Survey of the Literature on Safety of

Residential Chimneys and Fireplaces

United States Department of Commerce

National Bureau of Standards

Miscellaneous Publication 252
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Printing Office, Washington, D.C., 20402.
UNITED STATES DEPARTMENT OF COMMERCE • Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS • A. V. Astin, Director

Survey of Literature on the Safety of

Residential Chimneys and Fireplaces

Harry Shoub

Conducted Under the Technical Studies Program of the Federal Housing Administration

National Bureau of Standards Miscellaneous Publication 252

Issued December 17, 1963

For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 - Price IS cents
Library of Congress Catalog Card Number: 63-62134
Survey of Literature on the Safety of Residential Chimneys and

Fireplaces 1

Harry Shoub

A search was made of recent technical literature on chimneys and fireplaces to determine

what information was available on questions concerning their safety from fire hazard. The

survey covered types of construction and materials proDOsed or currently in use with several

types of fuel. The reports included investigations of heat transmission through chimney and

fireplace walls, the effects of thermal shock on flue materials, and the required spacing of combustibles from the heated walls. The bibliography presented contains brief reviews of some of the works.

1. Introduction

Chimneys and fireplaces in some form, ranging

from crude to elaborate, have been used since

very early times, but questions concerning their

design and construction, particularly with regard

to features relating to fire safety, continue to be

raised. As a preliminary to proposed technical

investigations, it appeared that a literature sur- vey of published and unpublished data available

to the National Bureau of Standards might prove

fruitful in providing information in some areas of concern. While the primary objective was to present works relating to problems of fire hazard,

collateral information on associated subjects of

interest has been briefly included.

Although several highly significant earlier refer- ences are included, the bibliographic study was

confined mainly to those papers issued since about

1950. It was thought that these would most

likely yield useful data which were not yet widely

disseminated, and would also give an indication of the scope of work in progress or recently

completed.

The bibliography of works on chimneys and fireplaces is presented in two sections, the first containing those papers available for review, for

which a brief summary or indication of the contents is given, the other listing works which were

not readily available under the limitations of

search set for this project, but which were believed

to contain information of interest. Since they are

closely associated, papers on both chimneys and

fireplaces are presented together in reverse chronological order.

Mention must be made of some early works on

fireplaces and chimneys. Three are of considerable

significance, probably the most remarkable being

Count Rumford's "Chimney Fireplaces," which

appeared in 1796. This book reports the results of

scientific investigation, and contains rules for the

construction of fireplaces that are valid and in use today. Benjamin Franklin contributed to the

science of domestic heating with the publication,

in 1745, of his "Papers on Philosophical Subjects."

Even earlier was the work of M. Gauger, "La

Mecanique du Feu" ("The Mechanics of Fire")

published in France in 1709. An English translation was made by J. T. Desaguliers in 1715.

Works such as these may well be the basis of the

"conclusions based on long experience" often

found in papers relating to heating problems.

2. Bibliography of Publications Reviewed and Abstracted

1. Fact-Finding Report on Masonry Fireplaces,

for Federal Housing Administration, Underwriters'

Laboratories, Inc. File USNC 24, June 29, 1962,

and October 18, 1962: Tests were made on a masonry fireplace to determine what temperature

would be obtained on the masonry surfaces and on

combustible materials adjacent to or in contact

with the masonry. Fuels in the tests of the June

report were wood brands (input 32 lb/hr), charcoal (28 lb/hr), and logs (26 lb/hr). The tests were discontinued before equilibrium temperatures were reached, as the temperature of combustible

materials, especially those at the back wall, ex- ceeded established maximum safe limits. The

1 This paper was prepared under the sponsorship of the Federal Housing

Administration.

report is well supplied with plans of the test

structure, and is documented with extensive test

data. The October report presents data on additional tests with charcoal and logs with fuel rates

for both at approximately 10 and 20 lb/hr. Except for the test with the larger quantity of charcoal, firings were continued for 12 hr. A

comparison is made of temperatures of combustibles in contact with the masonry and at % in.

spacing for the two firing rates, and for 4-in.- and

8-in. -thick masonry walls.

