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Approved for public release by the

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Standards and Technology (NIST) on October 9, 2015.

OF STANDARDS REPORT

\ '6530

TRANSLATION

by

Bernard. H. Fouquet

of paper in french

wiTm-TODS ADOPTED IN THE U»S»S»R»

FOR THE STUDY OF FIRE RESISTANCE OF BUILMNG

ELEMENTS AND SOME OF THE RESULTS OBTAINE

by

V, I. Mourachev

Active member of the Academy

Architecture of the U.S.S.R.,

and Professor.

of Building and

Doctor in Science

<^BS>

«. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
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NATIONAL BUREAU OF STANDARDS REPORT

NBS PROJECT NBS REPORT

1002-12-10120 September 1, 1959 6530

TRANSLATION

by

Bernard H. Fouquet

of paper in french

METHODS ADOPTED IN THE U.S.S.R.

FOR THE STUDY OF FIRE RESISTANCE OF BUILDING

ELEMENTS AND SOME OF THE RESULTS OBTAINED

by

V. I, Mourachev

Active member of the Academy of Building and

Architecture of the U.S.S.R., Doctor in Science

and Professor.

IMPORTANT NOTICE

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

intended for use yvithin 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.

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

Original : presented in

French by

M. Mourachev

METHODS ADOPTED IN THE U.S.S>R . FOR THE STUDY OF FIRE RESISTANCE OF BUILDING

ELEMENTS AND SOME OF THE RESULTS OBTAINED

by

V. I. MOURACHEV

Active member of the Academy of Building and

Architecture of the U.S.S.R.^ Doctor in Science

and Professor.

1. General principles on the evaluation of fire resistance.

The elaboration of a method for the correct evaluation of

the fire resistance of structural elements, particularly

elements in reinforced concrete, has acquired a considerable

importance

,

There are two contributing factors:

First, reinforced concrete occupies a preponderant situation

in buildings; second, structures of reinforced concrete are extremely varied. The use of thin-walled elements, the utilization

of metals of high elastic limit and in particular prestressed

cold-drawn steel wires HR, have a marked Influence on the technical properties of the construction, fire resistance included.

The answer to questions relative to fire resistance of

elements used in structures, and of entire buildings, cannot

be based only on trials of these elements and buildings. The

intensity of the entire fire must be studied.

The notion of the limit of resistance to fire which is

measured in hours and that of the theoretical duration of the

fire also expressed in hours must be defined. These two values

are related by a coefficient that we shall call the index of

fire resistance. It is in multiplying the theoretical duration

of the fire by this index that we obtain the value of the limit

of resistance to fire required. The real value of the resistance

of an element cannot be less than the required value. One thus

obtains the expression'* used for the computation of the fire

resistance:

R^ KqD (1)

where

Rp is the res-l limit of resistance to fire of an element expressed

in hours.

* Vo I, Maurochev. Resistance of structural elements to thermal

exposures

.

- 2 -

D is the theoretical duration of the fire.

Kq is the index of fire resistance.

The performance requirements to which the elements are

subjected are a function of the fire duration ”D", the latter

depending on the type and on the quantity of combustible

materials and on its physical state, form and dimensions of

the rooms as well as the presence of automatic extinction

equipment and other factors.

Relationship (l) makes possible the standardization of

the limit of fire resistance of the elements of construction

for a given duration of fire by Introducing standardized

values for the index of resistance.

The value of this index for the entire building is chosen

according to the degree of non-combustibility desired, that

is to say, according to its behavior required during and after

the fire. With regard to the different elements, the choice

of values for the indices is determined by their relative

importance and by the importance of the equipment and its

various positions in the building, etc.

The value of Kq can be below or above unity in accordance

to the degree of the resistance to fire required of the building and of its various parts and elements.

In this manner relationship (l) furnishes the necessary

data in the computation of the fire resistance of the buildings

and other structures.

The experimental and theoretical research undertaken at

the Central Institute of Fire Fighting under the direction of

the author is based on the fundamental considerations given

above. These considerations, however insufficient they may

be, form the basis for the Soviet standard related to fire

fighting. (standard 102-5^4)

Present research is directed to studying the limit of

resistance to fire of building elements as well as defining

more precisely this theory in Itself. On the other hand this

research covers also the Intensity of the fire D as a function

of the different types of combustibles and the varied corjdltlons

of their combustion.

