ht . mi wiyp.y..li,i.ip,n. ti.jm l.1. .m -i - -.. .). .;,m ... · tll»j»».i^iiu^»».^ ipil «...
TRANSCRIPT
HT""™ ' ™ . mi ■■ Wiyp.y..li,i.i.....p,n. ...ti.jm .1. .m -i - -.. .). .;,m,llm p.r-"^...^! ..tll»J»».i^IIU^»».^ ipil« l«|l WWW WM»"«"' M»P »• fM4UIIIW.HWII«
AD-783 434
HEAT TRANSFER PROPERTIES OF MILITARY PROTECTIVE HEADGEAR
G. F. Fonseca
Army Natick Laboratories N a tick, Massachusetts
January 1974
DISTRIBUTED BY:
urn
^
National Technical Information Service U. S. DEPARTMENT G? COMMERCE 5285 Port Royal Road, Springfield Va. 22151
- ■ - — - '■--■■-"- ■JimntMliliri
""" "■•<■■»«»■■"■»■ ■ ~- ■"'■■■" ■ »■■■wniw...... ^. .. .„,„„....,„ .,,.,.,,.».„... ,,».„■«....,■ uwnBiy^.^
Approved for public release; distribution unlimited.
Citation of trade names in this report does not constitute en official indorsement or approval of the use of such items.
Destroy this import when no longer needed. Do not return it to the originator.
■A
■ r ii i rtwaiillMl fi-SS
111,1111,11 ""' '' ' iv ^w,iwm'npi.',«i i iimw j.I »■ ii11inii. 1I1H4LHIIHW-."""1 i" " .«■H-ILI JI .I"«',» I <•>■ ■!■•• »>'.'!'*JJ»
Unclassified S»cuiity CI«niflc«tion ADlfo&t
DOCUMENT CONTROL DATA R&D (Security c'»99lttcmtion of till; body ol mbatrmel mnd indonlng annotation muml bo MNfrt whan tho pwifl rmpotl !■ clamoltiadj
1. ORIGIN A TINS ACTIVITY fCrrporafa author;
US Army Natick Laboratories Natick, Massachusetts
aa. RCRORT ICSURITV CLASSIFICATION
Unclassified ab. ORCUR
1. RCRORT TITLE
Heat Transfer Properties of Military Protective Headgear
m. oucniPTivt NOTEf (Typ* ol »port and Inclmlro dato«; Research report
I- AUTMORIS» (Flm mS», SfäflK Inlttml, laat nSwJ
G. F. Fonseca
*. RCRORT 0<TI
January 1974 •a. CONTRACT OR BRANT NO.
•• "«OJICT NO. 1T762713PJ40
ra. TOTAL NO. OF PAGES
ya 76. NO. OF REFS
11 •a. ORiatNATOR'l REPORT NUkTBCRIS)
74-29-CE (C&PLSEL-121)
OTHER REPORT HOW (Any thlt nporl)
othor number* »at may b» aaolanod
10 DISTRIBUTION STATEMENT
Approved for public release; distribution unlimited.
II. SUPPLEMENTARY NOTES
\
12. SPONSORING MILITARY ACTIVITY
US Army Natick Laboratories Natick, Massachusetts
a1. ABSTRACT
The heat transfer properties of headgear have been determined in chamber studies using a physical model (copper manikin). The evaporative heat transfer (im/clo) from a head in "still" air was constant above a standoff distance of 1.270 cm. for helmets with a constant head area coverage (67%). Reducing the head area coverage from 67% to about 50% was necessary to increase the evaporative heat transfer for a hälmet standoff distance of 1.270 cm. The effect of wind on the heat transfer properties of selected headgear with varying designs was to decrease the values of insulation (clo) by about 60% and increase those for the evaporative heat transfer (im/clo) by about 4 times the "still" air values.
•:, ID: .'. " INPOP*, A' li iN '-;l :' '
f\r» ■Off« 1 A 11 •«•LASMI *«m wet.' JA" ' "H'e" * Unclassified
Security ClanalficatJon
lM||Mii|i^llglaM»>ai»«.»i»iMiwi«n.»»' -'-
^^^^^^^^^^—^
Unclaasifi«d Security CUtalflcaUon
KIV «OKI *
Heat transfer Insulation Evaporation Headgear he lmets Heat Stress Ergonomics
«•* Unclassified Security Claaalflctt'MI
■IHM i«#«lHMMNlMMI«ritfMU*> •riWM»«««^ »*nrt<M*i»r»i ■irvniff«!
»■■niii'PiWJ. mill mpiim i i HUI in i.immun ppppnW HJW»I i. Li >■ ■■ " »,"■". «i'<.n«tm.mffm'nmmw-' rm,nm.rm i..nm,ii||pwiw.t»wil.'lii muH"*u*y>|i|l,inw»VSJ
Approved for public release; distribution unlimited.
AD
TECHNICAL REPORT 74-29-CE
HEAT TRANSFER PROPERTIES OF MILITARY PROTECTIVE HEADGEAR
by
G. F. FCNSECA US Army Research Institute of Environmental Medicine
Project Reference: 1G662713DJ40
Series: C&PLSEL - 121
January 1974
Clothing and Personal Life Support Equipment Laboratory US Army Natlck Laboratories
Natick, Massachusetts
< i
II
i i in m: »■ ■ „—-.—— — «>»« *-^ -'■ -
1WWIUIW11UIU.I« mmmm -■* 'WM»" ■ > »"-■' 'i»n ji»»iiii!Miiwii,nin.iiii!aiPww.wnt.uiiiw»ii ..«M^IH"
I
FOREWORD
For the first time, a systematic study of military helmet design variables and their effects on heat transfer from the head is available. This study is one of many interdisciplinary efforts Involving materials, ballistics, human factors, systems analysis and engineering design which form the technical bases upon which a new infantry helmet design will rest.
The new infantry helmet is being developed under the Army Materiel Command Five Year Personnel Armor Program. Project officers, W. D. Claus, L. R. McManus and P.E. Durand, were responsible for the work unit under which this study was carried out. The project officers designed and supplied custom shells for the head of the copper manikin conforming to the parameters of this experiment which included variable stand-off and variable area coverage. In addition, production helmets were provided from C&PLSEL's collection of world-wide military headgear in order to establish base line comparisons. The work was performed by G. F. Fonsece of the U.S. Army Research Institute of Environmental Medicine, Military Ergonomics Laboratory.
