Approved for public release by the

Director of the National Institute of

Standards and Technology (NIST)

on October 9, 2015.

NATIONAL BUREAU OF STANDARDS REPORT

7816

FIRE ENDURANCE OF STEEL

COATED WITH FIRE-RETARDANT PAINT

by

H. Shoub

and

E. W. Bdnder

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

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Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS REPORT

FIRE ENDURANCE OF STEEL

COATED WITH EIRE-RETARDANT PAINT

by

H. Shoub

and

E. W". Bender

Report to

Office of the Chief of Engineers

Bureau of Yards and Docks

Headquarters, U. S. Air Force

NATIONAL BUREAU OF STANDARDS REPORTS are usually preliminary or progress accounting documents intended

for use within the Government. Before material in the reports is formally published it is subjected to additional evaluation and review. For this reason, the publication, reprinting, reproduction, or open-literature listing of this Report, either in whole or in part, is not authorized unless permission is obtained in writing from the Office of the Director, National Bureau of Standards, Washington 25, D.C. Such permission is not needed, however, by the Government agency for which

the Report has been specifically prepared if that agency wishes to reproduce additional copies for its own use.

NBS PROJECT

IOOO- 12- 10^-0

1

March 6 , 1963

NBS REPORT

7816

IMPORTANT NOTICE

ILL DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

FIRE

- ENDURANCE OF STEEL COATED WTTH FTHE-RETARDANT PAINT

by

H. Shoub

and

E t W. Bender

ABSTRACT

Sheet steel specimens were coated with

three commercial fire-retardant paints to

determine to what extent such treatment would

increase the fire endurance of the metal.

Tests were made with specimens coated with

zinc chromate primer, and one test with

asphalt primer on the sheet. Two of the

paints were incompatible with the asphaltic

materials. The results of the tests indicated

that, while there were some differences in the

performance of the paints, no significant

increase in fire resistivity would accrue from

the use, of any of them.

1. Introduction

A series of tests was performed to determine if the fire

endurance capacity of otherwise unprotected structural steel

building members or sheet steel surfaces in buildings could

be increased to an acceptable level by the application of

simple (nonreinf orced) coatings of commercial f j.re-retardant

paints. If such were possible, comparatively low cost fire

protection could be provided for buildings constructed with

open steel framing members. These are often used in warehouses, hangars, storage sheds and others, many of large

size and involving a considerable investment in the building

and its contents. The results also would be applicable to

sheet metal structures and to metal cladding of wooden

elements of a building.
- 2 -

As' the cost of large-scale testing", such' a~s" of columns

or" floors', was considered' excessive in the preliminary stage

of the investigation, the tests were confined to an examination of the results obtainable with the paints applied' to

moderate-size sheets of metal. The original program outlined

for the work comprised several recommendations not subsequently performed. It was apparent as the work progressed

that these parts of the program would add little or nothing

to the data forming the basis of the conclusions. Such time

as had been allotted for the omitted tests was expended in

efforts to overcome difficulties arising in the preparations

for and conduct of the tests completed.

2. Description of Materials and Specimens

The test specimens consisted of 24-in. square steel

panels cut from hot-rolled sheet of 0.075 to 0.078 thickness

(14 ga) . Combinations of metal primers and fire-retardant

paints were applied to one side of the panels. Before

application of the paint, thermocouple wires- (No. 24 ga

chromel-alumel) were attached at the center of each panel

by swaging around the wires inserted in holes about 1 in.

apart in the metal. The junctions formed on the face of the

plate were filed flush with the surface. The thermocouple

leads were placed on the back or unpainted face.

To simulate actual conditions in construction, where

steel columns and beams may have zinc chromate or other

metallic primer, and steel joists a bitumen coating, 12 test

panels were given a single spray coat of commercial zinc

chromate yellow primer and another 12 panels were similarly

treated with an asphalt-base material.