-3-

The intensity of a fire is characterized by its auration

and by the temperature developed during the fire. During

the combustion of wood and other similar materials (paper, cloth

etc.) the temperature-time curve of a fire goes through three

general well defined phases (fig. 1)

Phase 1 - period of ignition during which the temperature

in the module rises in undefined fashion.

Phase II - period of Intense combustion with rapid rise

in temperature until maximum is obtained.

Phase III- period of extinction of the fire with a drop in

temperature at first rapid and then considerably

slower

.

It would be rather inconvenient to use these curves in an

experimental determination of fire resistance of buildings as

well as for the evaluation of the duration of the fire.

For this reason, a standard time temperature curve of a

theoretical fire (fig. 2) has been adopted which closely

resembles the standard time- temperature curves adopted by

other countries.

In Fig. 2 we have Included the standard curve with time

temperature curves for real fires obtained by burning 25, 50,

100 and 150 kg. of wood to a square meter of floor of a module.

The parts of these curves related to the Ignition period which

have no influence on the rise in temperature of the building

have been omitted. The conversion of the duration of a real

fire to the duration of a standard fire is performed in the

following manner: For the duration of the theoretical fire

the time for which the area under the standard curve equals

the corresponding area under the real curve has been adopted;

(see fig. 3) this duration is plotted along the abscissa and

is expressed in hours.

It can be seen that the rise in temperature of the surrounding walls in fires that follow the standard curve differ

very slightly from the rise in temperature produced during a real fire.

In obtaining the conversion, the ignition period is neglected,

and for the terminations of the real fire we chose from the

time temperature curve of the latter the point at which the real

heating begins to express a slower rate than the theoretical

heating. Experiments conducted at the Institute show that this

takes place when the temperature of the real fire lowers to

600° to 400°, fig. 3.

-4-

In taking this data as a basis, it can be determined with

enough precision that the duration of the theoretical fire

in a residential building can be obtained in the following

manner (assuming the absence of all extinguishers)

D = T q = 0.02 q (2)

200,000

where: T is the specific heat of wood and similar materials

equal, on the average, to 4,000 Kcal/kg

q is average quantity of combustibles in kg per

square meter of floor space.

200,000 is the conventional quantity of heat in

Kcal emitted in one hr per square meter of an

area.

In the most general case, the presence of various liquid

and solid combustibles in the room, the expression representing the theoretical duration of the fire is given in the

following form:

D = f (q, o) (3)

Where

q is the average quantity of each type of combustible

in kg of square meter of floor

T is specific heat in Kcal/kg

(3 is the coefficient of combustion of each material

which depends on its proximity to the fire.

C is the conventional quantity of heat in Kcal

emitted in one hour and per square meter of

floor space.

V is the factor taking into account the shape, the

dimensions, and the degree of ventilation of the

considered space.

c::^ is the factor taking into account the influence

of the active extinguishing methods taken to put

out the fire, such as: automatic equipment, firemen in the vicinity and access to the building.
V

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- 5

-

The real limiting resistance of the structure is determined experimentally under a thermal system analagous to that

of the theoretical fire (standard). For a number of elements

the Institute has evaluated methods permitting the determination of this limiting resistance by means of computations.

Whatever may be the case a precise definition of the terms

must be found for the limiting resistance to fire of constructions as a function of the services that they may furnish

ordinarily and in times of fire and one must enumerate the

circumstances denoting that this limit has been attained.

It is generally conceded that the limiting resistance

which is expressed in hours is exceeded when the element in

question ceases to be fire retardant or loses its quality

of mechanical strength during and after the fire. Up to

then the signs characterizing the limit mentioned are the

following

;

1) The appearances of breaks through which flames can

pass into the adjoining room and can then start a fire;

2) The rise in temperature on the cold side of a wall

above the maximum temperature on the cold side of a

wall above the maximum temperature established by

standards

;

3 ) Loss of the supporting power of the element.

The two first signs mentioned are sufficiently clear and

are of Importance only during the actual fire.

The third sign requires to be studied more thoroughly,

the supporting power of an element being of extreme importance not only during the fire but after.

2. Behavior of building elements during a fire and criterion

of the limiting state of its supporting power . In modern buildings it has been demonstrated in experiments

at the Institute that resistance differs according to the

action of a fire. It follows that a precise definition

universally adopted for the limiting state of a building

element's supporting strength acquires great importance.
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- 6 -

The criterion of complete destruction (collapse) of an

element cannot be adopted because it does not take into

account its state preceding the immediate failure and in

particular the Irreversible changes and the loss of the

supporting strength. This quality is of extreme importance

for old buildings computed with Kq greater than 1, that is,

when the supporting strength and the rigidity must be

retained during and after the fire.