The author wishes to thank Dr. Ralph Goldman, Director, Military Ergonomics Laboratory, for reviewing the report.
i
ill
■- -- ■- —««.■■■■i- A
ijipwmwi' ■ IU"»1 wpwu^H! j 9[, iwt'iiiWBgppuff.Jilt i. i.J iu pffWBBWff i" .miii*«iiiiPti'iiiiiipi.i'.wiii»^wwpw*. \ i !JpwBMHpww."Pf■ ■." " ■■" wwwv""ir»^r
TABLE OF COHTEHTS
List of Tables
List of Figures
Abstract
1. Introduction and Background
a. Review of Existing Physiological Head Studies b. Review of Published Heiset Studies
2. Pvevious USARIEM Heat Transfer Studies on Helmets with Ventilating Features
3. Outline of USARIEM Experimental Techniques
4. Thermal Properties as a Function of Standoff Distance from the Head
5. Effect of Ventilating Slots in the M-l Helmet Liner on Evaporative Heat Transfer
6. Area Coverage Effects
7. Removable Suspension Systems for the M-l Helmet Liner
8. Face Shield Effects
9. Thermal Characteristics of Selected Helmets
10. Discussion and Conclusions
11. References
Page
v
vi
vii
1
1 1
2
5
15
15
19
19
30
30
32
lv
mm 11 mm —-
LHWUBUI, i in „„„*..,*:„ i , i i .a....I.....I..1.,, jLiiii.in nmu i» tm.m i i"—n» w i ■iiiiiyiijiiLiiMiiniw.in. i.iimuw>mi^» i ,WM i-" "»«
LIST OF TABLES
I Thermal Characteristics of Original Hayes-ftevart Helmet
II Thermal Characteristics of the Standard West German Tankers Helmet
III Thermal Characteristics of Experimental Helmets with Different Standoff Distances from the Head
IV Thermal Characteristics of the M~l Helmet Liner with and without Ten Ventilating Slots which Provide Open Spaces Equal to 8% of the Total Helmet Liner Surface Area
V Thermal Characteristics of Experimental Helmets with Different Head Area Coverage
VI Total Theraal Characteristics in "S-ill" Air of a Tropical Combat Fatigue Ensemble Using the M-l Helmet Liner with Removable Suspension Systems
VII Thermal Characteristic« of Selected Removable M-l Helmet Liner Suspension Systems
VIII Thermal Characteristics of the Standard M-l Helmet and a Commercial Riot Control Helmet with a Face Shield in the Up and Down Positions
Pa^q
4
IX Thermal Characteristics of Selected Helmets
11
16
17
22
23
25
28
-- -- ■Tu.. ■mir-
inpu in.111 II...I I.L l*ll -T^II.'J.I.I. H »»llllll Uli,' ■'» ' HI' I Mi»« II . Ml I J " "I I Ulf*t..JI!l r^^- ,-.. .1 ,.i, . i.naijHUWU 1
LIST Of FIGOHi*
1. Photograph« of the Original Bayce-Stewart Helmet: (i) Front View, (b) Sldo Vlow
2. Photographs of the Standard West Gorman Tankers Helmet: (a) Front View, (b) Side View, (e) Interior View
3. Photograph of the Sectional Manikin Dressed in Tropical Combat Fatigues
4. Photograph of 4 of the 5 Experimental Standoff Helmets Showing, Left to Right: 2.540-cm., 1.905-cm, 0.635-cm., and O-cm. Standoff Hairnets
5. Curves of Clo (a) and Im/clo (b) ae Functions of Helmet Standoff "ietence
6. Graphical Preaentation Demonstrating the Combined Effect of Clo and Im/clo Valuea in Terms of Theoretical Environ- mental Limits for Thermal Equilibrium of the Head for the Five Experimental Standoff Helmets: (a) "Still" Air, (b) Air Flow of 3 Meters/Second
7. Photogreph of M-l Helmet Liner Showing Location of the Ten Ventilating Slots
8. Curves of Clo (a) and Im/Clo (b) as Functions of Head Area Coverage
9. Photographs of Three Removable M-l Helmet Liner Suspension Systems; (a) Standard, (b) Welaon-Devis, (c) HEL
10. Photograph of the M-l Heimat Liner
11. Photographs of Helmets with Face Shields: (a) Standard M-l Helmet, Face Shield Up; (b) Standard M-l Helmet, Fece Shield Down; (c) Commercial Riot Control Helmet, Face Shield U^; (d> Commercial Riot Control Helmet, Face Shield Down
12. Photograph« of Selected Halmata Presented in Table IX: (a) Aircrew AFH-1. (b) Aircrew APH-5, (c) Standard CVC (d) English Infantry, (a) Football Helmet, (f) Experimental Hayee-Stewart, '%) Italian Infc**t«p( (h) Experimental Parachutltit Li. it
13. Graphical Preaentation Demonstrating the Combined Effect of Clo and im/clo Values in Terms of Theoretical Environ- mental Limits for Thermal Equilibrium of the Heed for Two Helmete from Table IX: Iteilen Helmet (One of the Lergeet im/clo Valuee) and the Aircrew APH-5 Helmet (Smallest lm/clo Value); (a) "Still" Air, (b) Air Flow of 3 Meters/Second
Page
3
10
12
13
14
18
20
21
U
26-27
29
FMÜ A
&■•-■•-'.■■ wmmmt*'mtm*.im!)it>H*mmyik^? i.i iniiniinnj.i^wniw.ni ..inn,;, nnanpi.il iim.in..,iiLuiii>ij. ■>. I.TI" ■ ■■! «i....i,.B..Ti^,;TrT.jl|lnu„i„ii U-UU..TPT .p.-.i
ABSTRACT
i
The heat transfer properties of headgear have been determined In ch&aber studies using a physical model (copper manikin). The evaporative heat transfer (lm/clo) from a head In "still" air was constant above a standoff distance of 1.270 cm. for helmets with a constant heaH area coverage (67Z). Reducing the head area coverage from 67% to about 50% was necessary to Increase the evaporative heat transfer for a helmet standoff distance of 1.270 cm. The effect of wind on the heat transfer properties of selected headgear with varying designs was to decrease the values of Insulation (do) by about 60% and Increase those for the evaporative heat transfer (lm/clo) by about 4 times the "still" air values.