2. Residential Chimneys of Non-Traditional

Design, Institute TNO voor Bouwmaterialen en

Bouwconstructies (Netherlands) 1961-1: Temperature difference between the outer and inner wall

1
surfaces of a concrete chimney with round flue

12 cm in diameter depends on the wall thickness.

With the heat transmission of the concrete not

higher than 0.4 kcal/meter hour °C and a flue gas

temperature of 600 degrees C above the ambient,

this difference amounts to 146 degrees C for a wall

thickness of 6 cm and 95 degrees C for 8 cm. Some of the advantages of concrete chimneys

with ceramic flue liner over the traditional brick

chimney are fewer cracks and lower temperatures

on the outer covering. Unlined concrete chimneys

are characterized by low resistance to deterioration

from heat and to flue gas attack. Recommendations in the paper are for the use of horizontal

reinforcing in unlined chimneys, and for concrete

with low water-cement ratio and quartz-free

porous aggregate.

3. Contribution to the Study of the Behavior

Under Heat of Concretes for Chimney Flues,

M. L. Boy, Centre Scientifigue et Technique du

Bdtiment (France), No. 51, Cahier Ifi8, August

1961: Concretes resistant to heat effects and thermal shock for use in chimney flues are described.

Temperature gradients in chimney walls are great

enough to engender high thermal stresses. Concrete flue liners should not be subjected to thermal shock until several months after fabrication.

It is important to choose an aggregate with a low

coefficient of thermal expansion.

4. Flues (Approval of New Materials and NonTraditional Methods of Construction), Cahiers

du C.S.T.B. {France), No. 49, F.4, 1961, 392:

Approval tests are described for various proprietary concrete chimney flue blocks, mainly with

pozzuolanic aggregate. Cracking of some flues

occurred from thermal shock. Determinations

were made of air permeability coefficients of the

blocks.

5. Station for Tests of Chimney Flues, Centre

Scientifigue et Technique du Bdtiment (France),

No. 47, Cahier 879, December 1960, p. 14: Tests

were made of the effect of thermal shock from flue

gasses at 400 and 500 °C on concrete block chimney flues. Gas permeability measurements were

made before and after the blocks were subjected

to the thermal shock.

6. Chimney flues of Concrete Block, Centre

Scientifigue et Technigue du Bdtiment (France),

No. 44, Cahier 848, June 1960: Tests were made

of lightweight concrete chimney block units,

some with coverings of 1 or 2 cm of plaster.

Temperature data are given for the interior and

exterior faces of the flue for various flue gas

temperatures, and the effect of heat on various

concretes is described. Fuels were coal, wood,

and oil.

7. Chimneys, Tests on Masonry Residential

Type, National Board of Fire Underwriters Special

Interest Bulletin No. 14, May 1960: Tests were

conducted at Underwriters' Laboratories, Inc.,

on a standard (National Building Code) masonry

chimney. Excessive heat buildup noted on ceilings placed in contact with the chimney indicated

the necessity of providing an open airspace

between the chimney wall and combustible material. At 2 in. from the chimney, temperatures

were lower on sheet enclosure material than on

wood studs, probably because of the larger

radiating surface area of the sheet. Increasing

the chimney wall thickness by 4 in. where the end

of a wood girder was in contact prevented a hazardous temperature rise on the wood.

8. Performance of Type B Gas Vents for GasFired Appliances, L. M. Kline and H. Witte,

Underwriters' Laboratories, Inc., Bulletin of liesearch No. 51, May 1959: Tests were made to

determine the temperatures of flue gases passing

through different vent systems. Heat sources were a central furnace, water heater, floor furnace,

unit heater, and room heater. Four types of vent

pipes were used: double wall with y2 - and %-ia.

airspace, single wall, and asbestos-cement, mostly

of 3- and 5-in. diameter. Data are shown for

temperatures of flue gases at inlet of draft hoods

and vents, and temperature rises on vent pipe

walls and walls of vent pipe enclosures. Least

heat transmission was noted with double-wall

metal pipe with )i-m. airspace. A separate sec- tion of the report (Part II, by A. F. Matson,

R. E. Dufour, and J. F. Breen) contains a survey

of the ignition of wood exposed at elevated temperatures for long periods. It was concluded

from the evidence that such exposure should be

limited to a maximum temperature of 90 degrees F

above room temperature.

