Patent Publication Number: US-2021177083-A1

Title: Surgical Personal Protection Apparatus

Description:
RELATIONSHIP TO EARLIER FILED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/208,630 filed 4 Dec. 2018. U.S. patent application Ser. No. 16/208,630 is a continuation of U.S. patent application Ser. No. 15/644,750 filed on 8 Jul. 2017, now U.S. Pat. No. 10,201,207. U.S. patent application Ser. No. 15/644,750 is a divisional of U.S. patent application Ser. No. 14/927,541 filed 30 Oct. 2015 now U.S. Pat. No. 9,706,808. U.S. patent application Ser. No. 14/927,541 is a divisional of U.S. patent application Ser. No. 14/461,480 filed 18 Aug. 2014, now U.S. Pat. No. 9,173,437. U.S. patent application Ser. No. 14/461,480 is a divisional of U.S. patent application Ser. No. 13/616,010 filed 14 Sep. 2012 now U.S. Pat. No. 8,819,869. U.S. patent application Ser. No. 13/616,010 is a divisional of U.S. patent application Ser. No. 12/813,084 filed 10 Jun. 2010, now U.S. Pat. No. 8,282,234. U.S. patent application Ser. No. 12/813,084 is a divisional of U.S. patent application Ser. No. 11/485,783, filed 13 Jul. 2006, now U.S. Pat. No. 7,735,156. U.S. patent application Ser. No. 11/485,783 claims priority under 35 U.S.C. Sec. 119 from U.S. Patent Application No. 60/699,166 filed 14 Jul. 2005. The contents of the priority applications are hereby incorporated by reference. 
    
    
     BACKGROUND 
     Personal protection systems are used in surgical procedures to provide a sterile barrier between the surgical personnel and the patient. One such system is disclosed in U.S. Pat. No. 5,054,480, the contents of which are incorporated herein by reference discloses that basic structure of such a system. Specifically, the traditional system includes a helmet that supports a toga or a hood. This assemblage is worn by medical/surgical personnel that want to establish the sterile barrier. The toga or the hood includes a transparent face shield. The helmet includes a ventilation unit that includes a fan. The ventilation unit draws air through the toga/hood so the air is circulated around the wearer. This reduces both the amount of heat that is trapped within the toga/hood and the CO 2  that builds up in this space. It is further known to mount a light to the helmet. The light, which is directed through face shield illuminates the surgical site. 
     Conventional personal protection systems do a reasonable job of providing a sterile barrier between the surgical personnel and the surrounding environment. However, there are some limitations associated with their use. The toga/hood that covers the wearer blocks sound waves. This means an individual wearing the system may have to speak loudly, even shout, to be heard. This is especially the case when the hooded individual is trying to communicate with another individual similarly attired. 
     Furthermore, while it is known to provide light with the helmet, it has proven difficult to provide a workable light. This is because in one proposed system, it is proposed that the actual light be emitted by a source at a static console. The light is supplied to the helmet for emission therefrom through a fiber optic cable. Thus with this system, the wearer is essentially tethered to the light source. This both limits the mobility of the individual and requires other operating room personnel to navigate around the tether. Alternatively, the light source could be mounted in the helmet. Such light sources generate heat. This heat can cause the temperature beneath the toga/hood to rise to an uncomfortable level. 
     Moreover, the helmet and the equipment it supports, places a load on the head of the wearer. Over time this load can impose an appreciable strain on the muscles and skeletal structure. 
     SUMMARY 
     This invention relates to a new and useful personal protection system such as the type of system used to provide a sterile boundary around medical/surgical personnel. 
     The system of this invention includes a ventilation unit for supplying ventilation air underneath the toga/hood of wearer. There is a light unit. The light unit has a light source positioned in line with the air discharged from the ventilation unit. This arrangement minimizes the buildup of heat around the light unit. 
     The system of this invention also includes an in-helmet mounted RF communications system. 
