consideration of safe distance of standard fire test furnace of building elements

7/30/2019 Consideration of Safe Distance of Standard Fire Test Furnace of Building Elements

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Journal of Applied Fire Science Issue: Volume 14, Number 2 / 2005-2006 Pages: 125 - 135

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Consideration of safe distance of standard fire test furnace of

building elements in laboratory

Ying-Ji ChuangA1, Chin-Hsing HuangA1, Po-Hung ChenA2, Chieh-Hsin TangA1, Ching-Yuan LinA1

A1National Taiwan University of Science and Technology

A2National Taiwan University of Science and Technology and Kao-Yuan University

*Corresponding author:

Ying-Ji Chuang

E-mail address: [email protected]

Department of Architecture, National Taiwan University of Science and Technology, Taipei, Taiwan 10607 .

Tel: +886-2-27333141ext 7514; Fax: +886-2-27376721

Abstract

While installing a standard fire test furnace of building elements in a laboratory,

the planner should not only be concerned with ensuring sufficient room for

accommodation, but also with the safety of working personnel and the laboratory

itself which will be threatened by the thermal radiant heat from the furnace during

an uninsulation fire test. With the results of a standard fire test (test subject area of

3m3m) and some simple evaluation formulas, this research has analyzed the

relation between the distance and the thermal radiant heat under different fire test

times, which can be used as reference by laboratories planning to set up a furnace

and accompanying safety management. According to the study, there shall be no

combustible materials 5.6m in front of the furnace, and working personnel should

stay at least 14.1m away from the front side of the furnace to avoid damage to the

skin.

Key word: radiant heat, furnace, laboratory


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1. Introduction

Currently, standard fire test furnaces of building elements (furnace for short

hereafter), are commonly set in the laboratories of every developed country. In

Taiwan, about 10 furnaces have been installed in various private and governmental

organizations. These furnaces are the main equipment used to test the fire resistance

rating of various building elements. No matter in which country they are installed,

furnaces all have similar operational principles and construction. With ceramic fibers

or firebricks paved in its inner body, and running on gas or diesel oil, the furnace is

able to maintain its temperature within some specific standard time-temperature

curves[1-6]

, by which they are able to determine the fire resistance rating of the test

subject at the time the failure of its insulation, integrity or stability, occurs.

Generally speaking, the test subjects set in a furnace are large items (wall area:

at least 3m3m, height of columns: at least 3m, length of beams: at least 4m).A

laboratory needs to have large space to accommodate those facilities and test subjects.

Therefore, the hazards which could occur in construction sites or factories may also

take place in a fire test laboratory, for example, falling accidents from high altitude

and dangers imposed by overhead traveling cranes, fuel tanks, gas cylinders and so on.

In addition, regular processing machines and tools can be found in a fire test

laboratory. Hence there are certain standard operation procedures and regulations in

the fire test laboratory to prevent potential hazards, and the authorities in charge of the

laboratories will also conduct periodical and random inspections on the safety and

accuracy of the related test facilities, such as: computers, stopwatches, pressure

gauges, thermocouples, signal cables, gas tubes, gas tanks, fuel pipes, appearance of

the furnace, and the accuracy of its burning temperature. However the potential fire

hazards imposed on the laboratory by a running furnace have been constantly ignored;

therefore, incidents have occurred in Taiwan during which laboratory equipment and


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decorations were burned by the thermal radiant heat from furnaces.

The tests for furnaces can be categorized into two major types: closed type and

half-open type. Closed type tests are mainly used for beams and columns, which are

placed in a furnace with its cover closed. As the dangerous flames and thermal radiant

heat are isolated in the furnace, they are relatively safer than the half-open type tests.

The most hazardous situation takes place during the half-open type tests, in which the

thermal radiant heat is emitted from the front of the furnace. For instance, when a test

for a fire shutter with metallic blades of 1.5mm thickness (see Fig.1) is performed, the

exposed surface of the shutter is located inside the furnace, while the unexposed

surface extrudes out of it. As the furnace temperature rises, the thermal radiant heat

emitted from the unexposed surface fire shutter increases. Since the fire resistance

rating required by common rules on the fire shutter is at least one hour[7]

, so the

laboratory and the working personnel are exposed to the hazards inflicted by the

thermal radiant heat for at least one hour.