Fire-retardant paints were chosen with the criteria that

they should have achieved an Underwriters ' Laboratories , Inc.

flame-spread rating of not more than 25 , and smoke developed

not to exceed 50 (with the paints applied to Douglas fir

compared to uncoated red oak rated 100) . For practical purposes, a requirement that the paints be listed as scrubbable

was also established. Three paints, designated A, B, or C

in this report, were found to meet the requirements. All

three could be applied by brush in a single coat at a rate of

150 to 175 ft^/gal, the coverage recommended by the manufacturers, while the specimen was horizontal. Two of the paints

were reported as scrubbable as applied in a single coat; one

was reported as requiring the use of a thin overcoating to

achieve some degree of resistance to wet abrasion.
- 3 - In preparing the test specimens, an initial drying time

of 48 hrs was allotted to the prime coats. This was usually

adequate for the zinc chromate although in some cases- puckering and blistering occurred when the fire-retardant coating

was applied. It was possible, however, to prepare satisfactory samples with each of the three paints. Care was taken

to apply the paint evenly at the specified rate. The sheets

so treated were dried under ordinary interior ambient conditions for a minimum of 30 hays before testing.

Considerable difficulty was encountered with the bitumen

primer. While paint C could be applied with reasonably good

coverage over the asphalt-base undercoat, the solvents present

in the other two paints proved to be entirely incompatible

with the use of the primer. The volatiles in the fire-retardant

materials very quickly acted on the asphaltic paint to form a

soft and sometimes running conglomeration of the coatings.

Longer curing of the primer, up to 1 week, was tried in an

effort to secure a stable base for the fire-retardant paints.

The effect, however, was the same, and the effort was abandoned

as the use of further drying time was considered both impractical and not likely to lead to a different result. Two samples

of the effect of applying fire-retardant paints over bitumen

are shown in Fig. 1.

In the absence of specific instructions on the manufacturer^

label, the samples requiring a finish coat to impart the desired

washable quality were allowed to dry 2 days before being so

treated. Additional specimens were prepared by application of

the materials not compatible with asphalt primers, paint A and

B, over bare metal sheets at the recommended rates of coverage.

For purposes of comparison, some of the sheets were also prepared for test with coverings of zinc-chromate or asphaltic

primers only. With no rate specified in the instructions,

these were applied to give complete coverage as evenly as

possible over one side of the specimens.

3« Test Method and Equipment

The tests were conducted in a small furnace having a top

opening 23 - 3/8 in. square. This opening is closed by the test

specimen, which is thus exposed, on its underside to the heat

supplied by six gas burners in the furnace. Temperatures in

the furnace are determined from four thermocouples distributed

within the chamber. The average temperature is automatically

controlled to conform as closely as possible to the ASTM

Standard Time-Temperature Curve for Fire Tests of Building

Construction and Materials (ASTM E119-61)

.
The steel specimens were placed horizontally over the

furnace opening with the paint-protected side forming the

fire-exposed surface. The unexposed surface was heavily

insulated in an effort to simulate the most severe condition

of possible exposure, which would approach the state of bar

joists or columns in a surrounding fire. This was accomplished

by placing a frame of 4-in. steel channel stock, 26 in. square

on the inside, over each specimen under test, and filling the

square with 3~in - of perlite. As a check on the insulating

effect, five thermocouples were placed in the perlite at

different distances above the thermocouple at the center of

the test specimen.

The response of the thermocouples, those in the furnace

as well as the one in the specimen and those in the insulating

layer, was recorded at 1-min intervals with automatic equipment.

The test exposures were continued somewhat beyond the time

required to attain a temperature of 538°C (1000°F) on the

steel, which was taken as the criterion of failure in these

tests

»

4. Results of Tests

The several combinations of paints used are shown in

Table 1 together with the results of the tests. There appear

to be some small differences in the effectiveness of the three

fire-retardant paints. In addition to showing the times at

which failure occurred (col. II), an attempt is made in the

table to demonstrate differences existing in the paints by

indicating the average of the furnace temperatures at the time

of failure (col. III). It should be noted that where the

protection afforded the steel sheet is small or nonexistent,

it is quite possible that the lag in the furnace thermocouples,

which are encased in iron pipe, will be greater than that of

the thermocouple attached to the specimen.