     The system of this invention also has a head unit that substitutes for a conventional helmet. The head unit includes a head band and a ventilation unit that is suspended above the head band. The ventilation unit is adjustably positioned relative to the head band. This allows the ventilation unit to be positioned relative to the head of the wearer so it is located where it will impose only a minimal strain on the wearer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a perspective view of a helmet type personal protection system of this invention fitted over the head of a user; 
         FIG. 2  is a cross-sectional view of the helmet assembly; 
         FIG. 3  is an exploded perspective view of the helmet assembly; 
         FIG. 3A  is a plan view of the front of the scroll housing; 
         FIG. 3B  is a plan view of the rear of the scroll housing; 
         FIG. 4  is a perspective view of the head band; 
         FIG. 5  is a side view of the helmet assembly with a toga and hood with face shield; 
         FIG. 6  is a perspective view of the helmet assembly illustrating a positioning and supporting system including a mounting clip supporting the face shield via an aperture in the face shield; 
         FIG. 7  is a side view of the helmet assembly implementing a light assembly; 
         FIG. 8  is a bottom view of the helmet assembly implementing the light assembly; 
         FIG. 9  is a back view of the helmet assembly implementing the light assembly; 
         FIG. 10  is a cross-sectional view of the helmet assembly along the line  10 - 10  shown in  FIG. 9 ; 
         FIG. 11  is a bottom view of the helmet assembly implementing the light assembly; 
         FIG. 12  is a cross-sectional side view of the helmet assembly showing a printed circuit board disposed within the helmet assembly; 
         FIG. 13  is a front view of the helmet assembly; 
         FIG. 14  is a side view of the helmet assembly showing a handle for adjusting the angle of the light assembly; 
         FIG. 15  is a side view of the helmet assembly; 
         FIG. 16  is a perspective back view of the helmet assembly along the line  16 - 16  shown in  FIG. 15 ; 
         FIG. 17  is a partial exploded view of the helmet assembly showing the components of an light adjustment mechanism for adjusting the angle of the light assembly; 
         FIG. 18  is a perspective view of the helmet assembly; 
         FIG. 19  is a bottom view of the helmet assembly; 
         FIG. 20  is an electrical block diagram illustrating the flow of electricity from a power supply to a motor and a light source; 
         FIG. 21  is an electrical schematic diagram showing the relationship between electronic components disposed on the circuit board; 
         FIG. 22  is an electrical block diagram of a communications system; 
         FIG. 23  is a side view of the helmet assembly illustrating a microphone of the communications system; 
         FIG. 24  is a front view of the helmet assembly illustrating the microphone and a speaker of the communications system; 
         FIG. 25  is a side view of the helmet assembly illustrating the microphone and the speaker of the communications system; 
         FIG. 26  is a block diagram of how, in some versions of this invention, a single power supply provides the energization current for the fan motor, the light source and the communications transceiver; 
         FIG. 27  is a block diagram of the components internal to a transceiver of this invention; 
         FIG. 28  is a diagrammatic illustration of how signals are exchanged between different communications units of this invention; 
         FIG. 29  is a perspective view of an alternative head unit of the personal protection system of this invention; 
         FIG. 30  is a front view of the head unit; 
         FIG. 31  is a side view of the head unit; 
         FIG. 32  is rear view of the head unit; 
         FIG. 33  is a rear perspective view of the head unit; 
         FIG. 34  is an exploded view of the head unit; 
         FIG. 35  is a perspective view of the face frame; 
         FIG. 36  is a plan view of one of the head straps; 
         FIG. 37  is view of the outside of the rear nozzle assembly shell; 
         FIG. 38  is a view of the inside of the rear assembly shell; 
         FIG. 39  is a perspective view of the inside of the plate of the rear nozzle assembly; 
         FIG. 40  is a perspective view of the knob integral with the rear nozzle assembly; 
         FIG. 41  is a perspective view of tip of the rear nozzle assembly; 
         FIG. 42  is a view of the inside of the lower shell of the ventilation unit; 
         FIG. 43  is a perspective view of the upper shell of the ventilation unit; 
         FIG. 44  is a perspective view of the ventilation unit fan; 
         FIG. 44A  is a perspective view of the underside of the fan. 
         FIG. 45  is a perspective view of the ventilation unit grill unit; 
         FIG. 46  is a perspective view of the ventilation unit motor cover; 
         FIG. 47  is a perspective view of the front nozzle assembly pedestal; 
         FIG. 48  is a perspective view of the front nozzle assembly cap; 
         FIG. 49  is a perspective view illustrating how the light is adjustably mounted to the head unit; 
         FIG. 50  depicts how the flex circuit is attached to the front frame chin bar; 
         FIG. 51  depicts how switches are mounted to the front frame chin bar; 
         FIG. 52  is a plan view of the hood/toga transparent shield used with the head unit; and 
         FIG. 53  is a block diagram of how the power supply, the fan, the transceiver and light generating source of the personal protection system of this invention are contained in a common housing. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     I. Overview 
     Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a personal protection system is generally shown at  10 . 
     The personal protection system  10  is adapted from the personal protection system  10  disclosed in U.S. Pat. No. 6,481,019 to Diaz et al. and U.S. Provisional Patent Application No. 60/664,900, both of which are hereby incorporated by reference. The personal protection system  10  of the present invention is implemented as a helmet assembly  12  mountable to the head  14  of a user, as shown in  FIG. 1 . 
     The personal protection system  10  filters air between the head  14  and body  16  of a user, e.g., a medical professional, and an environment external to the user. The helmet assembly  12  distributes air about the head  14  of the user as will be described below. More specifically, the helmet assembly  12  distributes air toward both a front of the head  14 , i.e., a face of the user, and a back of the head  14 , i.e., a neck of the user. 
     Referring to  FIG. 2 , the helmet assembly  12  includes a shell  17  having an inner shell portion  18  facing the user and an outer shell portion  20  facing away from the user. The outer shell portion  20  is spaced apart from the inner shell portion  18  to define at least one air flow channel  26  between the inner and outer shell portions  18 ,  20 . It is to be understood that the present invention may include more than one discrete air flow channel  26 . The illustrated embodiment includes a single unitary air flow channel  26  and the present invention will be described below in terms of this air flow channel  26 . The shell  17  is preferably formed of acrylonitrile butadiene styrene (ABS), but may be formed, in alternative plastics. 