Nowadays, in every country the rules on furnaces have only specified the

related test capacities of the furnaces. None of them has defined the safety clearance

between the furnace and the surrounding facilities. With the absence of detailed

reference data, the location of furnace and the distance between the working

personnel and the running furnace are commonly determined by experience, or the

precedents of other laboratories. Therefore, the analysis of the potential hazardous

factors caused by furnaces is imperative. According to the observation results and test

data, this study estimates the dangerous zone caused by thermal radiant heat generated

during the half-open type test. The conclusions can be used as a valuable reference for

setting up a fire test laboratory and for laboratory authorities establishing relevant

rules in the future. The dimensions of the furnace (the area of the fire shutter tested is

3m3m) used in this research conforms to the ISO 3008, and since the test rules


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applied in countries around the world are identical or similar to the ISO 3008, this

study is not an isolated case; rather, the results can be applied to the laboratories of

other countries.

2. Furnace and specimen

The relation between the furnace temperature and burning time is shown in

Fig.2: 945.3during the first hour, 1049.0during the second hour, 1109.7during

the third hour, and 1152.8during the fourth hour. The inner surface of the furnace is

paved with ceramic fibers and firebricks, and the test subject is located at the fore part

of the furnace. For the test subject, such as fire walls, fire doors and fire shutters, the

area exposed to the fire is 3m3m. Because the insulation performance of fire walls

and fire doors is commonly demanded by most of the relevant rules, the tests for them

can be declared invalid and stopped in time to avoid imposing substantial hazards on

the laboratory when there is any flame penetrating the surface of the test subject, or if

the temperature of the unexposed surface exceeds the associated requirements (210

for any single point and 170 for the average)[1]

. But this is not the case for the test

of conventional fire shutters, which can only conform to the requirement of fire

integrity, but possess insufficient insulation performance. For instance, the

temperature of the fire shutters unexposed surface can reach 327~527 by the 30th

minute during a standard fire test[8]

, generating dangerous thermal radiant heat lasting

to the end of the test, since the flame is not able to penetrate the shutter blades which

are made of galvanized steel or stainless steel. As shown in Fig.4, the thermal radiant

heat at the location 1m away from the galvanized rolling shutter is 4.63w/cm2

the first

hour and 6.70w/cm2

the second hour. However, the corresponding data obtained from

a stainless steel rolling shutter are: 3.20w/cm2and 4.63w/cm

2,respectively, because of

lower emission rate[9-10]. Therefore the most dangerous situation facing the equipment

and working personnel of laboratories will occur during the testing of a galvanized


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rolling shutter.

3. Radiation

With the associated dimensionless factor and the temperature difference between

the fire shutter and a specific object[11]

, the thermal radiant heat absorbed by the object

can be calculated from Eq.(1). Howell[12]

recommended a simple formula, Eq.(2), to

evaluate the absorbed thermal radiant heat of the non-specified object. As shown in

Eq.(2), the thermal radiant heat from the fire shutter is associated with the view factor,

which becomes smaller as the distance between the object and the shutter increases.

The larger the distance is, the smaller the damage that will be caused by the thermal

radiant heat. Along the central axis of the fire shutter, the radiant heat and the view

factor are both larger than those at other positions. The view factor along the central

axis is expressed by Eq.(4).

)(44

oso TTq = Eq.(1)

1

sos

)11

(F

11)-

1(

++=oo

s

A

A

ssoo qFq = Eq.(2)

+

++

+

+= )

1(tan

1)

1(tan

12

1

2

1

22

1

2Y

X

Y

Y

X

Y

X

XFso

Eq.(3)

+++++=

)1

(tan1

)1

(tan12

14 2

1

22

1

2Y

X

Y

Y

X

Y

X

XFso Eq.(4)

: Stefan-Boltzmann constant (5.669610-8

Wm-2

K-1

)

: a dimensionless factor

sT : fire shutter surface temperature (K)

oT : object surface temperature (K)

soF : view factor (the fraction of radiant energy leaving the fire shutter surface


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which falls directly upon the object surface)

As : surface area of the fire shutter (m2)

oA : surface area of the Object (m2)

s : emissivity of the shutter surface

o : emissivity of the object surface

oq : thermal radiant heat flux of object (w/cm2)

sq : thermal radiant heat flux of fire shutter (w/cm2)

