large European Community project in Europe.
- Electric wire and cable. In most countries the large scale
fire test for these products is a vertical cable tray test. In a research
project conducted at BFGoodrich, it was demonstrated that the Cone Calorimeter
can successfully predict the HRR results from several such large tests .
- Non-combustibility and 'degrees of combustibility' of
building products. Work has been done for the Canadian building code committee
establishing the use of Cone Calorimeter data in those areas where the code
had specified either non-combustibility tests or material-specific
These and other more specialized applications are
discussed in detail in a recent textbook which comprehensively examines heat
release in fires .
|Many earlier fire test methods had particularly
simple data outputs. Typically, only one or two numbers would need to be
reported or, possibly, one or two curves. The Cone Calorimeter, however,
produces large amounts of data: curves of heat release, smoke, and mass loss,
also often of CO, CO2, and other gas yields. Added to this are a
large amount of scalar data, in the vicinity of 100 variables. These are all
data which are readily and automatically collected by the software used with the
Calorimeters. The issue that the engineering community faced, however, was data
interchange and data inputting into fire models and calculation methods. Data of
differing formats can always be converted but this involves significant time and
effort. Furthermore, the data achieve a much greater utility when they are
available through a database, where searches can be made using logical
conditions and Boolean variables. The Cone Calorimeter is not alone in being
able to use such data handling facilities-other fire tests can also very
usefully be handled by means of a database, even when their data output is more
limited. To facilitate this process, NIST, the Fire Research Station, US Navy,
Norway's SINTEF, and a number of other organizations cooperatively agreed upon
data formats to be used for exchanging and storing fire test data . A
companion computer program was developed which provides for the database
operations, graphics, and report output . Even though motivated originally
by Cone Calorimeter data needs, the system encompasses many different types of
tests not just this one.
|Despite the impressively large amount of research done so far,
it is well anticipated that a great deal more research will be done on many Cone
Calorimeter applications in the years to come. It is a tool which has already
proven its utility to industry, testing laboratories, and research workers, but
the surface has barely been scratched as far as potential uses are concerned.
With the ISO issuing of the standard ISO 5660, interest in the test and
development of applications will increase significantly, especially in countries
which adopt ISO standards. Some important trends anticipated for the coming
- Increased utilization in polymer development, taking over
some of the existing role of thermal analysis (TGA, DSC, etc.) equipment.
- Adoption into building codes and other regulations for
various applications where the requirements would be better served by a HRR
approach (supplemented, where necessary, with the numerous other data
routinely available from a Cone Calorimeter test). In many cases, the
currently-prescribed tests are of a much larger scale and are costlier to
perform; thus cost savings could be seen, in addition to improved validity of
- An increased number of product types for which
bench-scale/full-scale predictive correlations or algorithms become available.
- Increased interest in Cone Calorimeter data by fire
protection engineers, as fire models become more comprehensive, more
successful, and more widely used. Cone Calorimeter data will be necessary with
most of them as part of the input data.
- Increased use of the standard data formats
developed under FDMS. A number of commercial testing laboratories are already
exploring the arrangement whereby clients would be given their data both in
the form of the traditional printed report and also in the form of a floppy
disk of their data in FDMS format. This will allow the client to easily
compare on the computer his current data against his other data and also
against any databases supplied by public-interest research
- Huggett, C., Estimation of Rate of Heat Release by Means of Oxygen
Consumption Measurements. Fire and Materials 4, 61-65 (1980).
- Babrauskas, V., Development of the Cone Calorimeter A Bench-Scale Heat
Release Rate Apparatus Based on Oxygen Consumption (NBSIR 82-2611). [U.S.]
Natl. Bur. Stand. (1982).
- Babrauskas, V., and Mulholland, G., Smoke and Soot Data Determinations in
the Cone Calorimeter, pp. 83104 in Mathematical Modeling
of Fires (ASTM STP 983). American Society for Testing and
Materials, Philadelphia (1987).
- Nyden, M.R., and Babrauskas, V., Use of FTIR Spectroscopy for
Multi-Component Quantitation in Combustion Technology, pp. 107-1 to 107-4 in
1987 Combined Technical Meetings: Eastern Section, the Combustion Institute,
and The Center for Fire Research Annual Conference on Fire Research,
Gaithersburg, MD (1987).
- Kallonen, R., Smoke Gas Analysis by FTIR Method. Preliminary
Investigation, J. Fire Sciences 8, 343-360 (1990).
- Babrauskas, V., Twilley, W.H., Janssens, M., and Yusa, S., A Cone
Calorimeter for ControlledAtmospheres Studies, Fire and Materials
16, 3743 (1992).