In other termSj, if we adopted the criterion of total

destruction (collapse), the structural elements developed

differently but possessing the same limiting resistance to

fire and having been submitted to the same type of fire

would not retain the same supporting strength and would not

guarantee the same security during and after the fire. The

time elapsed to total destruction is significant only for

elements calculated with Kq smaller than 1, that is to say,

for those which must only stand a certain number of hours during

the fire without being of any importance after the end of the

fire

.

Consequently, we shall adopt as the criterion of limiting

fire resistance, with regard to supporting strength and

rigidity of an element, the Increase in irreversible changes

to the point where they become unusable.

In order to explain the principles given above, we will

use the results of the experimental studies of fire resistance

of elements in, reinforced concrete (mild steel) and prestressed

concrete, (steel wire HR cold-drawn.)

In our experiments, the destruction of these two types of

elements by the action of fire started by the formation of a

plastic failure (points 0 on fig. 4), that is to say, when

because of the rise in temperature the limit of the elasticity

of the mild steel and the resistance of the steel wires HR

decreases to the value of the forces exerted during the normal

burning. At that time there are observed the opening of large

breaks in the zone of stress and a rapid Increase in the deformation. In fig. 4 there are reported the values for total

changes of each element composed of deflections caused by the

variation in temperatures in the section of those elements,

(reversible changes) and supplementary deflections caused by

the modification of the physical and mechanical properties

of the concrete and the steels by the action of the heat.

This last deformation is irreversible and Influences considerably the evaluation of limiting resistance to fire. With

regard to supporting strength, since the larger residual deformations always occur simultaneously with a loss of supporting

strength, such deformations signify that the limit of supporting

has been reached.

- 7

-

In order to compute this residual deformation, experiments

were undertaken during which the rise in temperatures of the

elements were stopped slightly before the formation of the

plastic failure. After the flames were extinguished, the

elements still under load were left to cool slowly at the

same rate as the oven. The experiments were conducted on

the reinforced concretes with mild steel and steel wire HR

prestressed.

The curve 1 of the fig. 5 represents the increase in total

deflection of one of the four beams tested, reinforced with

mild steel (steel No. 3 ) on which the heating was conducted

for 49 minutes and stopped three minutes before the point of

the plastic failure. The decrease in deflections is illustrated

by the curve No. 2 which is parallel to curve No, 3j the latter

represents the deformation due only to heat. If curve No. 2

is displaced to point "a" it will coincide practically with

curve 3.

The difference between the total deflections and the

changes due to heat alone furnishes the value of the residual

deflections under load due to the modifications of the physical

and mechanical properties of the materials caused by heat.

These modifications are explained by the hot flow of the metal

and of the concrete and by a change in the elastic properties

of the concrete.

In examining the curves represented in fig. 5 it is seen

that for an element reinforced with ordinary steel, the

irreversible changes constitute only a small percentage of

the total deflections up to the point where the plastic

failure occurs.

Consequently, we cannot adopt as limiting resistance with

regard to supporting strength of the elements in reinforced

concrete with mild steel, the time corresponding to the formation of the plastic failure (point 0) which Immediately

precedes the total collapse.

The curves represented in fig. 6 furnish a completely

different picture. In this figure we have plotted the total

changes and the reversible deformations of three panels reinforced with .preetressed wires of ultimate strength of

18,000 kg/cm^,* the first wall being heated to 313° (42 min.),

the second panel to 315° (36 min.) and the third panel to 375°

(45 min.), after which the three panels were cooled slowly

under load.

* 1 kg/cm2 = i4.22 Ib/in.^ (added in translation)

- 8 -

It can be judged from these curves that the irreversible

change of the elements reinforced with prestressed steel wires

HR (difference between curves 1 and 2; 3) constitute approximately 60^ of the total changes and are developed as soon as

the heating of the metal occurs.

The beginning of the residual deflections are explained by

the hot flow of the metal submitted to very high stresses.