9. Testing of a Chimney, Gote Larsson, Statens

Provningsanstalt (Sweden), Meddelande 125, 1959:

Tests with brick chimneys indicate that combustible materials will be ignited if maintained

in continued contact with a chimney of 12 cm wall

thickness if the flue gas temperatures are 400 °C.

It appears that ignition of combustibles near chimneys occurs because of unsatisfactory chimney

insulation rather than from lack of tightness of

the chimney walls. Restraint of a chimney

during a chimney fire can cause cracks to be

formed through the entire structure. Chimney

brickwork should not be used to support building

members unless the chimney has an internal,

independent flue.

10. Temperature of the Wall behind a BackBoiler Fire, L. L. Fox and D. Whittaker, J.

Institution of Heating and Ventilating Engineers,

London, Vol. 26, 1958, pp. 80-85: Model bylaws

state that the thickness of the rear wall of a

fireplace recess shall be not less than 4 in. for

external wall, or 8% in. for internal. On a bare

9-in. brick back wall, the highest temperature on

the outside surface was 130 °F with coke fuel and

2
150 °F with coal. Burning house coal at the

greatest possible rate for 12 hr, a boiler fire produced a temperature of 175 °F on a bare outside

wall 9 in. thick, and 305 °F on a 4%-in. wall.

With a 1-in. board cemented to the brick, temperatures of 265 and 570 °F were attained on the

brick for the two wall thicknesses.

11. An Analysis of Survey Information on

Chimney Fires, Joint Fire Research Organization {U.K.), May 1957: As coal is the most widely

used of all fuels in the United Kingdom, there is little available evidence to indicate the contribution of other fuels to the incidence of chimney

fires. The paper suggests that in view of this

widespread use of coal for domestic heating,

frequent cleaning of the lower part of a chimney

may be an important factor in preventing fires.

12. Chimney Stacks Made of Precast Concrete Units, G. Heinicke, Betonsteinzeitung Wiesbaden, Vol. 22, No. 12, Dec. 1956, pp. 718-726:

Requirements for chimney construction of concrete

block are described, as well as the technical and

economic advantages of the use of this material.

Methods of framing roof members around a chimney are illustrated.

13. Residential Fireplace Design, Structural

Clay Products Institute, Technical Notes on Brick

and Tile Construction, Vol. 6, No. 10, Oct. 1955:

The paper includes a description of fireplace parts,

National Building Codes recommendations, and

a table of flue sizes for different sizes and types

(single face, two face, etc.) of fireplaces.

14. Some Measurement of Temperatures of

Metal Flues of Domestic Heating Appliances,

L. L. Fox and D. Whittaker, J. Institution of

Heating and Ventilating Engineers, London, Vol.

23, 1955, pp. 183-192: Three types of small solidfuel appliances were tested in normal operation

with coal and coke fuels. Temperatures are given

for flue gases and surfaces of sheet metal flue pipe,

with higher temperatures recorded for coal. In a

closed fire with solid fuel, considerable and rapid

changes in temperature are possible. There is some mention of the fire hazard to timbers adjacent to flues.

15. Thermal Insulation and Fire Protection of

Small Chimneys, Paul Becker, Ingeni0ren, Copenhagen, Vol. 64, No. 42, 1955, pp. 827-881: Chimneys of various masonry constructions, times of

curing, flue diameters, and outer protections were

tested. Fuels were anthracite, coke, lignite, peat,

wood, oil, and city gas. The paper gives heat

transmission data, and shows examples of good and

bad practice in chimney design.

16. Tests on Types of Chimneys With Regard

to Fire Resistance, Gerhard Hansen, Ingeni0ren,

Copenhagen, Vol. 64, No. 42, 1955, pp. 8S2-8SS:

Chimneys of lightweight concretes (pumice, cinder,

etc.) were tested with flue gas temperatures to

1000 °C using a small heating stove source. The

formation of dangerous cracks is described. The

performance of a conventional brick chimney was

used as reference in evaluating the results.

17. ACI Standard Specification for the Design

and Construction of Reinforced Concrete Chimneys (ACI 505-54), American Concrete Institute J.