X= a/c

Y= b/c

a,b,c: as shown in Fig. 6

4. Result and discussion

The thermal radiant heat at the location 1m away from the shutter (made of

galvanized or stainless steel) can be found in Fig.3, so the thermal radiant heat of the

fire shutter can be calculated from Eq.(2) and Eq.(3). According to the

Stefan-Boltzmann Law, the thermal radiant heat is directly proportional to the fourth

power of the temperature. Therefore, for the shutter and the location 1m away from it,

the thermal radiant heat at the third and fourth hour can be derived by comparing the

furnace temperature and the thermal radiant heat at the location 1m away from the fire

shutter. As shown in Table 1, the thermal radiant heat for the galvanized fire shutter

can reach 11.92w/cm2 during the 4-hour standard fire test, and for the stainless steel

fire shutter, the thermal radiant heat during the first hour can also reach 4.39 w/cm2,

greatly exceeding thewoods ignition criteria of 1.0 w/cm2[12-15]

. These high thermal

radiant heat values can make working personnel uncomfortable or even cause second

degree burns to the skin. The study of Wieczorek et al.[16]

has pointed out that people

will not feel the pain in their skin, and can sustain an environment where the thermal

radiant heat is below 0.17 w/cm2. However, when the thermal radiant heat increases to


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0.2w/cm2 or 5w/cm2, they can only sustain 88 seconds or 0.58 second, respectively,

before getting second degree burns. Therefore, if the net space in front of the furnace

is too small, the working personnel can not avoid harm from the thermal radiant heat,

and the instruments and equipment before the furnace will also be damaged, and

eventually cause a fire in the laboratory. The hazardous distance (safety clearance) for

different standard fire resistance tests of fire shutters are shown in Fig.4 and Fig.5.

The safety clearance of 14.1m is necessary for a 4-hour fire resistance test of a

galvanized fire shutter, in order to reduce the thermal radiant heat to 0.17w/cm2, under

which working personnel can pass in front of the furnace safely without protective

equipment. In order to lower the thermal radiant heat to 1.0 w/cm2

and eventually

prevent a fire, a 5.6m safety clearance is necessary. Hence, this research recommends

that a 14.1m safety clearance in front of the furnace be arranged while installing a

furnace. Besides, for various tests, the thermal radiant heat values at different

locations in front of the furnace can be found in Fig.4 and Fig.5, which can be applied

in positioning the associated equipment for the safety management of the laboratory.

5. Conclusion

Normally, the time required for performing the standard fire resistance test will

be determined in advance, so the hazardous distance affected by the thermal radiant

heat can be accordingly defined from Fig.4~5. Therefore, the safety zone can be

arranged and eventually prevent the associated instruments and equipment from being

damaged. While installing a furnace in a laboratory, the planner should not only

consider the sufficient room and the accuracy of the associated facilities, but also the

possible hazards imposed by the thermal radiant heat from various test subjects.

According to the results of the 4-hour fire resistance test of a galvanized fire shutter,

the safety clearance should be at least 5.6m to avoid possible fire caused by the

thermal radiant heat and 14.1m to prevent personnels skin from being harmed. This


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study conclude that there should be 14.1m safety clearance maintained in front of the

furnace while installing a 3m3m furnace in a laboratory. If the size of the furnace is

bigger than 3m3m, the safety clearance should be expanded on the basis of the

evaluation with the simple formulas discussed above and the thermal radiant heat

value of the shutter. Through the study on the hazards imposed by the radiant heat

generated during a standard fire test, the study hope that the administration of

laboratories and the associated authorities will put greater emphasis on the safety

features and precautions in laboratories, to avoid any accidents from happening in the

future.

Acknowledgements

The authors would like to thank the TFPT Co., Ltd. for technically supporting this

research.