This reasoning is confirmed by preliminary experiments conducted

at the Institute on the hot flow of steel wire HR of 15,000

kg/cm"^ and heated to 300°, with subsequent cooling. Even at

200° the flow becomes very apparent and attains a considerable

value at a temperature of 300°. The rate of heating of the

wires is similar to the heating of the reinforcements in panels

1 and 2, After complete cooling the residual deformation due

to flow, per unit length, was equal to ,0038. Also the similar

deformation leads to a complete loss of pretension and to the

formation of Important irreversible changes of deflection. In

effect, for the ribbed panels which have been used in the

experiment described above, an elongation of the steel equal

to .0038 would result in a deflection amounting to 1^ of the

span.

Experiments conducted on the elements reinforced with

Steel of ultimate strength equal to 16,000 kg/cm^ have confirmed

these conclusions. The heating of steel to 300° resulted in a

total loss of pretension and in a reduction of rigidity to less

than 1/3 of the Initial rigidity.

Prestressed beams, after heating and cooling., behaved

under load in the same manner as non-prestressed beams.

Upon heating of the reinforcements to 220° a loss of pretension equal to 50 to 55^ and a loss in rigidity of the beams

equal to 1/2 resulted.

As has already been said, one indication of the limit to

fire resistance in these elements is the formation of undue

residual deflections. In fig, 7 we have then the curves of

Irreversible changes on the elements tested as well as the

temperature of their reinforcements.

-9-

It can be noted that the residual deformations of the beams

reinforced with mild steel (curve A) increase in time proportionately to the heating of the metal to the point of

deformation of the plastic failure^ that is to say to the

time when, under the heat, the limit of elasticity of the

steel falls to a value equal to the existing stresses.

In the case considered the steel had elastic limit of

2,340 kg/cm^ which decreased to 1,460 kg/cm^ (value equal

to the working stress) at a temperature of 460°. At that

time the residual deflection was only of the span,

It can then be seen that the protection of this type of

construction during and after the fire can be assured, if

that is required by the existing standards, by adopting as

an index of fire resistance the values of 1,1 to 1.2. In

this case the residual deflections cannot be any higher than

230 ~~^Eo total span and the supporting strength

of these elements after the fire would be reestablished

completely because after cooling the soft steel regainsall of its mechanical resistance. After the fire, minor

repairs on the lower surface of the elements will be

sufficient

.

However, the deformations of the elements reinforced with

prestressed wires of HR steel curve 1, 2 and 3 of fig, 7 will

reach, at the time of the plastic failure, (450° in our case)

the much higher values of 1/50 to l/40 of the span. This

signifies that the elements become unusable for other reasons

much before the limit of resistance of the steel has reached

the existing stresses.

As we have indicated previously this comes from the loss

of pretension and of the hot flow of the metal. It follows

that for the prestressed concrete the elapsed time before

the appearance of the plastic failure cannot be adopted as

a measure of the limiting resistance to fire because this

does not guarantee the salvaging of the elements in question

after the fire if this is required by the standards.

However, for buildings of the third and fourth categories

of non-combustibility (Soviet standard) for which the salvaging

of the elements after a fire is not required, only the time

of heating before complete destruction is important in the

evaluation of the fire resistance of those elements.

- 10 -

It can be seen then that the appearance of irreversible

changes is a sign which indicates that the limiting resistance

has been attained, Hovrever^ there are other factors 'which

must equally be taken into consideration. Thus the limitation

of residual deflections can guarantee security only for the

buildings which after cooling regain their supporting strength

and their rigidity. We have already shown that this is the

case for concrete reinforced with ordinary mild steel.

For concrete reinforced with steel wire HRj the element

will regain its initial supporting power only if the maximum

temperature obtained during the fire is not sufficient to provoke

the irreversible loss of strength due to cold working.

Experiments indicate that for steel of 18,000-20;, 000

kg/cm such a loss of strength becomes noticeable at 200*^.

Fig, 8 shows clearly that this loss is a function not only

of the relative value of the increase in strength obtained

by cold working but also of the thermal exposure,

A rise in temperature to 800° produces in the steel a complete

loss of resistance and reduces it to its primitive state.

Thus the loss in supporting strength constitutes the second

factor which shows that the limiting resistance has been

obtained.

Also, the irreversible loss of rigidity indicates that the

element has reached its limiting resistance. For reinforced

concrete such a loss comes from the lowering of modulus of the

concrete after heating, from a partial loss of the bond between

the concrete and the steel, and in the case of prestressed

concrete, in the loss of pre-tension.