vll
■ —*
cap i_, « .«I.U.I.I ■"" ""•'-, ~ "•"'" ■ .i.i.ii.piiniii iiiumi, , ,n 11 .in i i ,i i ■ , ■ „ i , --, — •»'"'— r ,ip.«Jip!l."i!i. i ■■■
INTRODUCTION AND BACKGROUND
The U.S. Army Research Institute of Environmental Medicine is providing physiological research support to the AMC Natick Laboratories program for the design and development of a new helmet for the infantry soldier. This study, as part of this support, presents a review and analysis of experimental approaches usi"g data (clo (6), im (11), and im/clo) obtained on the sectional manikin. Thermal evaluations, measured under both "still" and forced air conditions of available standard U.S. and foreign helmets are also included.
a. Review of Existing Physiological Head Studies
Three publications are of particular interest in any study of the heat transfer properties of headgear. Siple (8) stated that exposure of the head in the cold accounts for a large percentage of body heat loss since heat is lost in Increasing quantities from the head as the thermal gradient increases. This prediction was verified by Froese and Bjrton (5) who directly measured the nonevaporative heat losses from a bare head using a temperature gradient calorimeter. This study showed that because there is little or no vasoconstriction in the head when it is exposed to cold temperatures, the heat loss from the head amounts to half of the total resting heat production of a man. Finally, Edwards and Burton (3) investigated the distribution of skin temperature over the surface of the head and presented a figure showing a detailed mapping of these surface temperatures.
b. Review of Published Helmet Studies
Winsmann;s report (10) deals with the thermal protective character- istics of a CVC (Combat Vehicle Crewmen, e.g. tankers) helmet in arctic and hot environments. His results were based on head temperatures and subjective comments and indicated that the CVC helmet provided environ- mental protection equal to the field, pile, cap at 23.4C air temperature and about 1.3 meters/second air flow. Environmental protection in a heat stress situation was about equal to the field, cotton, cap at 29.4C air temperature and about 1.3 meters/seccnd air flow.
van Graan and Strydom (9) investigated the effect of reduciig heat stress by providing ventilating holes in helmets. They compared a helmet without holes with a second helmet with two 1.27-cm. diameter holes at the top of the helmet and with a third with six equally spaced 0.635-cm. diameter holts around the circumference of the helmet. These helmets were compared on the basis of temperature results using three thermocouples, one located at the top of the subject's head, another spaced 2.54-cm. frcm the top of the head, and a third placed at Che inside crown area of the helmet.
m^mM -—— — «■■Ill I
■<-"■■«"- ,iii, .i MI ■ ... ■ I »up Ml I -—.-""--- -.--■ - -
1
Their results showed no difference In heed surface temperature or helmet surface tempersture among the three helmets. The sir temperature above the head shoved no dlffersnce vesting the helmet without halee or the helmet with two i.27-ao. diameter holes at the crevn of ehe helmet. However, the results for the helmet with six equally spsrid 0.635-cm. diameter holes around the rim appeared to indicate that the Inside helmet air temperature at the thermocouple measuring poslltlon vss higher with the six holes than with the two 1.27-cm. diameter holes or no hols for the cool elr environmental conditions when the subjects were et reet and registered e lower temperature when the eubjecte were doing s step test In the hot dry condition. These letter two findings appear to indicate thet some of the incoming elr was diverted through the six holes around the rim of the helmet rather than passing over the top of the heed. However, these air temperature differences had no significant effect on heed cooling rince for ell helmets, heed end helmet temperstures showed no difference for any of the reepective experimental conditions sn<* «ubject activity levela.
Coleman and Mortagy (2) studied the heet retention qualities of five different models of footbsll helmets. These helmets differed primarily in the design snd composition of their suspension systems. Air tempera- tures measured "with thermistors inserted 2.5-cm. into the right enterior end left posterior quadrant of eech helmet" ahowed a significant differ- ence among the helmets with web suspension systems (lower eir temperatures), and those with form fitting inflatable and hammock-suspension systems.
2. PREVIOUS USARIEM HEAT TRANSFER STUDIES ON HELMETS WITH VENTILATING FEATURES
Both "snugly-fitting" snd "close-fitting" hesdgssr with ventilating holes wsrs studied .{DF reports ME-E6-69 snd ME-E11-70) using s physical model (electrically heeted sectional copper manikin). A "close-fitting" original Hayes-Stewart helmet containing an air ventilation opening et the top (see Figure 1) wee evaluated en the manikin to determine if this venti- lation opening significantly improved heed cooling In "still" air or In air flows up to 5 meters/second. Table I shows thet the ventilating opening provides little advantage la increasing evaporative heat transfer (lm/clo) from the heed In "atill" air condltlone, although with the higher elr flows there eppears to be e slight advantage; both helmets provide en eir space around the heed which le readily disturbed in wind.
A "snugly-fitting" standard West German tankers helmet consisting of s foam-rubber liner and reinforced from ahull to nape of the neck by e flexible polyethylene otrlp vae also studlsd. Ventilation la obtained et the eldea b*- 3 screen grommets snd through two sir passages running from the front to the beck of the heed (see Figure 2). Thle helmet vss evaluated on the manikin to determine the effect of the air-ventilating grommets on the evaporative heet transfer (lm/clo) from the heed. The results shoved that seeling the ventilating gveemwts on the side of the helmet made little difference in the evaporative heet trenefer from the heed In "still" elr.
i ii war*°— - - ■ - .
HI \m\\wmmcwmi&m*&rw*^***m*i^^mi>™"".m^^*~'**^^r^m^mrw**Y^ "w.'i*ti*w'^i'i*'i^*w^n
Figur*» 1. Photographs of the Original Hayes-Stewart Helmet: (a) Front View, (b) Side View
— MMMMMÜ
tmmmm mim-J-» iu»w '•"»- .„^.„.„■^....ii,. ... —■.'. ■ ■ ■■'« IU.I.....«« •«■ - ■ ■JjpilHlljl!
TABU X. Thtrmal Characteristic« of Origin*! Hayt«-St«wart Helmet
Air Flow
Headgear "Still" Air 2 Mater«/Second
CLO lm/CLO in CLO lm/CLO la
Hairnet Helmet/Ventilating Cap Bar« Head
1.12 0.49 0.91 0.50 0.64 0.97
0.55 0.45 0.62
0.53 1.2 0.64 0.49 1.3 0.64 0.43 1.6 0.68
5 Meters/Second
CLO im/CL0 in
0.42 2.4 1.0 0.38 2.6 1.0 0.33 3.0 1.0
ass mm-
iWMWMMi. ■■ |iwi iJi .m>mmum,,mmivii>wimmni.,..UH**i». " '- ...in-nmF'i ,i...11 .miii iij^ii.iut.iCT-wwi ^w.nniip]niiii!jj.mM^i"w|^-,'»,*",»'^w^w^W^
However, In an air flow of 3 meters/second, sealing Chase ventilating gronunets reduced the evaporative heat transfer by about 10Z (see Table II). Apparently, since this helmet fits snugly to the head, Increasing the air movement around the head with the ventilating grommets sealed has little effect on the evaporative heat transfer from the area of the head covered by the helmet.