     The helmet assembly  12  also includes a facial section  40  extending from the shell  17  to define a facial opening  42 . The facial section  40  of the helmet assembly  12  is a chin bar  44 . The chin bar  44  is flexible and is formed of plastic such as polypropylene. The flexibility of the chin bar  44  protects the wearer&#39;s face and absorbs impact when the user contacts an external object with the helmet assembly  12 . The chin bar  44  also holds the hood  92  ( FIG. 1 ) away from the face of the wearer 
     II. Helmet 
     Referring to  FIGS. 2-3 , the helmet assembly  12  includes a fan module  46  mounted in a cavity  38  in the shell  17  Fan module  46  includes a fan  50  and a motor  52  mounted to a scroll housing  48 . Fasteners M that extend through the shell  17  into threaded bores in the housing  48  to hold the module  46  in cavity  38  (housing bores not shown). A cover plate  47  is fixed to the shell  17  below cavity  38  to cover the fan module  46 . A cushion  49  is disposed between the cover plate  47  and a base of the fan module  46 . The cushion  49  absorbs the sound emitted by the fan motor  52 . This reduces the amount of noise emitted by the system  10  of this invention. The scroll housing  48  may be formed of glass-filled polypropylene to reduce vibrations. 
     The helmet assembly  12  further includes an intake grid  100  mounted to the outer shell portion  20 . The intake grid  100  includes a top surface spaced from the outer shell portion  20  of the helmet assembly  12 . The intake grid  100  is contoured to the outer shell portion  20  between the front and rear of the shell  17 . Air is drawn into the scroll housing  48  through the intake grid  100  by the fan  50 . 
     Also shown in  FIG. 3  are various fasteners and washers, not identified, that secure the components forming helmet assembly  12  together. 
     In operation, the motor  52  rotates the fan  50  to draw air into the air inlet  64  of the scroll housing  48  through the intake grid  100 . The air is discharged through two spaced openings in the scroll housing  48 . A first opening  51  seen in  FIG. 3A , is in the front of the scroll housing  48 . The air discharged from opening  51  flows directly into the opening  25  into air flow channel  26 . From channel  26 , the air is discharged from an outlet opening  35  between the inner and outer shell portions  18  and  20 , respectively, in the front of the shell  17   
     The second opening, opening  53 , is located in the rear of the scroll housing  48 , best seen in  FIG. 3B . The air discharged from opening  53  flows into a manifold mounted to the rear of the scroll housing  48 . From the manifold, the air is discharged from two downwardly directed nozzles. The manifold and nozzles are formed as a single unit, S in  FIG. 3 . When the system  10  is worn, the nozzle discharge ports are positioned adjacent the back of the neck of the wearer. 
     The air flow channel  26  defined between the inner and outer shell portions  18 ,  20  terminates at the front section  34  with the front air exits. More specifically, the inner and outer shell portions  18 ,  20  converge toward the front section  34  to define the front air exits. The front air exits may have an air deflector defined between the outer shell portion  20  and the inner shell portion  18  wherein the outer shell portion  20  angles toward the inner shell portion  18  at the front air exits for proper deflection of air toward the front of the head  14  of the user. Such an air deflector is best shown in U.S. Pat. No. 6,481,019 et al., which, again, is hereby incorporated by reference. Air flow channel  26  diverges upon approaching the front air exits. The convergence and divergence of the air flow channel  26  maintains a balanced flow of air about the user&#39;s head  14 . Ultimately, this also has the effect of minimizing or even completely eliminating noise within the helmet assembly  12  due to the air flow. 
     Referring to  FIGS. 2, 3, 4 and 8 , an adjustable head band  128  assists in minimizing the strain on the head  14  and the neck of the user. Strain and torque on the head  14  and neck of the user is minimized by maintaining the weight of the fan  50  and motor  52  over the neck of the user even upon adjustment of the helmet assembly  12  to fit various sized heads  14 . The head band  128  includes a rear support  130  that rigidly extends from the shell  17 . It is understood that the rear support  130  can be a separate part that is connected to the helmet assembly  12  or can be an integral part of the helmet assembly  12 . The rear support  130  includes first and second rigid connectors  132  that connect the rear support  130  to the rear section  36 . In the preferred embodiment, the rear support  130  is connected to and extends from the rear section  36  of the inner shell portion  18  and will be described below in terms of the inner shell portion  18 . However, it is to be understood that the rear support  130  can connect to and extend from any portion of the shell  17 . 
     An adjustment segment  134  having a first side  136  and a second side  138  is also part of head band  128 . Although not required, the rear support  130  preferably includes the adjustment segment  134 . In the preferred embodiment, the adjustment segment  134  is integral to, or the same part as, the rear support  130 . In alternative embodiments, the adjustment segment  134  is a discrete component that is simply mounted to the rear support  130 . In either situation, the adjustment segment  134  defines apertures  140  for receiving a first end  144  and a second end  146  of a strap  142  flexibly connected to and extending from the front section  34  of the inner shell portion  18 . The first end  144  is disposed within the first side  136  of the adjustment segment  134 , and the second end  146  is disposed within the second side  138  of the adjustment segment  134 . Preferably, the first end  144  is movably disposed within the first side  136  of the adjustment segment  134 , and preferably the second end  146  is movably disposed within the second side  138  of the adjustment segment  134 . However, as will be understood from the explanation below, the first end  144  may be movably disposed within the first side  136  of the adjustment segment  134  and the second end  146  may be fixedly disposed within the second side  138  of the adjustment segment  134 . Alternatively, the first end  144  may be fixedly disposed within the first side  136  of the adjustment segment  134  and the second end  146  may be movably disposed within the second side  138  of the adjustment segment  134 . 