Actually, the standards in existence in the U,S«S,R. relative

to structures made with reinforced concrete take into consideration that the limit of resistance of an element is attained in

the following cases:

1, The Irreversible changes (residual deflection),

allowance being made for an initial working

deflection, reaches 0,01 of the free span,

2, An Irreversible loss of supporting power of 10^.

3 , An irreversible loss of rigid strength of 20^,
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- 11 -

Flg. 7 shows that prestressed elements reinforced with

wires of HR steel of 18,000 kg/cm"^ reach a residual deflection

equal to 0.01 of the span when the metal is heated to 200-300°,

At 200° we observe an Irreversible loss in rigidity and in the

resistance of the steel. (see Fig. 8)

It Is evident that the admissible temperature to which HR

steel can be subjected depends on the relative value of the

supplementary resistance obtained when the wire is cold-drawn.

But the experimental data relative to elements reinforced

with steel, the resistance of which is below 15,000 kg/cm^_,

is still lacking.

Analysis of data furnished in fig. 7 indicates that at

the thickness equal to the protective thickness when the rate

of heating of the metal is the same, the limit of resistance

to fire of the supported elements reinforced with mild steel

is at least twice that of the elements reinforced with steel

wires HR of 15,000 to 18,000 kg/cm^. That is the reason the

standards (Standard 102-54) require, for the element reinforced

with wires HR, corresponding increase in the thickness of the

cover.

The experiments conducted at the Institute show also that

the limiting resistance of the elements Incased in supports

(or in the presence of adequate restraint) Increases considerably if the relation between the sections of steel at

the supports and in the span is not less than 2* The. time

elapsed before collapse Increases in the ratio of 1 to 3 (see

curve 3 of fig, 4) because of redistribution of stresses which

are produced during the heating making it possible to achieve

a temperature of 800 - 900 ° in the longitudinal reinforcement.

As for elements reinforced with steel wires HR of 15,000-

18,000 kg/cm'^ the limiting resistance is not influenced by

an Incasement or by the presence of a restraint because the

heating of the metal in the central sections above 300° cannot

be tolerated.

Concerning elements reinforced with welded reinforcements

of soft steel worked in the cold (6,000 kg/cm^) the limit of

resistance does not differ from that of elements reinforced

with ordinary mild steel.
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- 12 -

The irreversible decrease in resistance for this type

of reinforcement begins to manifest itself (above 5^) only

when a temperature of 450° is reached, (fig. 8) namely,

shortly before the finish of the plastic failure. The

residual deformations are also relatively small compared

to the total deflections because the working stress for this

type of steel (2,800 kg/cm^) is not very high. Fig. 9 shows

the total deflections and residual deflections of a ribbed

panel with welded reinforcement of cold drawn steel wires.

Heating the wires up to 490° formed an irreversible deflection of 13 mm which is not more than l/240 of its span.

The use of deformed steel does not Influence the limit

of resistance to fire of the concrete because an irreversible

loss of resistance of this steel does not begin to show itself before 500 ° (7^) namely at the time of the formation of

the break.

The experiments of the Institute have also shown that

elements reinforced with special hot rolled steel "25 GS"

(limit of elasticity 4,000 kg/cm"^) have limit of resistance

to fire slightly above those of constructions with reinforcements of mild ordinary steel (steel No, 3) or with welded

mesh of steel wire of 6,000 kg/cm'^^

The formation of the plastic break did not appear until

570° and the residual deflections Just before the finish of

this break did not exceed 0.01 of the span and no irreversible

loss of supporting power was discerned.

CONCLUSIONS

1. The limit of resistance to fire of simply supported

reinforced concrete elements is attained at the moment of

the plastic failure (when the limit of the elasticity of the

pre-stressed steel is attained) , Just before the formation of

this break irreversible deflections do not exceed 0,01 of span

and the irreversible losses in supporting strength and rigidity

remain within the limits of toleration.

2, The limit of resistance to fire of prestressed elements,

also pimply supported, reinforced with steel of 15^000-18,000

kg/cm strength, is approached when the heating of the metal
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reaches 200-300 , Above 300*^ the irreversible loss in

supporting strength begins to increase at very rapid rates^

whereas at temperatures slightly above 200° the irreversible

losses in rigidity exceed the toleration affixed at 20^.

For the cold drawn steel of 8,000-12,000 kg/cm"^, the

maximum heating tolerated must be determined by further

experimentation.