3. OUTLINE OF USARIEM EXPERIMENTAL TECHNIQUES
Headgear heat transfer properties are being studied in support of the AMC 5 year armor program by USARIEM. Manikin head section do, im, and lm/clo values were determined by the methods described in an earlier paper (4) following the standardized, experimental procedures set forth in the Standard Manikin Procedure memoranda (2). The head section of the manikin is considered as the test section; the remaining five sections (torso, arms, hands, legs, and feet) are considered as guard sections. The manikin is completely enclosed In a skin of form-fitting underwear material and dressed in a basic clothing ensemble consisting of tropical combat fatigues, 1 pair of socks, and a pair of black leather boots (see Figure 3). In these studies, the manikin was placed in a standing position near the center of an environ- mental chamber facing two fun« which directed air at the head of th* manikin. A helmet was placed on the manikin's head and the insulation value (clo) was determined for normal chamber air flow (i.e. "still" air condition, with the two fans off) and for a forced air flow condition (i.e. with the two fans running). Similarly, after the manikin's skin (underwear material) was wet, the evaporative heat transfer value (lm/clo) was determined for the "still" and the forced air conditions.
4. THERMAL PROPERTIES AS A FUNCTION OF STANDOFF DISTANCE FROM THE HEAD
There was little or no systematic data on the evaporative heat transfer cooling range (lm/clo) for any close-fitting helmet system. Such information for a selected close-fitting helmet configuration, added to Information on similar helmets with less or greater spacing distances from the head, should define an optimum spacing from the head for evaporative heat transfer, if any such optimum exists.
A master mold of the manikin's head was made, and a set of molds were cast which contained a controlled amount of standoff. Five helmets were vacuum formed with standoff distance from O-cm. (snugly-fitting) to 2.54-cm. (very loosely-fitting) in 0.635-cm. increments. All five helmets provide a constant head area coverage of approximately 67Z of the total manikin head surface area (see Figure 4).
UF "!UUL iqmnmpppip^^nn. ■!■ vii «ii ■• J<*^« in vnlvMii jipi.iiiiii I« IIPIII ii -*« " ■' '•■>iM-«lpiiHp>iipi^mmrr^^wmimmmmmn^m BIW1""WP"»>^^WWW^PWH«
Figure 2. Photographs of the Standard West German Tankers Helmet: (a) Front View, (b) Side View, (c) Interior View
• HMMltll^UB
INM I III« 1.1 — ppnppjpmpimp»>P>",«P«UI,.II ijl.in™...WiiH!..iw«nij,iu. '.m-»mi MI in. 111,n,u... mi.www» II■ ii ii i fii«„iuiii«iipii«i«aa
TABLE II. Thermal Characteristics of tlie Standard West German Tankers Helmet
Jeadgear
Helmet/Ventilating Holes Sealed Helmet/Ventilating Holes Open
Air Flow
"Still" Air CLO lm/CLO lm
3 Meters/Second CLO lm/CLO lm
1.49 0.17 1.46 0.18
0.25 0.26
0.87 0.69 0.83 0.77
0.60 0.64
— - «I Ti »■■ «■ llir II11" '' ■«■I—m»»—»»«» ** _^i. ... -■*..
,mmmmmmf^^~~ 'iw«"""'! ----- W I^V* Jllipiu Jl «L^"' I.^MJ».».--<—--i~ *l»|lj.UWII.|p^| ll,..^«!!..^."-
Figure 3. Phoograph of the Sectional Manikin Dressed in Tropical Combat Fatigues
J«««B^^_ — ■ MMM f»W" li> — ■
,..m in ■■■■iiii-i mm i n ,^--^- ."»'■'M'" ,111." -,... - ,,„,| ■-,_■..■.—.V»*"-*.».,,WI" " ■ I ■ '. II I »-W11—■!—, •»>> .»iiiiii,.«»n.n...»,i»^i..»., ■ WITKIWW:'»!
The results (see Table III) show that helmet No. 1 with O-cm. standoff, practically eliminated any evaporative heat transfer from that area of the head covered by the helmet; essentially all the evaporative heat transfer from the head occurred over the uncovered area of the head (about 33% of the head surface area). Furthermore, for the '"btill" air condition, there is little difference In lm/clo between this helmet which fits snugly on the head, and the one (helmet No. 2) spaced 0.635-cn». away from the head. Apparently 0.635-cm. spacing around the top of the head consists o.~ essentially dead air space. Once the standoff distance reaches 1.27-cm., there is little difference in lm/clo among the 3 helmets covering the 1.27 to 2.54-cm. spacing range. Thus 0.635-cm. is too small to have much effect on evaporative heat transfer in "still" air while 1.27-cm. produces as much as 1.905 or 2.54-cm. Figure 5 shows insulation (clo) and evaporative heat transfer (lm/clo) as a function of standoff distance for these 5 helmets. It is seen that the insulation values (clo) reach a maximum value at a 0.635-cm. standoff distance and then decrease with increasing Ok<mdoff distance.
Although In "still" air the snugly-fitting helmet (0-cm. standoff distance) showed the lowest insulation value, because there was no air space to provide Insulation between the head and the helmet, at 3 meters/second the snugly-fitting helmet provides greater insulation than any of the other helmets, except for the 0.635-cm. standoff helmet; the "dead" air space between the helmet and the head at standoff distances beyond 0.635-cm. 1B now disturbed. Conversely, the evaporative heat trans- fer from the head, which did not show an Increase in "still" air conditions until the 1.27-cm. standoff distance was reached (again because of the dead air space with the 0.635-cm. standoff helmet), with moving air (3 meters/ second) shows a disturbance of the "dead" air in the 0.635-cm. space; the value for the 0.635-cm. standoff increases toward the nearly constant evap- orative heat transfer value of the 1.27, 2.005, and 2.54-cm. helmets. Figure 6a is a graphical presentation which demonstrates these combined effects of the clo and lm/clo values for these 5 helmet standoffs, in "still" air, in terms of the theoretical environmental limits at which thermal equili- brium could exist with respect to the head area of men who need to lose 25 watts from their head surface. The lower ambient temperature limits for the helmets are given by the vertical lines on the left side of the figure. These vertical lines are based on the insulation value (clo) of a given helmet and represent the lowest ambient temperature at which thermal equili- brium of the head can be maintained. The concept of environmental range is not considered in this clo calculation but occurs when both clo and im/clo values for a given helmet are considered. These values (clo and im/clo) give the sloping lines on the right side of the figure and represent the upper environmental ranges for thermal equilibrium of the head. Within the area bounded by a vertical line on the left ani a corresponding sloping line on the right, all combinations of ambient temperature (horizontal axis) and ambient air vapor pressure (vertical axis) will allow a fixed rate of heat
• ■ ■■ -
IN I ~ J—
WHWWIIH i.I'Mi.'lll'H! ."