26 (1), 1954-55, pp. 1-48: Formulas are given for

determining temperature gradients through concrete chimney shells.

18. The Heating of Panels by Flue Pipes, D.J.

Lawson, L. L. Fox, C. T. Webster, Department of

Scientific and Industrial Research, Fire Offices

Committee (U.K.), Fire Research Special Report

No. 1, Her Majesty's Stationery Office, 1952:

Temperature rise on a vertical panel near a cylindrical radiating surface was computed. An as- bestos shield proved effective in reducing the

temperature of the panel, with a greater advantage

deriving from separation of the shield and the

panel. Separations greater than % in., however,

gave little additional temperature reduction.

Theoretical and experimental derivations were

made for heat transfer from flue pipes not enclosed or covered. The tests were made with

solid fuels.

19. Residential Chimney Design and Construction, Structural Clay Products Institute, Technical Notes on Brick and Tile Construction, Vol. 3,

No. 1, Jan. 1952: Tests were made of brick

chimneys 4 in. thick with standard 8- by 8-in.

flue liners. In a chimney where the flue lining

sections were not cemented and a space was left

between the lining and the brick, the airspace

appeared to have no effect on the operation, and

no appreciable insulating value. It was considered

preferable to bond the liner sections and fill the

space between liner and brick solidly with cement

mortar on the basis of the greater strength of

this construction and its ability to stay in place

when cracked. Standard construction and clear- ances from combustibles (NBFU) are recommended.

20. The Construction of Central Heating Flues,

M. Bergstrom, Teknisk Tidskrift, Stockholm,

80 (IS), 1950, pp. 288-94: Temperatures to 1300

°C were observed in chimney soot fires. Tests

were made of chimneys having inner and outer

shells of brickwork with an intermediate layer of

mineral wool. Concrete outer shells approximately 4 in. thick were also used. Inner lining

should be able to move freely when expanded by

heat. Minor cracking of inner shell was not found

to be important, provided outer shell remains

intact.

21. The Problem of the Flue From the Fireman's

Point of View, I. Stromdahl, Teknisk Tidskrift,

Stockholm, 80 (13), 1950, pp. 283-286: Tempera-
ture rise in flue fires may be very rapid, especially

with wood fuel. In a test, a temperature of 900

°C was observed in 3 min, 1300 °C in 15 min after

start.

22. Fires in Flues From the Point of View of

Insurance Companies, A. Sylven, Teknisk Tidskrift, Stockholm, 80 (18), 1950, pp. 286-288:

Fires of short duration seldom cause damage to a well-constructed brick chimney, even if very high

temperatures occur. The inner brickwork of a double-shelled brick chimney with mineral wool

filler withstood 10 soot fires with temperatures

reaching to 1400 °C before destruction.

23. Fire Hazard Tests With Masonry Chimneys, Nolan D. Mitchell, NFPA Quarterly, Vol.

43, No. 2, Oct. 1949: Tests were made of 21 different masonry chimneys constructed of brick,

tile, or concrete block units, either unlined or with

ceramic or vitreous enameled steel liners. Some

concrete block units had integrally cast liners.

Fuels were coal, wood, and gas. Unlined chimneys present greater fire hazards than do lined

ones. Round liners appear to have some advantage over rectangular ones. Liners should not be

rigidly fixed to the chimney wall. Units with

integrally cast liners developed cracks through

both the liner and outer wall. The space between

chimney wall and wood framing should be left

unfilled. Mineral wool fills between joists and

chimneys have in some cases caused ignition of the

wood. Wood plaster grounds should be removed,

and staying at floor or roof level should be limited

to contact with flooring or sheathing not more

than l}i in. from corners of chimney.