Columns IV and V of the table show the average furnace

temperatures at 5 min (nominally 538°C or 1000°F) and the

temperatures in the steel at the same time. To indicate the

degree of exposure and compensate for any departures from

normal in the temperatures in the furnace, the sum of steel

temperatures in each test, taken each minute and including

the whole minute immediately following failure are related to

the similarly observed average furnace temperatures for the

same time interval (col, VI-VIII)

.
- 5 -

It can be seen from the table that paint B applied to

bare metal had the longest endurance (Test 1) followed by

paint C over zinc chromate (Test 3 ) and paint B over zinc

chromate (Test 4) . A very rapid rise in temperature

occurred in the sheet treated with asphalt primer only (Test 6),

and this was but little improved by additional coating with

paint C (Test 7) • Specimens coated with paint A had the- same

endurance whether prime coated with zinc chromate or not

(Tests 8 and 2) ; however, the exposure was somewhat greater

in the test without the primer, as can be seen in the steelto-furnace temperature ratios. It would appear that the use

of a primer tends to reduce the fire endurance imparted by

the paint, possibly because the primer itself contributes heat

to the exposure. A point to remember in comparing the ratios

of col. VIII is that the lag in the response of the pipeencased furnace thermocouples may contribute greatly to the

differences in temperature which determine the ratios.

Although the fire tests were made under conditions

approaching those of greatest severity, as indicated by a

high temperature gradient through the perlite insulating layer

(Table 2) , the increments of fire resistivity resulting from

the use of the paints were so small as to be of practically

no significance. The test specimens were prepared with care,

and only those appearing to have the best coverage were used.

The results of the tests, falling far below any acceptable

standard of protection, serve as an indication of the ineffectiveness of applying simple fire-retardant coatings to metallic

building elements or structures. The test program, it should

be noted, was for the purpose of determining what insulating

effect, if any, the paints may have, and was not an examination

of their flame-spread properties, nor was any correlation

observed between the results of these tests and the UL flamespread ratings.

5. Summary and Conclusion

Three commercially available fire-retardant paints were

applied to sheet steel specimens to determine if by such

means the fire endurance of steel could be materially increased.

The paints were applied over zinc chromate primer, and one was

used with an asphalt-base undercoat. Two of the paints were

found to be incompatible with the asphaltic material, and tests

were made with these paints applied over bare metal.
- 6 -

The tests were conducted in a small furnace regulated

to follow approximately the standard ASTM time -temperature

curve for tests of building materials and constructions. To

secure as severe conditions as posssible, the unexposed’ side

of the specimens was heavily insulated to prevent heat loss.

Although the paints were carefully applied, following

the manufacturers' instructions, the gain in heat resistivity

of the steel sheets was at best insignificant, and far below

that required for a meaningful fire endurance rating. There

appeared to be some small differences in the effectiveness

of the several paints. Application over primers tended to

give lower increases in endurance than when used on bare

metal, with the asphalt primer having a greater deleterious

effect than the zinc chromate. The tests were not an investiation of the flame-spread properties of the material, and no

correlation was noted between the results and the flame-spread

classifications listed by the Underwriters' Laboratories, Inc.
Table

1.