fl
to B 4-1 U
o
0 • "2 S c u td i *-> IT) to o
a» r-\ • CD r-l 4J c - 01 •
^ B M I V o a-»
es a) io a
•• H gj u II
J2 X. tC 4J 00
•H 4-1 i*-. pci >*-i O O
O T3 ■^ u a U-l V V O M-" tO
01
a B • H 60 8 60 (3 I O -H O
Pui CO (0
(D
10
........ ... -■in I »i ... «.J >.a>ii..IMil.pi.i>illii.ij - . ii. ,* .ii.«.u i ,..n, njiijup^ppT.^^.p^i .!■■ ii ,.i. ,i .I.IIIH.I,IH,,IH»- im,., i. -
TABLE III. Thermal Characteristics of Experimental Helmets with Different Standoff Distances from the Head
Standoff Air Flow
Helmet Distance "Still" Air 3 Meters/Second Number CM CLO im/CLO im CLO lm/CLO im
1 0.000 0.88 0.33 0.29 0.42 1.1 0.46 2 0.635 1.08 0.33 0.36 0.47 2.0 0.94 3 1.270 1.07 0.40 0.43 0.41 2.3 0.94 4 1.905 1.05 0.44 0.46 0.39 2.3 0.90 5 2.540 1.00 0.44 0.44 0.37 2.3 0.85
11
■ — — ■ - - ■ - ■ -- -I Mill II "-— ll—ll ■■■Ml I.
' I »»II w^^^ •«•»*'." • '" ■""««.I I ■<»'»■' — .11 j i ii n^win K.....1 , ....... , I,. I ,II^,.VIV. ... . .,.** «—- .. ,„,.„„™.^»^,
ono
. $5
5 ■<
o 3 o
o "} o
3
o
- 8 8
ä
o K fc 3
<r
3
ch o
ö ES
I«
O t o
J V
c o
U
§
<a
o H U
s ^. 41
s o w
tH CO
IM O <M
a o
U (/I
in
41 M
OTTO cay*»
12
Hmrtrw ~m fcim" ntlit ■•dowiuMbB ^.^^ _^., Mif>i
mull mil. l.imumwH •»mi'Mimmimmmwsm ■ ...in.,. . .,,.,,.i..^-q—^j-m....».....*.! I.WH.I.W,^ | i HI, ,||| |j ,„ n.mjiuju, -■-....■..^,... -n.»w
i i r i I i i
CRT BULJ] TtMPER*'U«»[ «C
JO «p I I I I I I I I I I I I IIUJL
»3fnX" AIB
HEAT LU33 FROM HEAD ■ 25 MATES
»IN tSHPERATURE
}2.2* C (L0*B BOUNUART) 35.0« c (UPPER BOUNDAKX)
///7 / / ••/ / / / / / /// / /
/ / /
/ / / / / / / / / ///
mm awwrr tttJ ft ' / *,,f/t J / /
' r
SO 4ft
i—mrnrn
DNT tUL' Tl MHIUTUftf
Figure 6. Graphical Presentation Demonstrating »-he Combined Effect of Clo and Im/clo Values in Terms of Theoretical Environ- mental Limits for Thermal Eqillbrlum of the Head for the Five Experimental Standoff Helmets: (a) "Still" Air, (b) Air Flow of 3 Meters/Second
13
■■■■-■ - - **—""ii ... - — ....,,.,—..._.—
-—-n~mv<i«w>i.«piM,*Bai ■'» ' " ' mmmmmmm • i .i,IH.M«W!»ti. W.IIJ TT-W..-^ ^wr«iÄWpHWM(ivr>r-^w-^-^ ' ■■ wiMffW.i*WW?y^W^i
Figur« 7. Photograph of M-l Helmet Liner Showing Location of the Ten Ventilating Slots
14
I ,iu UHIII ii """"^ "Wl. n.piinm»»i i —■» i ..■i-ii" i-iimju.»»!!!!! i i.i | ■j. j ■ nnn^—JT^^^nywiW—Tjiy'■W1W >■ i.l"".'. «"■
I
loss of 25 watts from the head. To the left of a given vertical line the heat loss from the head will be greater than the 25 watts equilibrium value. To the right of a given sloping line the heat loa-j from the head will be less than the 25 watts equilibrium value. This figure presents a simple pictorial representation of the theoretical environmental range over which thermal equilibrium will be maintained in "still" air. A similar graph for wind is shown in figure 6b.
5. EFFECT OF VENTILATING SLOT'S IN THE M-l HELMET LINER ON EVAPORATIVE HEAT TRANSFER
Although neither the helmet study discussed previously using a venti- lating cap at the top of the original Hayes-Stewart helmet nor the study comparing miners hard hats with ventilating holes showed any significant Improvement in the ventilating properties of the respective helmets, a further look at air ventilating holes in helmets was undertaken to see if a combination of ventilating holes at the top and around the helmet equal to about 8X of the total surface area of the helmet would she- a difference in im/clo in "still" air. A M-l helmet liner was modified by cutting ten ventilating slots equal to about 8Z of the total helmet liner surface area. Two of these slots are located on each side of the helmet, two in the rear, three in the front, an! one on top of the helmet (see Figure 7). It is apparent from the results given in Table IV that this amount of open area in a helmet and the location of these ventilating slots does allow an increase in im/clo in "still" air, but has little effect at an air flow of 3 meters/second. Since this helmet liner is spaced about 1.27-cm. from the head, these results are important in illustrating the order of magni- tude of ventilating holes and their location around this type of "close- fitting" helmet.