24. Performance of Masonry Chimneys for

Houses, R. K. Thulman, Technical Paper No. IS,

Housing and Home Finance Agency, Aug. 1949:

The criterion of safety to combustible materials

adjacent to a chimney is established as 90 degrees

F temperature rise on the combustible with flue

gas temperature of 1000 °F for 5 hr and 1400 °F for

1 hr. A substantial portion of the heat in the flue

gases is lost through the masonry in the area adjacent to the entrance of the breeching, probably because of turbulence. Introducing air into

the breeching reduces the temperature of flue

gases. Chimneys with mortar lining only appear

to be responsible for more fires than those with

ceramic flues. Insulation between flue lining and

outer shell reduces temperatures on the outside

wall. The paper recommends that contacts

between combustible construction and masonry

surfaces not already prohibited by building codes,

should be banned. Data are included for temperatures of flue gases, brick surfaces of fined and

unlined chimneys, and of wood in contact with

masonry and also at 2-in. spacing from the

masonry.

25. Clearances and Insulation of Heating Appliances, John A. Neele, Underwriters' Laboratories, Inc., Bulletin of Research No. 27, June 1945:

The heating of adjacent woodwork by stoves and

smokepipes is described. Safe maximum temperature for long-continued exposure of wood was

established as 90 degrees F above room temperature. In order not to exceed this maximum

rise, a clearance of 7 in. would have to be provided

between a wood panel and a smokepipe at 450 °F.

Thoroughly dried and slightly scorched wood

panels were found to develop higher temperatures on the surface than they did when new.

26. Temperatures Developed in Chimneys for

Low Cost Houses, NBS Technical News Bulletin

No. 328, Aug. 1944, V- 62: To establish performance requirements for tests of light-weight,

prefabricated chimneys, tests were conducted

with lined and unlined chimneys having 4-

in. -thick brick walls. In the surrounding structure,

floor joists were framed 2 in. away from the

chimney surface, but edges of floorboards and

nailing strips were placed in contact. After

approximately 13 hr for the lined chimneys, and

slightly less time for the unlined, and with flue

gas temperatures of 1100 °F and 900 °F, respectively, hazardous temperature conditions were

created on surrounding wood.

27. Observed Performance of Some Experimental Chimneys, R. S. Dill, P. R. Achenbach,

J. T. Duck, Heating, Piping and Air Conditioning,

Vol. 14, Apr. 1942, pp. 252-256: Tests were made

on two experimental, residential-type chimne3Ts operating at various stack heights, gas flows, and

inlet temperatures. Data are given for temperature gradients at different levels in the chimney,

which were of brick masonry with ceramic flue

liner.

28. Fire Hazard of Domestic Heating Installations, G. Q. Voigt, Bureau of Standards Research

Paper RP 596, Sept. 1933: Tests were made of

domestic stoves and furnaces and their pipes.

Temperature rise was determined on partitions,

ceilings, and floors, as well as the effect of some

protective materials. Ignition of wood could

occur from short-time exposure at temperatures

of 250 to 300 °C, or from long exposure at 150 °C.

Temperatures frequently exceeding 125 °C should

be avoided, but 150 °C may be tolerated

occasionally. Uninsulated smoke pipes passing

through combustible partitions require 4 in. of

vented airspace at the sides, or may be insulated

with 2 in. of mineral wool. Stoves having the

fire box or ash pit directly on the floor can transmit temperatures capable of igniting wood through

a 4-in. -thick brick base. With a 5-in. airspace

between stove and floor, the floor should be further

protected with %-in. asbestos or similar material

under sheet metal. The possiblity of igniting

wood forms left under brick or concrete arches

supporting fireplaces is indicated.

4
29. Recommended Minimum Requirements for

Small Dwelling Construction, Bureau of Standards

Building and Housing Publication No. 18, 1932,

pp. 19-22 and 78-89: Designs are given for chimneys and fireplaces, and methods of framing

combustible members around them. Ceramic flue

finings are preferable to parged brickwork. For

fireplaces, good draft design requires an effective area of flue of }{ 2 of the area of the fireplace

opening.

30. Prefabricated Metal Chimneys, National

Bureau of Standards, Fire Research Section, unpublished reports to Federal Public Housing Authority, District of Columbia Alley Dwelling Authority, and others, 1941-45: Tests were made with

prefabricated porcelain-enameled metal chimneys

for solid or liquid fuel furnaces in war-emergency housing. A limiting temperature rise

of 375 °F on the outer surface of the chimney

was established for a flue gas temperature of

1000 °F. Under this condition, combustible

framing and wood spaced 2 in. or more away from

the chimney was considered safe. Satisfactory

insulation of the chimneys was obtained with

asbestos paper plies totaling about 1% in. in

thickness and having a combustible content not

exceeding 5 percent. Some asbestos-cement pipe

coverings were also found to be capable of re- ducing heat transmission to the extent required

for safety to nearby combustibles.