Results

of

Tests

i—

i

i—M

>

i—

i

o >

•H

-P I—

I

0 l—

I

tr; >

i—i i • i—

I

p a 0

> W)P CD

a> e p P w

0

o

I • CO

• d d

I—I W)vH d

> 0 S d

p P

>

-p0 •

i—i a

0 • *H 0 ft g o

-PS o 0 0lT\

&H

>M

a -p d 0 • d d P • *H

P B o

• S o

bo 0 Un

> EH

<aj

P

I—

I

I—

I

d p

d 0 0

d d

P • d

p p

• £ *H M0 0

EH p

<u

O

o

O 0^~s O

-P d O 0

d o 0

0 Pcx) • • E 'H X d

•H 0 tT\ •H EH P w B

HH

i—

I

0

•Hd

0P

0S

d

B

d

i—

I

o

o

-p . 0 o

0 p

Eh

CM ITS r—

1

CM r—

1

in- 00 O'- 00 Q O O IfN 00 pf CM

• • • • • • • • o 1—

1

( 1

l 1 P p 1—1 r—

1

OO Jr vO CM ON 00 CO CM vO CM 00 vO O'- ON OO l>- CM on pf EN- CP CM OO O

oo CM oo CM 1—1 r““

1

r—

|

CM

CM vO O pf CM CO OO CM vO r—

1

PT 1 1 ON CO OO i—

l

ON C\J pf 1—1 VO CM vO

rO CM on CM 1—1

1

1 i—

1

o EN- N- OO 00 IfN r—

1

OO

vO IN- ON vO I—1 IfN \o 00 oo IfN PT PT vO VO vO IfN

<—

1

on CM O- O O'. OO IfN 0s- 00 OO 1—

1

PT on OO i—

1

PT IfN IfN IfN IfN IfN IfN IfN

o PT p O 00 CM vO CO

c^ pf ON o CM vO O VO

vO IfN IfN vO PT CO PT pf

o O o O IfN O o O

IfN oo on oo pf lr\ OO OO

00 pf ep vO on CM OO pf

d

z' s 0

0 0 0 >> >> B 0

p p P P r—

1

•H P

d d 0 0 0 d d d 0

PQ 0 <3\ 0 o s PQ B B o P o O P < B

e B o o o r—

1

O

-P P -P P P T3 d PT) d d d 0 d P0P PT)

d d d d d d -d d d -d -d 0 -d 0 - d d p d d .d

•H P •H P •H 0 O P 0 o o P B •H 0 0 •H 0 o

0 0 0 0 •H 0 P 0 .-d 0 P O P O p d p d d d < d p p p d

d d IS] ISl tS3 P P 0 ISI 0

1—

1

CM oo PT IfN vO 00
Table 2, Temperatures in Perlite Insulating La;ver

Temp * Test Time of of Temperatures in Perlite

No. Observation Steel Distances above Steel Specimens

8/8 in. 8 A- in* 1

- 1/2 in. 2-1/5- in. 2-5/8 in.

min. °C °C °C °C °C °C

1 9 54-7 266 162 62 37 32

2 5 577 238 81 5-9 32 30

3 8 587 330 193 63 4-5 38

4 7 569 309 173 71 5-2 37

5

9- 54-9 212 105 - 33 36

6 3 54-8 209 75 5-1 35 32

7

5- 566 209 96 5-6 35 33

8 5 583 295 156 30 26 32
Fig.

1.

Fire

retardant

paint

applied

over

bitumen

primer.

The following paints were used in the tests described in

National Bureau of Standards' Report 7816:

Zinc chromate yellow primer and asphalt base primer,

both "Paint Pot Products" manufactured by Jerry

Bachman, Inc., Washington, D. C.

Paint A, Albi~107A, Albi Manufacturing Co., Rockville,

Connecticut; one coat, no primer or overcoat; density

10,79 lb/gal; UL ratings on Douglas fir (Basis, uncoated

red oak 100), flame spread 20, fuel contributed- 20-25,

smoke developed 0-5.

Paint B, Ocean No. 900, Ocean Chemicals, Inc., Niagara

Falls, N. Y. ; one coat, no primer or overcoat; density

10.71 lb/gal; UL ratings, flame spread 25, fuel contributed 25 , smoke developed 45-

Paint C, Saf 383? Alim Corporation, New York; resin base

two component paint; one coat, no primer or overcpat

(following overcoat required for washable finish)

;

density 11.76 lb/gal; nonflammable solvent; UL ratings,

flame spread 15, fuel contributed 15, smoke developed 5*

. Saf 202, Alim Corporation; overcoat for Saf 303? -coverag

500 ft 2/gal** density 11. 90 lb/gal; UL ratings (over Saf

3 O3 ) , flame spread 10, fuel contributed 15, smoke

developed 0.

i;. S. DEPAHTMENT OF COMMERCE

Luther H. Hodges, Secretary

NATIONAL BUREAU OF STANDARDS

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

The scope of activities of the National Bureau of Standards at its major laboratories in Washington, D.C., f&ad Boulder, Colorado, is suggested in the following listing of the divisions and sections engaged in technical work.