     The strap  142  further includes a frontal portion  148  disposed between its first and second ends  144 ,  146  and opposite the adjustment segment  134  of the rear support  130 . At least one support arm  150  flexibly extends from the frontal portion  148  of the strap  142  to flexibly connect the strap  142  to the front section  34  of the inner shell portion  18 . These support arms  150  act as hinges for the head  14  support assembly. Preferably, there are two support arms  150  that extend from the frontal portion  148  of the strap  142 . In such a case, the two supports arms are connected to the front section  34  of the inner shell portion  18  and to the frontal portion  148  of the strap  142  equidistant from one another. A gap  152  exists between the frontal portion  148  of the strap  142  and the front section  34  of the inner shell portion  18 . 
     III. Toga and Hood 
     Referring to  FIG. 5 , the personal protection system  10  includes a toga  88  having a body portion  90  for covering substantially all of the body  16 . Toga  92  includes a hood  92  for covering the head and helmet assembly  12 . The body portion  90  can extend downward to cover any portion of the body  16  of the user. For instance, the body portion  90  can extend downward to the waist of the user, or to the ankles of the user. The hood  92  includes a filter element  94  to filter air between the user and the external environment. The facial section  40  of the helmet assembly  12 , introduced above, also operates to maintain the hood  92  away from the head  14  of the user. The intake grid  100  spaces the filter medium  94  out away from the outer shell portion  20  and the fan  50 . 
     As is known in the art, a hood unit may be offered as a covering separate from the complete toga. This type of hood unit is used when there is only a need to provide a barrier around the head of the wearer. 
     A transparent face shield  96  permits the user to view through the hood  92 . The face shield  96  may include anti-reflective and/or anti-refractive coatings to enhance vision through the face shield  96 . As shown in  FIG. 5 , the face shield  96  is mounted to the hood  92  such that the face shield  96  covers the facial section  40  and the facial opening  42  of the helmet assembly  12  once the user dresses into the personal protection system  10 . The face shield  96  is sewn into the hood  92 . The facial opening  42  of the helmet assembly  12  receives the face shield  96 . In this version of the invention, facial section  40  of the helmet assembly  12  includes a hook-and-loop fastener  98  to further facilitate attachment of the face shield  96  to the facial section  40  for covering the facial opening  42 . 
     IV. Light Assembly and Fan Assembly 
     As shown in  FIG. 3  and  FIGS. 7-19 , the personal protection system  10  includes a light assembly  200 . The light assembly  200  is disposed within the hood  92  behind the face shield  96  to emit a beam of light that projects outside of the hood  92 . Since the light assembly is disposed within the hood  92 , there is no need to meticulously clean the light assembly to keep it to the sterile conditions of a surgical room. Light assembly  200  includes a light generating unit, light source  201 , disposed adjacent to a lens (not shown). 
     The light source is preferably one or more light-emitting diodes (LEDs). The LED emits white light. In one version of the invention, light is emitted at a color temperature of 5500° K. Light in this spectrum is equivalent to daylight and provides true tissue color rendition. A light housing  202  supports and surrounds the LEDs and the lens. One suitable light assembly  200  is the PeriLux LED, manufactured by PeriOptix, Inc. of Mission Viejo, Calif. The light source may alternatively be an incandescent light bulb or other suitable sources as are well known in the art. One possible alternative is the use of a light source mounted somewhere on the user and fiber-optic cables to carry the light to the light housing. 
     The lens is circular in shape. In some versions of the invention, the longitudinal position of the lens relative to the light source  201  is selectively set. This allows the user to selectively focus/diffuse the beam of light emitted from the light assembly  200 . Many lens displacement assemblies include a rotating collar. Rotating the collar in a first direction cause movement of the lens to focus light is concentrated in a small area. Rotation of the collar in the opposite direction results in movement of the lens so that the emitted light is diffused about a large area. This rotation of the collar may be done manually or with a focusing servo motor. Control of the electric servo motor is explained in greater detail below. 
     Light assembly  200  includes a light angle adjustment mechanism  204 . Mechanism  204  allows the user to change the direction of the beam of light so it can be directed to a specific location. Specifically, the light housing  202  is pivotally mounted to two parallel legs  210  (one shown in  FIG. 7 ). Legs  210  are integrally formed with and extend downwardly from a rigid block  209 . Block  209  is attached to the front outer surface of the strap  142 . A pin  211  that extends through the ends of the legs  210  pivotally holds the light housing  202  to the legs. 
     A semi-rigid cable  216  regulates the pivotal movement of the light housing  202 . The cable  216  is contained in a sheath (not identified). A cable clamp AW and rivet P cooperate to hold the forward end of the sheath to the exposed face of the inner shell portion  18 . The rear end of the sheath, with the cable  216  contained therein, extends through an opening in the shell  17  into the void space between the inner and outer shell portions  18  and  20 , respectively. A ring clamp AZ is disposed over the front of the housing, immediately proximal to the front face. The opposed ends of the ring clamp (one shown as element  206  in  FIG. 8 ) extend upwardly towards shell  17 . An elongated screw  217  ( FIG. 3 ) extends between ring clamp ends  206  to compression secure the ring clamp AZ to the light housing  202 . The front end of the cable  216  is wrapped around the exposed section of screw BA between the ring clamp end sections  206 . 
     As seen in  FIG. 10 , a lever arm  214  disposed inside shell  17 , selectively extends and retracts the cable  216 . Lever arm  214  is connected by a pin (not identified) to an adjustment knob  212  located outside of the shell  17  ( FIG. 9 ). The pin extends through the shell outer portion. The proximal end, the rear end of the cable  216  is attached to the end of the lever arm  214  distal from the pin. The rotation of the knob and lever arm sub-assembly thus results in the extension/retraction of the cable. The cable movement, in turn pivots the light housing  202  around the axis defined by pin  211 . 