3. Selected Publications Not Reviewed

31. The Fire Proof Chimney, Bayerischen Versicherungskammer (Germany), 1959.

32. Chimney Fires, Fire, London, 1958, 51 (639)

197, 200.

33. Chimneys and Fire Protection, A. H. Bergquist, Byggmastaren, Stockholm, 1958, 134

77-80.

34. Modern Flue and Chimney Construction,

Bldg. Mat., London, 1958, 18 (2), 69-70.

35. Experimental Observations Concerning Cracks

in Flues, Claudon and Tirel, Ann. Inst. Batiment, Paris, 1958, 11 (121), 40-52.

36. Thermal Stresses in Flues, J. Tirel, Ann.

Inst. Batiment, Paris, 1958, 11 (121), 28-39.

37. Gas Flues, Archt. (Build.) J., London 1958,

127 (3295), 624-634.

38. The Design of Domestic Open Fires, D. K.

Darby, Plumber, London, 1958, 80 (949)

45-50; (950) 43-44.

39. Structural Fire Protection, Fortschritte u. Forschungen im Bauwesen, Reihe D, Heft

27 Franckh'sche Verlagshandlung, Stuttgart, 1957. (Fire resistance of flues of

standard masonry and of lightweight con- weight concrete castings.)

40. Domestic Flues, P. Becher, Industries Thermiques, Paris, 1957 (11), 655-665.

41. Materials for Flues, A. Claudon, Industries

Thermiques, Paris, 1957 (11), 666-688.

42. Theory of the Construction of Chimney Flues,

R. Cadiergues, Industries Thermiques,

Paris, 1957 (11), 689-701.

43. The Cracking of Flues, Centre Scientifique et Technique du Batiment (France), Cahier

238, 1957.

44. Space Heating and Associated Fire Hazards,

Booklet No. 33, Fire Protection Assn.

(U.K.), London, 1957.

45. Oil Fired Domestic Boilers and Air Heaters

for Hot Water Supply and Space Heating:

Safety Recommendations, Booklet No. 31,

Fire Protection Association (U.K.), London,

1957.

46. Maximum Temperatures Attained in Chimney Flues, A. Claudon, Industries Thermiques, Paris, 1957, 3 (1), 21-40.

47. Lightweight Concrete Shaped Blocks of up to

700 cm2 Section, Standard DIN 18150,

Deutscher Normenausschuss, Berlin, 1956.

48. Fire Tests on Domestic Chimneys, H. Seekamp and K. Mohler, Verl. von Wilm.

Ernst u. Sohn, Berlin, 1956.

49. Aluminum-Sheet Chimneys, Light Metals

Bull, London, 1956, 18 (8), 316.

50. Flue Pipes and Combustible Materials, Fire

Prot. Assn. J., 1956, (33), 207.

51. Flue Piping Causes Fire, Fire Protection

(Rev.), London, 1956, 19 (185), 178.

52. Chimney Fires, Prot. Civile, Paris, 1956,

(23), 46-47.

53. Temperatures on a Wood Ceiling about a Furnace Plenum, R. Ditsworth, Heat.

Air Condit. Contract., Tarrytown, N.Y.,

1955, 27, (2) (Issue 715), 31-37.

54. The Protection of Floors under Fireplaces, F.

Mayer, Osterr. Feuerwehr, Vienna, 1955,

9 (1), 8-9.

55. Tentative Code of Minimum Obligatory

Conditions for the Fixing of Fire-Grates

and Associated Conduits, Ann. Inst. Batiment, Paris, 1955, 8 (94) Supp.

56. Design of Heating and Ventilating Systems,

F. W. Hutchinson, The Industrial Press,

New York, 1955.

57. A Guide to Current Practice, Inst, of Heat.

Vent. Engrs., London, 1955.

58. Asbestos-Cement Flue Pipes and Fittings,

Light Quality, BS 567, British Standards

Institution, London, 1954.