- Mulholland, G., Janssens, M., Yusa, S., and Babrauskas, V., The Effect of
Oxygen Concentration on CO and Smoke Produced by Flames, pp. 585-594 in
Fire Safety Science Proc. of the Third International Symposium,
Elsevier Applied Science, London (1991).
- Babrauskas, V., Cone Calorimeter Annotated Bibliography 1982-1991 (Tech.
Note 1296). Natl. Inst. Stand. and Technol., Gaithersburg (1992).
- Babrauskas, V., and Peacock, R.D., Heat Release Rate: The Single Most
Important Variable in Fire Hazard, Fire Safety J. 18, 255-272
- Standard Test Method for Determining the Heat Release Rate of Upholstered
Furniture and Mattress Components or Composites Using a Bench Scale Oxygen
Consumption Calorimeter (ASTM E 1474-92), American Society for Testing and
Materials, Philadelphia (1992).
- Standard Method of Test for Heat Release Rates for Upholstered Furniture
Components or Composites and Mattresses Using an Oxygen Consumption
Calorimeter (ANSI/NFPA 264A). National Fire Protection Assn., Quincy, MA
- Fire and Toxicity Test Methods and Qualification Procedure for Composite
Material Systems used in Hull, Machinery, and Structural Applications inside
Naval Submarines, MIL-STD-2031 (SH). Department of Defense, Philadelphia, PA
- Flammability, Odor, Offgassing, and Compatibility Requirements and Test
Procedures for Materials in Environments That Support Combustion (NHB
8060.1C). Office of Safety and Mission Quality, National Aeronautics and Space
Administration, Washington (1991).
- Standard Method of Test for Flammability of Plastics using the Oxygen
Index Method (ASTM D 2863). American Society for Testing and Materials,
- Tests for Flammability of Plastic Materials for Parts in Devices and
Appliances (UL 94). Underwriters Laboratories, Northbrook.
- Weil, E.D., Hirschler, M.M., Patel, N.G., Said, M.M., and Shakir, S.,
Oxygen Index: Correlations to Other Fire Tests, Fire and Materials
16, 159-167 (1992).
- Babrauskas, V., and Peacock, R. D., Heat Release Rate: The Single Most
Important Variable in Fire Hazard, Fire Safety J. 18, 255-272
- Babrauskas, V., Bench-Scale Methods for Prediction of Full-Scale Fire
Behavior of Furnishings and Wall Linings, Technical Report 84-10, Society of
Fire Protection Engineers, Boston (1984).
- Petrella, R. V., presentation to The Society of the Plastics Industry,
Inc., Miami, FL (December 1992).
- Babrauskas, V., Specimen Heat Fluxes for Bench-scale Heat Release Rate
Testing, paper presented at INTERFLAM '93, Oxford (April 1993).
- Wickström, U., and Göransson, U., Full-scale/Bench-scale Correlations of
Wall and Ceiling Linings, Fire and Materials 16, 15-22 (1992).
- Karlsson, B., A Mathematical Model for Calculating Heat Release Rate in
the Room Corner Test, paper presented at ASTM International Symp. on Fire and
Flammability of Furnishings and Contents (1992).
- Babrauskas, V., and Krasny, J.F., Fire Behavior of Upholstered Furniture
(NBS Monograph 173). [U.S.] Natl. Bur. Stand. (1985).
- Parker, W.J., Tu, K.-M., Nurbakhsh, S., and Damant, G.H., Furniture
Flammability: An Investigation of the California Technical Bulletin 133 Test.
Part III: Full Scale Chair Burns (NISTIR 4375). [U.S.] Natl. Bur. Stand.
- Hirschler, M.M., Electric Cable Fire Hazard Assessment with the Cone
Calorimeter, pp. 44-65 in Fire Hazard and Fire Risk Assessment (ASTM
STP 1150). American Society for Testing and Materials, Philadelphia (1992).
- Richardson, L.R., and Brooks, M.E., Combustibility of Building Materials,
Fire and Materials 15, 131-136 (1991).
- Richardson, L.R., Determining Degrees of Combustibility of Building
Materials-National Building Code of Canada, pp. 1-12 in Proc. First Intl.
Fire and Materials Conf., Interscience Communications Ltd, London (1992).
- Babrauskas, V., and Grayson, S.J., eds., Heat Release in Fires,
Elsevier Applied Science Publishers, London (1992).
- Babrauskas, V., Peacock, R.D., Janssens, M., and Batho, N.E.,
Standardizing the Exchange of Fire Data The FDMS, Fire and Materials
15, 85-92 (1991).
- FDMS computer program, developed by Dark Star Research Ltd with funding of
FRS. Available from S.A. Ames, Fire Research Station, Borehamwood, Herts. WD6