6. AREA COVERAGE EFFECTS
The effect on the heat transfer properties of helmet head area coverage was Investigated by removing three 2.54-cm. strips from the bottom edge of the experimental helmet with the 1.27-cm. standoff distance. This provided four helmet samples covering the area coverage range from 47Z to 672. The results are given in Table V. The clo and im/clo values are plotted against head area coverage in Figure 8. The clo values in "still" air decrease linearly with decreasing head area coverage; in an air flow of 3 meters/ second, they decrease until a head area coverage of about 55Z is reached and then they level off. The evaporative heat transfer (im/clo) values in "still" air do not show an increase until about 502 head area coverage is reached; they are relatively constant at an air flow of 3 meters/second. It is of Interest to consider the two extreme head area coverage helmets (67Z and 47Z head area coverage). The quantity of helmet material removed con- sists of about 30Z of the material of the 1.27-cm. standoff helmet. The Increase In im/clo In "still" air as a result of this decrease in head area
15
■ -ITT - - —
'"'<"" ' '-• - :---■—-■ ■- ■■■■-- 1-T« '■ ' WH! .1 UH.IIWIWV"" »■■'■!■■».■ ■ ■ .1 T" w.1. i.. ■ ■,..,■!. — ,..,, „i., „,.,.,
TABLE IV. Thermal Characteristic« of the M-l Helmet Liner with end without Ten Ventilating Slots which Provide Open Spaces Equal to 8% of the Total Helmet Liner Surface Area
Helmet Liner
Open Slots Seeled Slots
Air Flow "Stlli" Air CLO Im/CLO lm
3 Meters/Second CLO lm/CL0 lm
0.94 0.55 1.03 0*41
0.52 0.42
0.36 2.2 0.29 0.36 2.1 0.76
16
i
r BIIM..IUI MP,.,iiu-:.iHi|^^8p|(M|ffjBff^ ' ■ """"■"' WWWMW^W liWMPW11!»'-■'■■■■ '■'■■-''■■.i... " -fl-tw^'«1 w»J»4. .v., 11,, I, lau.ipMl
TABLE V. Thermal Characteristics of Experimental Helmets with Different Head Area Coverage
Air Flow Head Area Coverage
Z
S7 60 54 47
"Still" Air CLO im/CLO in
3 Meters/Second CLO im/CLO im
1.07 0.4Q 1.03 0.40 1.00 0.43 0.96 0.48
0.43 0.42 0.43 0.46
0.41 2.3 0.94 0.3r 2.0 0.70 0.32 2.3 0.74 0.32 2.4 0.77
17
■ip^pn „I.J.».UI.I>P.LWWH.W """■-■■'Jit.HWjy-w1"^'" ""-«.■ ■H.WI.IIIHI .IIIIIII i mumriM ..^mw--«vm>>™w,*!r*mmmmK'H,**w!*wiv»*»,i i.t.ii,[iWP,ipBiy,l"'wy <y> pupn.»-'n »»■iwipj^lgiWPIB
,J I
H O
3
s ä
/
I /
(713 3
• &
- 8
■I o <
o o
o
o
3 «
§ * o
n a)
\ o
\
013
• S
■ s
<»\
a
onyxi
s 8 1 I c_>
■ R
o f-4 U
3 5 ^
O 01
u ? B
°§ to u «I & s 3$
0)
s,
<no/Hi
18
w.■,^,IHWu,.w■■l.lJ.-^.Mlffw.Wriwl^''■^^l'^J"l'i»^' ^r^^wm^^a>-m.*<msmß.''irymma--mt^^m^^mmm,jwm^mKf>Mi.m.mmi>.>i >
i
coverage amounts to about 20Z. The helmet liner with the ten ventilating slots equal to about 8X of the helmet liner material Increased the im/clo abut 35X in "still" air. Comparing these results with the previous findings with helmets with ventilating holes indicates that the number and locations of these ventilating holes could be more Important than the total quantity of helmet material removed.
7. REMOVABLE SUSPENSION SYSTEMS FOR M-l HELMET LINER
Any given suspension system modifies the evaporative heat transfer properties of a helmet, in part, by the total head-suspension system contact area, the distribution of this contact area over the head, and the material composition and thickness of the suspension system. Three removable suspension systems (see Figure 9) for the M-l helmet liner (see Figure 10) were studied to determine if any measurable differences in the evaporative heat transfer (im/clo) from e head could be detected. An earlier study (8) using a single circuit copper manikin determined total do and total im/clo values for these 3 helmet liner/suspension systems as part of a complete ensemble. These experimental results obtained in "still" air are shown in Tvole VI. Since these values are for the total manikin surface area, the contribution from the head is masked by the contributions from the other areas of the manikin. Table VII shows the im/clo values for these 3 helmet liner/suspension systems determined on the sectional manikin. Although these im/clo values are grouped closely together, comparing the lm/clo values for the standard with those for the HEL suspension system suggest that the head-suspension system contact are*» becoaes more importanc with increasing air flow.
8. FACE SHIELD EFFECTS
A standard M-l helmet and a commercial riot control helmet (see Figure 11) were studied to determine the effec: on the heat transfer properties of the helmets when a face shield is worn in the down position. Table VIII show« that measurable differences in clo and im/clo were obtelned when these values were compared for the face shields in the up and down positions. The clo values increased by about 0.1 clo and the lm/clo values decreased by about 0.01». Increasing the air flow decreased the clo values of both helmet* with face shields in the up or down position by about 60Z and increased the im/clo values by about 4.5 times the "still" air values for the standard helmet and for the riot control helmet with the face shield in the down position. The riot control helmet with the fece shield in the up position showed about a 5.3 Increase in the lm/clo value with increased ait flow.
19
.«. ,, .,,„ u.-w ....,-..., ™~ ~ — -" '-" ■ ■■ '■■■■ •»■■■■— ■ in . ,M,,..rVm
c o
p. 0) a ,
CO t-l w
Vi 33 01 a ^ ■H o
at co 3 > ai id ss a
? i v at H is •2 > .O
« T3 M
V CO
n a 62
CO CM O /-*
cd Ä *-* o. C0 •*> u 00 o U 4J O CO
a* en
a« 41 U
s,
20
.mmimm ■•-■•■ -• ' . .—.....................—, -"■ ■■ ■-— -~ - ""■'"':»' HO in. . in "IHWIM
■y ■'"'\
*♦•' .'