NOMENCLATURE

: Stefan-Boltzmann constant (5.669610-8

Wm-2

K-1

)

: a dimensionless factor

sT : fire shutter surface temperature (K)

oT : object surface temperature (K)

soF : view factor (the fraction of radiant energy leaving the fire shutter surface

which falls directly upon the object surface)

As : surface area of the fire shutter (m2)

oA : surface area of the Object (m2)

s : emissivity of the shutter surface


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o : emissivity of the object surface

oq : thermal radiant heat flux of object (w/cm2)

sq : thermal radiant heat flux of fire shutter (w/cm2)

X= a/c

Y= b/c

a,b,c: as shown in Fig.6

Reference

1. CNS 14803, Method of fire resistance test for rolling shutter of buildings [S](Taiwan), 2002.

2. ASTM E119, Standard Test Methods for Fire Tests of Building Construction andMaterials [S], 2000.

3. ISO 3008, Fire-resistance tests -- Door and shutter assemblies [S], 1997.4. JIS A 1304, Method of fire resistance test for structural parts of buildings [S]

(Janpan), 1999.

5. UL 263, Fire Tests of Building Construction and Materials [S], 1998.6. BS 476 Part 22, Fire Test of Building Materials and Structures. Methods for

determination of the fire resistance of non-loadbearing elements of construction

[S], 2002.

7. Taiwan building code [S], 2006.8. L.T. Wong, Safe distance of fire shutters in shopping malls [J], Architectural

science review, 2003, 6(4):403-409.

9. Love TJ. Radiative Heat Transfer [M]. Ohio, USA: Charles E. Merrill PublishingCompany, 1968.

10.L.T. Wong, Hazard of thermal radiation from a heated fire shutter surface to astanding person [J], Building service engineering and research and technology,


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2003, 24(1):1-8.

11.Galbraith GH, McLean RC, Stewart D., Occupational hot exposures: a review ofheat and mass transfer theory [J], Journal of Engineering in Medicine, 1989,

203(3):123-31.

12.Carlos J. Hilado and Regina M. Murphy, Ignition and flash-fire studies ofcellulosic materials [J], Fire and Materials, 1978, 2(4): 173-176.

13.Esko Mikkola and Indrek S. Wichman, On the thermal ignition of combustibles [J],Fire and Materials, 1989, 14(3):87-96.

14.Lin, C.Y., Study of exposure fire spread between buildings by radiation [J],Journal of Chinese Institute of Engineers, 2000, 23(4):493-504.

15.A. W. Moulen, S. J. Grubits, K.G. Martin and V. P. Dowling, The early behaviourof combustible wall lining materials [J], Fire and Materials, 1980, 4(4):165-172.

16.Wieczorek, C.J. and Dembsey, N.A., Human variability correction factors for usewith simplified engineering tools for predicting pain and second degree skin burns

[J], Journal of Fire Production Engineering Research and Technology, 2001,

24(1):1-8.


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Fig.1 Standard fire test of 3m3m fire shutter

0

200

400

600

800

1000

1200

0 20 40 60 80 100 120 140 160 180 200 220 240

Time (min)

Temperature()

ISO 834 standard

curve

Fig.2 ISO 834 standard temperature-time curve


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0

1

2

3

4

5

6

7

0 20 40 60 80 100 120

Time (min)

Radiantheatflux(w/cm^2)

stainless steel fire shutter

stainless steel fire shutter

Galvanized fire shutter


Fig.3 Radiant heat fluxes recorded at 1 m across from fire shutters

0123456789

10

1112

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Distance (m)

Radiantheatflux(w/cm^2) 1 hr fire test

2 hr fire test

3hr fire test

4 hr fire test

Fig.4 Thermal radiant heat flux between furnace and distance (galvanized fire shutter

test)


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012345678

9101112

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Distance (m)

Radiantheatflux(w/cm^2) 1 hr fire test

2 hr fire test

3hr fire test4 hr fire test

Fig.5 Thermal radiant heat flux between furnace and distance (stainless steel fire

shutter test)

dA1

A2

a

b

c

Fig.6 Geometry of the view factor


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Table 1 Thermal radiant heat flux of fire shutter

Test time

(hour)


(w/cm2)

Stainless steel fire shutter

(w/cm2)

1 m across

from fire

shutter

Radiation

source

1 m across from

fire shutter

Radiation

source

1 4.63 6.30 3.20 4.39

2 6.70 8.61 4.90 6.65

3 7.85 10.61 5.53 7.55

4 8.88 11.92 6.31 8.58

: calculated value

:measured value

consideration of safe distance of standard fire test furnace of building elements

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