3» For elements with ordinary reinforcements, restraint

at the supports permits the Increase of limiting resistance

if the relation between the effective section of steel at

the supports and on the span is not Inferior to 2. For

prestressed elements reinforced with steel HR restraint at

the supports does not produce an Increase in the limit of

resistance

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USCOMM-NBS-DC
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Figure 1 , Characteristic temperature-time

curve for a fire involving wood.

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Figure 2, Standard and experimental temperature-time curves

- - - - standard curve experimental curves

Figure 3* Temperature variations at various depths

within a constructl9n element exposed to

both standard and experimental tests.

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Figure 7» Redldual deflections of reinforced concrete

constructions as a function of heating time

and of the temperature of the steel

A - Concrete beam reinforced with mild steel

1, 2, 3 - Ribbed prestressed panels with HR steel of

18,000 kg/cm2, strength simply supported

Ta - Temperature of reinforcement

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1. HR ^teel wire of 20^500 kg/cm^ strength d = 2.8 mm

2. HR steel wire of 18,000 kg/cm^ strength d = 2.5 nmi

3. Cold drawn steel wire of 6,000 kg/cm3 strength d = 5*0 nim

h. Cold deformed bar d = mm of ^-,900 kg/cm2 yield strength

/

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Figure 9» Deflections and temperature of a ribbed panel

simply supported reinforced with welded wire

fabric

‘ (span 3.10 m, cover 10 mm <3^z/(Ta - 1.7^= 6000 kg/cm^)

1. Total deflection

2» Reversible thermal deflections

fth= l2 + fo

° ho

Ta - Temperature of reinforcement

Tb - Temperature of compressed concrete

U.S. DKPARTMEINT OF COMMERCE

Kri ll, rii k II. Mu. Ill r. Si in lury NATIONAL lJURKAU OF STANDARDS

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

The scope of activities of the National Bureau of Standards at its headquarters in Washington, D.C., and its major

laboratories in 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 in 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, D.C.

' Electricity and Electronics. Resistance and Reactance. Electron Devices. Electrical Instruments. Magnetic Measurements. Dielectrics. Engineering Electronics. Electronic Instrumentation. Electrochemistry.

Optics and Metrology. Photometry and Colorimetry. Optical Instruments. Photographic Technology.

Length. Engineering Metrology.

Heat. Temperature Physics. Thermodynamics. Cryogenic Physics. Rheology. Engine Fuels. Free Radicals Research.

Atomic and Radiation Physics. Spectroscopy. Radiometry. Mass Spectrometry. Solid State Physics.

Electron Physics. Atomic Physics. Neutron Physics. Radiation Theory. Radioactivity. X-rays. High

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Constitution and Microstructure.

Building Technology. Structural Engineering. Fire Protection. Air Conditioning, Heating, and Refrigeration. Floor, Roof, and Wall Coverings. Codes and Safety Standards. Heat Transfer.

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Digital Systems. Analog Systems. Application Engineering.

• Office of Basic Instrumentation. • Office of Weights and Measures.

BOULDER, COLORADO

Cryogenic Engineering. Cryogenic Equipment. Cryogenic Processes. Properties of Materials. Gas Liquefaction. Radio Propagation Physics. Upper Atmosphere Research. Ionospheric Research. Regular Propagation

Servic(;s. Sim-l^artlT'Relationships. VHF Research. Radio Warning Services. Airglow and Aurora. Radio

Astronomy ami Arctic Propagation.

Radio Propagation Engineering. Data Reduction Instrumentation. Modulation Systems. Radio Noise.

Troj)os|)hcric Measurj'mcnts. IVopospheric Analysis. Radio Systems Application Engineering. RadioMeteorology. Lower Atrnos|)hcrc Physics.

Radio Standards. High Frequency l'dcctri<-al Standards. Radio Broadcast Service. High frequency Im-

• pt'damu; Standards. EI<‘ulronic (Calibration Center. Microwave Physics. Mit'rowave (Circuit Standai'ds.

Radio (Communication and Systi'ins. Low FrcipiciK'y and V<‘ry Low f’l'cipicncy Research. High I'rc- qiiency and Very High Frcijiicncy Ih'scarch. Ultra High f'rc<|iicii( y and Siqu'i' High I’rcquc'iicy Rc'scarch. Modidation R(;search. Antenna R<'s(*arch. Navigalion Systems. Syslcms Vnalysis. I'^icld ()])cralions.