59. Domestic Fireplaces and Chimneys, Commonwealth Experimental Bldg. Sta., Dept. of

Works and Housing, Australia, Notes on

the Science of Bldg. No. SB 31, Chatswood,

N.S.W., 1954.

60. Prefabrication in Traditional House Building

I, N. S. Pippard and W. G. Buckle, Prefab5
rication, London, 1954, 1 (7), 15-18 (prefab, brick chimney stack).

61. Fire Incidents With Fireplaces, Flue Pipes and

Chimneys, R. Quester, Osterr. Feuerwehr,

Vienna, 1953, 7 (3), 47-7, 49.

62. The Hazard of Domestic Fire, J. F. Fry,

J. Roy. Inst. Brit. Archt., London, 1953,

61 (1), 18-20.

63. Fire Tests on Chimneys, S. Ausobsky, Osterr.

Feuerwehr, Vienna, 1952, 6 (12), 234-236.

64. Structural Timber under the Hearth, Fire

Prot. Assn. J., London, 1952, (19), 307-308.

65. Flue Pipes and Hearths, Norsk Brannvern

Forening, Oslo, Sept. 1952.

66. New Documents on Flue Construction,

Ribaud, Puteaux, Fournol and Gouffe,

Centre Scientifique et Technique du Batiment (France), Cahier 111, 1951.

67. Regulations and Instructions on the Venting

of Domestic Gas Heathing Appliances,

O. Rosier, Gas, Wasser, Warme, Vienna

1951, 5 (1), 6-16.

68. Domestic Chimneys, P. Becher, Statens Byggeforskningsinstitut, Studie No. 6, Copenhagen, 1951.

69. Fire Resistance Tests on Chimney Blocks

and Glass Panels, K. Walz and J. Strey,

Tonindustrie Zeitung, Goslar (Ger.), 1951,

75 (13/14), 203T208.

70. Flues for Domestic Appliances Burning Solid

Fuel, Brit. Stds. Inst., Council of Codes of

Practice for Bldgs., CP 131.101, London,

1951.

71. Domestic Hearths. Fires Due to Defects,

Fire Prot. Assn. J., London, 1951, (12),

Jan. 9-11.

72. Three Hazards That Need Watching, Doors,

Flues, Water Heaters, Fire Protection,

London, 1951, 14 (130), 317-318.

73. Smoky Chimneys, Bldg. Research Sta. Digest No. 18, HMSO, London, May 1950.

(Design of fireplaces and flues.)

74. Chimney Constructions and Dimensions of

Bricks, Virtala and Koskela, Valton Teknillinen Tutkimuslaitos, Tiedoitus 40 and

43, Helsinki, 1947.

75. Drawings of the Principles of Construction of

the Swedish Fire Prevention Assn., Svenska

Brandskyddsforeningen, Stockholm, 1946

(fireplaces and flues)

.

76. Precast Concrete Flues, Concrete Building,

London, 1946, 21 (8), 103-107.

77. Fire Hazards of Chimneys and Flues, Technical Information Sheet 1001, Fire Protection Assn., London.

4. Information and Conclusions From Reference Sources

An examination of the material in the reviewed

publications indicates that information is available on several aspects of the problem of fire

safety of chimneys and fireplaces, particularly on

the advantages of different types of chimney

construction blocks and liners, and on the conditions under which temperatures hazardous to

combustible materials may develop on the outer

surfaces of the structures.

Several types of chimney and flue liner arrangements, of varying degrees of suitability, are described in the papers. Brick chimney liners, or even better, chimneys having inner and outer

shells of brick with mineral wool separation were

reported as able to take the thermal shock of

repeated hot fires of short duration [20, 22]. 2 Ceramic flue liners were recommended by several

investigators [2, 23, 29] as these are reported to

be subject to fewer cracks than brick linings or those constructions without linings. They were

also found to give a lower temperature rise on the

outer surface. There is indication of a definite

advantage in having the inner lining free to move

independently of the outer shell [9, 20, 22, 23]

to minimize stresses arising from thermal differ- ences and possible restraint of the outside wall.