     The light housing  202  and, more particularly, the light source  201 , are positioned directly under the front air outlet opening  35 . By positioning as such, the air discharged from opening  35  blows the warm air surrounding the light assembly  200  away from the light assembly. This reduces the buildup of heated air adjacent the light assembly. Instead, the heated air is exhausted out of the hood  92 . The removal of this heated air lessens the extent to which the heat generated by the light assembly excessively warms the wearer of the personal protection system  10 . 
     Still another feature of this construction of the invention is that it minimizes the extent to which the temperature of the light assembly  200  itself rises due to the heat emitted by source  201 . By maintaining the light source  201  at a relatively low temperature, the source itself is able to function as a relatively efficient light emitter. (The light-emitting efficiency of LED type light source drops with an increase in the temperature of the LED.) 
     Referring now to  FIG. 20 , the control circuit for motor  52  and light source  201  are shown in block form. Power supply  70  energizes both the motor and the light source. In alternative versions of the invention, power supply  70  may be divided into a pair of power supplies, with each power supply individually powering the motor  52  or the light assembly  200 . 
     Power supply  70  is preferably at least one cell (i.e., battery). The at least one cell may be rechargeable. However, non-rechargeable (i.e., disposable) cells may also be used. In one version of the invention, power supply  70  provides a 6 VDC power signal. However, other voltages may alternatively be implemented. 
     The first power supply  70  is preferably mounted to the body  16  of the user as shown in  FIG. 5 . By mounting the first power supply  70  outside of the toga  88 , it can be easily replaced (i.e., switched out) during a medical/surgical procedure. In some versions of the invention, power supply  70  is located where it is accessible through the toga. Alternatively, the first power supply  70  may be disposed within, i.e., integrated into, the helmet assembly  12 . 
     Referring again to  FIG. 21 , the personal protection system  10  further includes a fan control circuit  224  for regulating the actuation of the fan motor  52 . A voltage regulator  220  applies a constant voltage signal to control circuit  224  for energizing the control circuit. Voltage regulator  220  regulates the 6 VDC electric current received from the power supply. In one version of the invention, voltage regulator  220  provides a 3.3 VDC electric current which energizes the fan control circuit  224 . 
     A light control circuit selectively applies an energization signal to the light source  201  to control both the on/off state of the light source and the intensity of the light emitted by the source. In  FIG. 21 , the light control circuit is shown as current regulator  230 . The current regulator  230  receives a constant voltage energization signal from a voltage regulator  222 . In one version of the invention, voltage regulator  222 , which is connected to power supply  70 , supplies a 3.6 VDC signal to current regulator  230 . 
     In some versions of the invention a single voltage regulator provides a common constant voltage to both the fan control circuit and the light control circuit. In some versions of the invention, there may not even be a need to provide a voltage regulated energization signal to either the fan control circuit or the light control circuit. Thus, in some versions of the invention, either one or both of the fan and light control circuits are powered directly from the power supply  70 . 
     The fan control circuit  224  is electrically connected to the fan motor voltage regulator  220  and the motor  52 . The fan control circuit  224  receives electric current from the fan motor voltage regulator  220  and conditions the electric current to control the speed of the motor  52  and the fan  50 . 
     In the illustrated version of the invention, the fan control circuit  224  provides implements pulse-width modulation (PWM) for controlling the speed of the motor  52  and the fan  50 . To accomplish the PWM, the fan control circuit  224  includes a microcontroller  118  and a power transistor  226 . The microcontroller  118  includes a plurality of inputs and outputs. Two switches  120  and  122  are pushbuttons are electrically connected to individual inputs of the microcontroller  118 . (Not identified are the pull up resistors associated with the switches.) The user presses the pushbuttons to adjust the desired speed of the fan  50  (and the consequential air flow). The switches are in the form of pushbuttons mounted to the side of the helmet assembly  12  and are easily operable by the user through the hood  92 . 
     At least one output of the microcontroller  118  is electrically connected to the power transistor  226  to selectively turn on and turn off the transistor based on the desired speed of the fan  50 . More specifically, the energization signal applied through the transistor is a PWM signal having a constant frequency and a variable on duty cycle that is directly proportional to the desired fan speed. 
     Power transistor  226  is in one version of the invention, actually a pair of power MOSFETs, the individual MOSFETs not shown. Here a primary MOSFET is a P-channel type and a secondary MOSFET is an N-channel type. The drain of the primary MOSFET is tied to the positive input of the power supply. The source of the primary MOSFET is tied to fan motor  52 . The gate of the primary MOSFET is tied to the positive terminal of the battery through a resistor. The drain of the secondary MOSFET is also tied to the gate of the primary MOSFET. The source of the secondary MOSFET is tied to ground. The gate of the secondary MOSFET is connected to a control line from the microcontroller  118 . Thus, the signal present at the drain of the secondary MOSFET gates the primary MOSFET. The IRF7307TR Power MOSFET manufactured by International Rectifier, headquartered in El Segundo, Calif. is a single package that contains both the P- and N-channel MOSFETs that collectively form power transistor  226 . Of course, those skilled in the art realize other possible implementations of the power transistor  226  are possible. 