In general, each section carries out specialized research, development, and engineering m the field indicated by

its title. A brief description of the activities, and of the resultant publications, appears on the inside of the

front cover. WASHINGTON, 0. C.

Electricity. Resistance and Reactance. Electrochemistry. Electrical Instruments. Magnetic Measurements,

Dielectrics. High Voltage.

Metrology. Photometry and Colorimetry. Refractometry. Photographic Research. Length. Engineering Metrology.

Mass and Scale. Volumetry and Densimetry.

Heat. Temperature Physics. Heat Measurements. Cryogenic Physics. Equation of State. Statistical Physics.

Radiation Physics. X-ray. Radioactivity. Radiation Theory. High Energy Radiation. Radiological Equipment.

Nucleonic Instrumentation. Neutron Physics.

Analytical and Inorganic Chemistry. Pure Substances. Spectrochemistry. Solution Chemistry. Standard Refer- ence Materials. Applied Analytical Research. Crystal Chemistry,

Mechanics. Sound. Pressure and Vacuum. Fluid Mechanics. Engineering Mechanics. Rheology. Combustion

Controls.

Polymers. Macromolecules: Synthesis and Structure. Polymer Chemistry. Polymer Physics. Polymer Characterization. Polymer Evaluation and Testing. Applied Polymer Standardsand Research. Dental Research.

Metallurgy. Engineering Metallurgy. Microscopy and Diffraction. Metal Reactions. Metal Physics. Electrolysis

and Metal Deposition.

Inorganic Solids. Engineering Ceramics. Class. ;o»id State Chemistry- Crystal Growth. Physical Properties.

Crystallography.

Building Research. Structural Engineering. Fire Research. Mechanical Systems. Organic Building Materi&ie.

Codesand Safety Standards. Heat Transfer. Inorganic Building Materials. Metallic Building Materials.

Applied Mathematics. Numerical Analysis. Computation. Statistical Engineering. Mathematical Physics. Operations Research.

Data frocessing Systems. Components and Techniques. Computer Technology. Measurements Automation.

Engineering Applications. Systems Analysis.

Atomic Physics. Spectroscopy. Infrared Spectroscopy. Far Ultraviolet Physics. Solid State Physics. Electron

Physics. Atomic Physics. Plasma Spectroscopy.

Instrumentation. Engineering Electronics. Electron Devices. Electronic Instrumentation. Mechanical Instru- ments. Basic Instrumentation.

Physical Chemistry. Thermochemistry. Surface Chemistry. Organic Chemistry. Molecular Spectroscopy. Elementary Processes. Mass Spectrometry. Photochemistry and Radiation Chemistry.

Office of Weights and Measures. BOULDER, COLO.

Cryogenic Engineering Laboratory. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Cryogenic Technical Services.

CENTRAL RADIO PROPAGATION LABORATORY

Ionosphere Research and Propagation. Low Frequency and Very Low Frequency Research. Ionosphere Research. Prediction Services. Sun-Earth Relationships. Field Engineering. Radio Warning Services. Vertical

Soundings Research.

Radio Propagation Engineering. Data Reduction Instrumentation. Radio Noise. Tropospheric Measurements.

Tropospheric Analysis. Propagation-Terrain Effects. Radio-Meteorology. Lower Atmosphere Physics.

Radio Systems. Applied Electromagnetic Theory. High Frequency and Very High Frequency Research. Fre- quency Utilization. Modulation Research. Antenna Research. Radiodetermination.

Upper Atmosphere and Space Physics. Upper Atmosphere and Plasma Physics. High Latitude Ionosphere

Physics. Ionosphere and Exosphere Scatter. Airglow and Aurora. Ionospheric Radio Astronomy.

RADIO STANDARDS LABORATORY

Radio Physics. Radio Broadcast Service. Radio and Microwave Materials. Atomic Frequency and Time-Interval

Standards. Radio Plasma. Millimeter-Wave Research.

Circuit Standards. High Frequency F^lectrical Standards. High Frequency Calibration Services. High Frequency

Impedance Standards. Microwave Calibration Services. Microwave Circuit Standards. Low Frequency Calibration

Services.

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