However, in one report [19] it is stated that a grouted liner is preferable because of its greater

stability when cracked. Round flue liners are

1 Figures In brackets indicate papers in the bibliography, Section 2, of this report.

6

said to offer a reduction in stresses due to thermal

effects, and to give better draft performance than

those of other cross sections [2, 23].

Unlined chimneys, made of lightweight concrete (pumice or cinder aggregate), were reported

as subject to the development of dangerous

cracks which could allow the passage of hot gases

or flame [4, 16]. Some control of such cracking

was reported possible by the use of horizontal

reinforcing [2]. Concrete units having integrally

cast liners developed cracks through both the

liner and the masonry wall [23]. The resistance

of concrete to heat and attack by flue gases is reported as lower than that of ceramic materials

Concrete chimney block units may be successfully used if the aggregates have a low coefficient

of expansion [2, 3], and the concrete is sufficiently

aged [3]. Certain proprietary flue blocks, mainly

with pozzuolanic aggregate, were found suitable

[3-6]. The use of concrete flue blocks was re- ported as offering some technical and economic

advantages [12].

Tests on prefabricated chimneys have indicated

that units of double-wall metal pipe with %-in.

airspace had the least heat transmission [8]. Porcelain-enameled metal chimneys (for solid or

liquid fuel) when insulated with about 1% in. of

asbestos paper plies could meet the requirement

of a limiting temperature rise of 375 degrees F
on the outer surface when the flue gas temperature

was 1000 °F [30].

The conditions under which hazardous temperatures may develop on the outer surface of

masonry chimneys are described in several reports

[7, 9, 26]. Temperature data for the exterior

face of a flue at various flue gas temperatures

are given [6, 15]. Temperatures reported as hazardous were also noted on fireplaces, particularly on back walls [1, 10]. Tests have indicated

the necessity for maintaining an air space between

wood-framing members and a chimney [7, 9,

26, 28]. Ignition of wood has occurred in some

cases where a mineral wool filling was used in the

2-in. space between joists and chimney [23].

Temperatures described as hazardous were measured on the edges of floorboards or ceilings in

contact with brick chimneys [7, 26], but staying

of chimneys may be allowed by contact with

flooring or roof sheathing not more than \%

in. from the corners of a chimney [23]. On a standard masonry chimney, increasing the wall

thickness by 4 in. where a wood girder was in

contact, reduced temperature rise on the wood to

acceptable limits [7]. Temperatures capable of igniting wood have

been measured through a 4-in. brick base under

the firebox of a stove directly on the floor, and by

analogy this condition is applicable to fireplaces

[28]. Thus, the practice current in some areas, of

supporting a fireplace on a frame structure, could

be hazardous.

It has been recommended that exposure of wood

for long periods at elevated temperatures should

be limited to a temperature rise of 90 degrees F

above room temperature [8, 24]. These refer- ences also report that ignition temperatures of

wood have been significantly lowered under

continued exposure. It was noted that dried and

scorched wood developed higher temperatures

on the surface when exposed to heat than did

new wood [25].

While the data available in the paper is pertinent to some of the problems of fire safety,

the tests described were generally of limited scope

and not applicable to all aspects of even a single

problem. Differences in construction practices,

fuels, and methods of heating further limit the

usefulness of the reports.

Further work could be done on resolving cer- tain contradictions in the information, especially

in the fields of grouting of chimney liners and the

effect of filling airspaces between heated surfaces

and combustibles with mineral wool insulation.

More knowledge also would be useful on the

effect of prolonged exposure of wood on its ignition temperature. The hazards of chimneys and

fireplaces could be further investigated to determine to what extent the formation of cracks

through the structure is a source of danger.

Finally, as it is the goal of much research, a study

could be made leading to the development of

new materials and products, for chimneys a permanent lightweight block not requiring a liner or additional insulation, and for fireplaces a substitute for the refractory lining.

Chimneys and fireplaces have been long used,

but systematic investigations of fire safety, long

left to chance and the saving feature of massive

construction, have only recently been undertaken.

Much remains to be done to gain the knowledge

required to solve these problems in a manner

consistent with assuring the best performance

of the structures.

U.S. GOVERNMENT PRINTING OFFICE ; 1963 O—708-213

7

U. S. DEPARTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

A.'V. Astin, Director

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