     Microcontroller  118  is preferably is a Model ATmega8 manufactured by Atmel Corporation, headquartered in San Jose, Calif. The ATmega8 includes built-in PWM support. Other suitable microcontrollers  118  or microprocessors are evident to those skilled in the art. The microcontroller  118  may also be used for functions separate from controlling the speed of the fan  50 , as is described in greater detail below. 
     In one version of the invention, the current through motor  52  is used as feedback signal to establish the PWM rate. A resistor (not illustrated) is tied between the motor  52  and ground. The voltage across the resistor is applied to microcontroller  118  so as to serve as an indication on the motor speed. Motor speed is adjusted by varying the percent on duty cycle of the pulse per fixed total period (on and off) of the pulse. 
     Microcontroller  118  may also be electrically connected to the focusing servo motor and the light angle servo motor. This eliminates the need to hand adjust the light. 
     In addition to controlling the volume of air flowing into the helmet assembly  12 , the invention provides an audible indication of when the fan is at the minimum and a maximum air flow rates. This indication is provided by momentarily resetting the frequency of the PWM signal applied to the motor. This in turn, causes the motor to be actuated at a rate that causes is shaft to rotate in a manner that causes sound detectable by the human ear to be emitted. This sound provides an audible indication of the minimum and the maximum volume of air to the user. That is, the present invention provides the user with an audible ‘ping’ upon reaching the minimum and maximum volumes of air flowing into the helmet assembly  12 . 
     This ping is also provided each time the control circuit  224 , in response to the depression of one of the control buttons, raises or lowers the speed of the fan motor  52 . At the opposed high and low ends of the motor speeds, the controller is configured to actuate the motor so two closely spaced apart in time pings are emitted at the same frequency. This provides the user notice the maximum or minimum motor speed setting has been reached. 
     The audible ping is provided by, for a brief period, for example between 0.1 and 0.2 seconds, running the fan motor at a frequency at which the motor generates an audible sound. For example, during normal actuation of the motor, the constant frequency of the energization signal applied by the control circuit  224  is 30.3 kHz. Between the transition from outputting the energization signal at a first duty cycle to a second duty cycle, (in order to change the speed of the motor), the energization pulses are applied to the motor at a frequency of between 261 to 523 Hz at a 50% duty cycle. As a result of the energization pulses being applied at this frequency, the speed of the motor drops appreciably. This causes the motor  52  to emit a tone detectable by the human ear 
     In some versions of the invention, the frequency at which the motor is actuated in order to generate the ping varies with new speed range the motor is being set to operate at. For example, in one embodiment of this version of the invention, prior to each time the control circuit  224  increases the on duty cycle of the motor energization signal in order to increase motor speed, the control circuit first applies a high frequency ping-generating energization signal. This results in a relative high frequency ping signal being generated. Prior to the control circuit  224  decreasing the on duty cycle for the energization signal in order to decrease motor speed, the control circuit applies a lower frequency ping-generating energization signal. This results in the emission of a lower frequency ping from the motor  52 . Thus, the surgical personnel not only receive an audible indication the fan speed is being reset, they receive an indication regarding if the speed is being lowered or increased. 
     However, it is to be understood that the frequency at which the motor is selectively actuated may otherwise be within the acceptable range of unaided human hearing (30 Hz to 20 kHz) so long as it provides the audible indication. The frequency of the activation rate causes various components of the motor  52  of the fan module  46  to vibrate at the frequency thereby generating the audible indication. 
     Alternatively, the fan control circuit  224  includes a potentiometer, also commonly referred to as a variable resistor or varistor, to control the speed of the motor  52  and fan  50 , instead of utilizing PWM. Additional implementations for varying the speed of the motor  52  and fan  50  are known to those skilled in the art and may be alternatively utilized. 
     A printed circuit board  228  (PCB) is disposed within the helmet assembly  12 . The PCB  228  supports the voltage regulators  220 ,  222 , the microcontroller  118 , and associated electronic devices. The PCB  228  includes conductive tracks to electrically connect items mounted on the PCB  228 , as is well known to those skilled in the art. 
     The personal protection system  10  also includes a light current regulator  230  for providing a constant current, regardless of voltage, to the light source. By keeping the current constant, the light source provides a steady illumination that does not degrade as the cells of the first power supply  70  drain and lose voltage. The light current regulator  230  is preferably integrated with the light assembly  200  within the light housing. However, the light current regulator  230  may be disposed on the PCB  228 . 
     The personal protection system  10  also includes a low power detection circuit for alerting the user when the cells of power supply  70  are running low. In the preferred embodiment, a voltage divider circuit  232  comprising a pair of resistors is electrically connected to the first power supply  70 . The signal present at the junction of the resistors is applied as an input signal to microcontroller  118 . An enunciator  234  is electrically connected to one of the outputs of the microcontroller  118 . The enunciator  234  may be an indicating LED, preferably mounted within the helmet assembly  12  and within the field of view of the user. The enunciator  234  may also be a loudspeaker for producing an audible signal that is hearable by the user, or a combination of the loudspeaker and LED. Alternatively, the enunciator  234  may be substituted with selectively activating and deactivating the power transistor  226  to vibrate the fan and generate an audible signal, as described above. 
     V. Communications Unit 
     Referring to  FIGS. 22-27 , personal protection system  10  also includes a communications unit  236 . The communications unit  236  provides wireless communication between other communications units  236 . The other communication units may be integrated with other personal protection systems  10  or embodied as one or more stand-alone units. The communications units  236  allow for convenient voice communications between the users of the personal protection systems  10 . 