I
Figure 10. Photograph of the M-l Helmet Liner
21
A
wmimmrnmmm" * WP«'."« .mimuMimm ><m< iw^ III««! li|»w«p«.i||l l i,iill^uw»i^f« .»■HUiMiiMiiMmi .H.imJ.'.'niu» \..wi.'PHi».'-',W»UB,J'H
TABU VI. Total Thermal Characteristic* in "Still" Air of a Tropical Combat Fatigue Enseuble Using the M-l Helmet Liner with Removable Suspension Systmes
Removable Suspension Systems CLO im/CLO lm
Standard HEL Welson-Davie
1.54 0.23 0.36 1.57 0.23 0.36 1.59 0.21 0.34
22
wwiipw '-•■.••wmm'-i", I i, i U»Wpt|pMlUW^IWj||llj!|jg^ i,»wwm» i»JJ»IJIn-i in; n w,^^^»afi ' i'*.MI|l.pS»JiWW.M"('l.|il^
TABLE VII. Thermal Characteristics of Selected Removable M-l HwJMt Llnar Suspension Systems
Air Flow
Suspension Systems w/Helmet Llnar
Standard BEL Welaon-Davis
"Still" Air CLO im/CLO lm
3 Meters/Second CLO im/CLO lm
1.10 0.40 0.44 1.10 0.38 0.42 1.04 0.39 0.41
0.39 0.39 0.38
2.0 C.78 1.8 0.70 1.9 0.72
23
->f- ""■'
Um !i'"'».J.li»l«li aniMni. i». ■ !' " iiiiiii. .,U>WJIII.IHI«I.IIIII»|I i «in ■ ■ i '.PH. ! '■■mm*w~m^-mm*rwm*~* 1 i i. i im i u i.ui.uji. iiiiiuiiminimm n. mmi«,m:W'i " ^ ' " ' '" " ■■■■ I'»"" ■»■■' »m»
Figure 11. Photographs of Helmets with Face Shields: (a; Standard M-l Helmet, Face Shield Up; (b) Standard M-l Helnet, Face Shield Down; (c) Commercial Riot Control Helmet, Face Shield Up; (d) Commercial Riot Control Helmet, Face Shield Down
24
ft- ammm
F.jiii.iii.iii.ww^pwB^wpjpppwWH" jjjuijiiii-w»i"'.)<i»a'i;ui'»i'».<iiiiiiii»*»<wwwijip H'MU n"»wjf'^,j<iu |ii|ijjn,inii.i u..". ijn. ■HJ'umi ,i|»v ^iimiwi' IP,'.M i in!»i,!..i)i,. .Li.11 ■ .'mm
!
TABLE VIII. Thermal Characteristics of the Standard M-l Helmet and a Commercial Riot Control Helmet with a Face Shield in the Up and Down Positions
Air Flow
Headgear
M-l Helmet System w/Face Shield Up
M-l Helmet System w/Face Shield Down
Commercial Riot Helmet u/Face Shield Up
Commercial Riot Helmet w/Face Shield Down
'•««•■Ml" Still" Air 3 Meters/Second
CLO lm/CLO im CLO im/CLO im
1.08 0.43 0.46 0.44 1.9 0.84
1.20 0.38 0.46 0.52 1.7 0.88
1.35 0.38 0.51 0.50 2.0 1.0
1.43 0.33 0.47 0.54 1.5 0.81
25
■pPPimp|||rfP^pF-..IJ«AWWIIii>l .11... I - ■■■' ' iii|iinniM.IU|l»p.'»'mim i Hi -■ nuiUIIPf im» H..I..IU ...i ■ilmiii-.l ■' ■ ■ II I.I..I. |U.i'pi»J»ii .1 HUM!» I II n^
Figure 12. Photographs of Selected Helmets Presented in Table IX: (a) Aircrew AFH-1, (b) Aircrew APH-5, (c) Standard CVC (d) English Infantry.
26
pimiiui uuwuiiimip!!»" '" I ' ■ ..in..... ' ">■» ■■■»" " ■ —-■ . in ■■*■>»"*! um ■ ■■■■■ ii. I ■ n "Mi "i-u 'I» ■«■-' ■■■iii^'ip- ..-..,n«.,^mii#HJiL i|jlllipiipil«iu^!ip
Figure 12 continued, (e) Football Helmet, (f) Experimental Hayes- Stewart, (g) Italian Infantry, (h) Experimental Parachutist Liner.
27
r www ^.i^iWW^W^JIffWiffHPPWW». ^f^ ^*vi«.^WffW«*^**IWl|iW«.i.w<! TTi.'K...Wi"TO''T".W
TABLE IX. Thermal Characteristics of Selected Helmets
Air Flow
"Still1
CLO
1 Air 3 Meters/Second CLO i-n/CLO Helmets lm/CLO im lm
Aircrew AFH-1 1.72 0.38 0.65 0.48 1.8 0.88 Aircrew APH-5 1.45 0.32 0.47 0.51 1.4 0.72 Standard CVC 1.28 0.36 0.46 0.43 1.9 0.83 English Infantry 0.97 0.45 0.44 0.37 1.9 0.70 Football Helmet 1.16 0.32 0.37 0.47 1.6 0.78 Experimental Hayes-Stewart 1.11 0.35 0.39 0.45 1.9 0.87 Italian Infantry 1.03 0.43 0.44 0.42 2.0 0.84 Experimental Parachutist Liner 1.36 0.37 0.50 0.54 1.5 0.81
28
Htjlaiaii ..«MMm
MM II« I II ll|.ill||IW"l'«l|l« II 1 «**JHUU»*BJI., .1. ..!.. r™^-. ^np*n«Kfpni«np»pivmvpimH!m>iiv'■ "^WWBUBUT
3.>
|..h
1111 11 111 11 i i 11 i 11 11 i i 11 i
•STILL" AM
HEAT LOSS MOM HEAD - 2} WATTS
SKIN TEMPERATUR«
32.2° C (LOHBt BOUHDAH)
3J.0* C (UPPER MUNDART)
1 AND 3 AIRCREW AFH-S 2 AMI 4 ITALIA» OR BRUSH V ",
*° __—_____ *° I I 1' I BBÖ/,
0*Y BULB) TCMPCRATUHC *P
}«
1111111 111 1111111111
3 HSTER3/3EC0KB
OUT ei-'LS TEMPEFMTUHE 'C 10 40
11 I I I I I "|- f I I I I HM. IT
HEAT LOSS FROH HaAD • 75 WATTS
SO» TEMPERATURE
32.2% (LOWER BOUHDART)
35.0*C (UPPER BOUNDAÄT)
1 AM) 3 AIRCRIW AP1I-S 2 AUD k ITALIAH OR ENGLISH
i« "0
0<IT BULB TEMPE«4TUKE *F
Figure 13. Graphical Presentation Demonstrating the Combined Effect of Clc and lm/clo Values in Terms of Theoretical Environ- mental Limits for Thermal Equilibrium of the Head for Two Helmets from Table IX: Italian Helmet (One of the Largest lm/clo Values) and the Aircrew APH-5 Helmet (Smallest lm/clo Value); (a) "Still" Air, (b) Air Flow of 3 Meters/Second
29
wi^mn^Ki i in ii ,.». ,j. . . . , ., .„.: . u, 'HF«.«. . i. npi Wjauti- «pup.« 4*4
9. THERMAL CHARACTERISTICS OF SELECTED HELMETS
The helmets shown in the photographs of Figure 12 are of assorted shapes and sizes ranging from snugly-fitting to loose-fitting, from com- paratively rigid suspension systems to flexible suspension systems, and suspension systems fabricated from materials of various moisture perme- abil.ties. From Table IX it is noted that the data for the Aircrew APH-5 heir>t are consistently among the highest clo and lowest im/clo values for the "still" and 3 meters/second air flow conditions. This is mainly because of its very close-fitting design. The English and the Italian infantry helmets consistently show the lowest clo and the highest im/clo values, apparently because of their high proportion of uncovered head surface area. Overall, increasing tne air flow from "still" air to 3 meters/second reduces the clo for all helmets by about 60Z and increases the im/clo by about 4 times the "still" air values. Figure 13a shows a graphical presentation which demonstra as the combined effect of the clo and lm/clo values in "still" air in terms of theoretical environmental limits for thermal equilibrium of the head for men losing 25 watts from the head surface when wearing the Italian helmet (one of the largest im/clo values) and the aircrew APH-5 (smallest lm/clo value). Figure 13b shows the same Information with a 3 meters/second air flow.