     The communications unit  236  includes a microphone  238 , a speaker  240 , and a transceiver  242 . Communications unit  236  also includes a second power supply  244 . The second power supply  244  powers transceiver  242 . Second power supply  244  is preferably at least one cell. The at least one cell is preferably rechargeable; however, non-rechargeable cells may also be used. The at least one cell may be a single cell or a plurality of cells connected together. The transceiver  242  and second power supply  244  are often packaged together and mountable on the body  16  of the user. 
     Alternatively, as seen in  FIG. 26 , the transceiver  242  is electrically connected to the first power supply  70 , such that the user would not have to carry multiple power supplies. In these versions of the invention a third voltage regulator  241  provides a third constant voltage signal to the transceiver  242 . This third voltage is different from the regulated voltages provided to the fan control circuit  224  and the light control circuit (current regulator  230 ). Transceiver  242  may also be alternatively disposed within the helmet assembly  12 . 
     Microphone  238  converts speech into electrical signals. The signals produced by the microphone  238  are applied to the transceiver  242 . Transceiver  242  is preferably a radio frequency (RF) transceiver  242  capable of transmitting and receiving RF signals. The transceiver  242  converts the electrical signal into an RF signal and transmits the RF signal. The transmitted RF signal may then be received by the transceivers  242  of the other communication units. The transceiver  242  converts the received RF signal into an electrical signal. The speaker  240  is electrically connected to the transceiver  242  and receives the electrical signal from the transceiver  242 . The speaker  240  decodes the electrical signal into an audio wave which can be heard by the user. 
     Microphone  238  is attached to the chin bar  44  of the helmet assembly  12 . A cable  239  (shown in phantom) over which the signals produced by the microphone is similarly disposed in the chin bar  44 . The microphone may be mounted to other locations on the helmet. 
     In one version of the invention, speaker  240  is an earpiece. The earpiece includes a hook shaped to be worn on the ear of the user. A bud with the actual sound generating transducer is attached to the hook. The bud is shaped to be positioned adjacent or in the ear canal of the user. The audio signal cable that supply signals to the bud are mounted to the helmet. The front end of the cable is however, not mounted to the helmet. This provides a degree of flexibility between the earpiece and the helmet shell  17 . This flexibility accommodates for differences in body size of individual users. This flexibility also allows the user to move his/her head while using the personal protection system  10  of the invention while the earpiece remains in place. Also, multiple mounting assemblies are provided in the helmet. This allows the earpiece to be mounted for insertion in either ear of the user of the system  10 . 
     Transceivers  242 , in one version of the invention, operate in the 900 MHz band. The individual transceivers exchange digital, spread spectrum RF signals. The communications units  236  preferably operate in full duplex, i.e., the transceivers  242  can transmit and receive RF signals at the same time. One example of a suitable transceiver  242  is the STx 1000 manufactured by Eartec of Narragansett, R.I. Coachcomm of Auburn, Ala. also markets an appropriate transceiver system. Each of these systems allows three or more individuals to simultaneously use the surgical protect system  10  of this invention and communicate in full duplex mode with each other using the transceivers. There is no need to depress a push-to-talk switch in order for any individual to communicate with another individual. Thus, this protection system  10  allows a group of individuals (three or more) to engage in conversation with each other as if in normal group conversation, without having to raise their voices in order to overcome the sound attenuating of the protective hoods  92  and the noise generated by the fan  50  and motor  52 . 
       FIG. 27  illustrates in block form an alternative transceiver  242   a  of this invention. Transceiver  242   a  includes a modulator  252  for converting audio signals received from the microphone  238  into RF signals. The RF signals generated by the modulator  252  are broadcast over communications unit antenna  237 . Also connected to antenna  237  is the transceiver demodulator  254 . The demodulator  254  converts the received RF signals into audio signals that can be used to actuate the speaker  240 . 
     Actuation of the modulator  252  and demodulator  254  is controlled by a transceiver controller  256  also part of transceiver  242   a . This transceiver controller  256  could be a conventional digital microprocessor, a PLA or a DSP. Transceiver controller  256  regulates the actuation of the modulator  252  and demodulator  254  in part based on the state of three user actuated switches  258 ,  260  and  262 . An individual wearing system  10  of this invention could actuate one switch, for example switch  258 , in order to effectively “turn off” the demodulator.  254 . An individual takes this step if he/she does not want to receive the transmissions broadcast by others employing the communications units. If the individual wants the transceiver  242   a  in this state, the transmitter controller could respond by deactivating the demodulator  254 . Alternatively, the transceiver controller  256 , in response to the user wanting speaker  240  deactivated, turns on a FET that causes the audio output signal generated by the demodulator  254  to go to ground (FET not illustrated). 
     Transceiver controller  256  also selectively deactivates the output of RF signals by the modulator  252 . The individual using system  10  may want the modulator  252  to temporarily stop broadcasting RF signals with embedded audio signals if he/she wants to conduct a conversation with a nearby individual that is not for broadcast. Switch  260  is actuated to regulate the selective broadcast of the RF modulated audio signals. In response to the individual wanting the transceiver  242   a  to not broadcast audio signals, the transceiver controller  256  temporarily stops actuation of the modulator  252 . Alternatively, by switching a FET (not illustrated) the transceiver controller  256  selectively blocks the forwarding of audio signals from the microphone to the modulator  252 . 