10. DISCUSSION AND CL0NCLUSI0NS
It is difficult to determine differences in "still" air in the heat transfer properties of headgear with and without ventilating holes. Although the M-l helmet liner with 10 ventilating holes spaced over the helmet and providing about 8Z of open space in the helmet liner showed an increase in evaporative heat transfer from the head, simply making several holes around the helmet or at the top apparently is of little benefit in increasing the evaporative heat transfer from the head. Removing strips of material from the bottom edge of a helmet, originally covering about 67Z of the head (standoff distance of 1.270 cm.), shows little Improvement in evaporative heat transfer until about 30Z of the helmet material has been removed. For a constant head area coverage of 67Z, the evaporative heat transfer was constant above a standoff distance of 1.270 cm. In wind, ventilating holes appear to Increase the evaporative heat transfer for a snugly-fitting helmet but have negligible effect on all other helmets. Increasing the air flow from "still" air to 3 meters/second reduces the clo for all 8 selected headgear items by about 60Z and Increases the lm/clo by about 4 times the "still" air values.
The surface area affected by a helmet is relatively small compared with
the total body surface area. Any benefit in the heat transfer properties
is more apt to be Improved head comfort rather than n extending physiolog- ical tolerance. A decrease in headgear insulation of 0.1 clc within a
30
MM
wmm•"***•> Jl.i,JMii!UJ|t,fll)»jpiw,ii'iili.ui<''f»li'i-'','l'r''''T« n'"*WW,.*W|l"J'"!"|'i»l|HWP i WrM.'.wwiiaaWWW!W'ywi^!W ■w.*i.."imM."'w»!'P^»''n,»4**njUi'> I.I in if ii. .iimpm«
Insulation range of 1.0 to 1.5 do vlll result in an increase in ccmvective heat transfer fron the head of between 0.4 and 1.0 watts. Increasing the lm/do by 0.1 Increases the evaporative hear transfer from the head by about 2 watts for a vapor pressure difference between the head surface and ambient air of 10 mm Hg. As an example using two different types of headgear the total lm/do of a complete ensemble (tropical combat fatigues, 1 pair of socks, and a pair of black boots) Increases by about 0.02 when the standard West German tankers helmet is replaced by the English helmet. A man exposed to a "still" air environment of 43 C and 20Z relative humidity would have a total heat loss of about 188 watts when wearing the snugly-fltfing, standard West German tankers helmet. Replacing this helmet with an English helmet would increase his heat less to about 203 watts or 15 watts greater. Although these differences in the total heat transfer properties are small, the values obtained for the headgear items studied are measurable and re- producible. Future work on headgear items should consider infantry head- gear in other climates, e.g. tropical and the effect on the heat transfer from the head of using helmets constructed from materials of different thermal conductivities.
31
HP ifi)ag»pipyjGffgwwj»ipc.|pwpi»»^ it»- Lin.„iii»nnmjmw!fi m p— m i M|J| m,n".".uii.»iT..«,»piffl»'w,»'"-"»"'i|.» ■■ -
11. REFERENCES
1. Breckenridge, J.R., "Standard Procedures for Moisture Permeability Index Measurement on Clothing Ensembles", Military Ergonomics Laboratory, USARIEM, Natlck, Mass., March 1967, 4 pp.
2. Coleman, A.E. and A.K. Mortagy, "Ambient head temperature and football helmet design". Med. and Sei in SportJ. 5(3): 204-208, (1973).
3. Edwards, Merrill and Alan C. Burton, "Temperature distribution over the human head, especially in the cold". J. Appl. Physiol. 15(2): 209-211, (1960).
4. Fonseca, G.F., "Heat-Transfer Properties of Ten Underwear-Outerwear Ensembles". Textile Res. J. 40, 553-558 (1970).
i
5. Froes«, 6.J. and A.C. Burton, "Heat Loss from the Human Head". J. Appl. Physiol. 10, 235-241 (1957).
6. Gagge, A.P., Burton, A.C., and Bazect, H.C., "A Practical System of Unite for the Description of the Heat Exchange with his Environment", Science. 94, 428-430 (1941).
7. Levell, CA., Unpublished data, Military Ergonomics Laboratory, USARIEM, Natlck, Mass., (1973).
8. Siple, P.A. In: L.H. Newburgh. Physiology of Heat Regulation and the Science of Clothing, Philadelphia: Saundera, p. 418, (1949).
9. van Green, C.H. and Strydom, N.B., "Temperatur« Changes within Hard Hats as Affected by Ventilation Holes", Int. Z. angew. Physiol. einschl. Arbeltaphyalol.. 26, 283-289 (1968).
10. tfinamann, F.R., "Technical Information on Combat Vahir.le Crewman Helmet", U.S. Army Natlck Laboratories, EPID Study No. 5701, May 24, 1957.
11. Woodcock, A.H., "Moisture Transfer in Textile Systems. Part I", Textile Res. J. 32, 628-633 (1962).
32