     The transceiver controller  256  also regulates the modulator  252  to control which group or groups of other communication units  236  are able to receive signals emitted by the transceiver  242   a . For example, in versions of the invention wherein the individual transceivers exchange signals using a direct sequence spread spectrum protocol, the transmitter controller  256  regulates the codes used to establish the modulation of the output signals and the demodulation of the input signals. In versions of the invention wherein the individual transceivers exchange signals using a frequency hopping spread spectrum protocol, transceiver controller  256  generates the code that establishes the frequency hopping pattern of the carrier frequency. Switch  262  is the control member that is actuated to establish which group or group of communications units are able to exchange and/or receive signals. 
     The utility of the protection system of this invention&#39;s ability to selective exchange signals is now explained by reference to  FIG. 28 . Here, five individual communication units  236   a - 236   e  are shown. Arbitrarily, communications unit  236   d  is one unit that has this selective transmission/reception capability. Thus, by depressing switch  262 , the associated transmitter controller  256  configures the transceiver  242   a  of communication unit  236   d  so that the broadcast audio signals can be received by all the remaining units  236   a ,  236   b ,  236   c  and  236   e  or just by unit  236   e . This allows a surgeon to have some privacy to communication with another individual wearing the system  10 . Alternatively, this allows a surgical assistant to communicate with another individual without disturbing the surgeon. 
     In  FIG. 29 , a receiver  264  is also shown. The receiver is capable of receiving the signals broadcast by one or more the communication units  236   a - 236   e . The audio signals broadcast by the receiver  264  can be broadcast through a loudspeaker  263 . This may be desirable in a teaching setting. Alternatively, the audio signals may be stored with the aid of a recorder  265 . Again, by selective modulation of the broadcast signals, the ability of the receiver to demodulate the signals broadcast by any particular transceiver  242   a  is selectively regulated. 
     Returning to  FIG. 28 , it is seen that a unit processor  272  is connected to the transceiver controller  256 . Digital signals extracted from the received RF signals by the demodulator  254  are forwarded to the transceiver controller  256 . Modulator  252  is able to embed digital signals received from the transceiver controller  256  into the broadcast RF signals. Primarily the transceiver controller  256  functions as an intermediate processor for transmitting digital signals received by the unit processor  272  and forwarding digital signals used by the unit processor. In some versions of the invention, transceiver controller  256  and unit processor  272  are a single unit. 
     The digital RF signals are exchanged with a static RF transceiver  259  seen in  FIG. 28 . Transceiver  259  is connected to a communications bus  266  in the operating room. Other units connected to the bus include the below-discussed operating room control head  261  and equipment such as a personal computer  268 . One such operating room control head  261  is sold by the Applicants&#39; Assignee under the trademark SIDNE. This arrangement allows the transceiver  242   a  to serve as the unit through which other components of the surgical protection system  10  exchange signals with remote devices. In  FIG. 28 , the operating room control head is shown as receiving audio signals from the static receiver  264 . In some versions of the invention, transceivers  264  and  259  are a single unit. 
     For example, by speaking into the microphone  238 , the surgeon speaks the command “Focus Light”. The audio signal representative of these words is transmitted by transceiver  242   a  to the operating room control head. The operating room control head processes the audio signals to decode the command. Once the command is interpreted, the operating room control head, through transceiver  259  generates a command data packet to the transceiver  242   a . The transceiver  242   a  strips out the command message and forwards it to the unit processor  272 . Unit processor  272 , upon receipt of the command, generates appropriate control signals to cause the actuation of the servo motor employed to displace the lens integral with the light assembly  200 . 
     The speed of the fan motor  52  is similarly regulated by the integrated system of this invention. 
     Communication unit  236   a  can also provide voice actuated control of the other equipment in the operating room such as the surgical instruments and the operating room environmental settings (HVAC and light). More specifically, the spoken commands entered through microphone  238  are transmitted by transceiver  242   a  and receiver  264  to the operating room control head  261 . The operating room control head then generates the appropriate instruction packets that are output on bus  266  to the appropriate device that is to act on the instructions. 
     The integrated construction of the system of this invention also allows the personal protection system  10  to report back information regarding its own operating state. In  FIG. 28 , the signal present at the junction of the two resistors forming voltage divider  232  is shown as being applied to unit processor  272 . In the event the signal present at this point falls to a level at which indicates the charge stored in power supply  70  is becoming low, the unit processor  272  generates a data packet with these data. The data packet is forwarded to the transceiver controller  256  so it is broadcast by the transceiver  242   a . The data packet is received by transceiver  259 . This packet is forwarded to the personal computer  268 . This provides personnel in the operating room with notice that the particular power supply  70  worn by a specific individual is close to being discharged and should be replaced. 
     VI. Alternative Head Unit 
       FIGS. 29 through 34  illustrate an alternative support structure for supporting hood  92  around the head and upper body of the wearer. This particular support structure is a head unit  270 . Head unit  270  includes a head band  272  to which a ventilation unit  274  and light  276  ( FIG. 49 ) are adjustably mounted. The air forced through the ventilation unit  274  is discharged through front and rear nozzle assemblies  280  and  282 , respectively. The adjustability of the ventilation unit  274  relative to the head band allows the components forming the unit, primarily the ventilation fan  278 , to be positioned relative to the body of the wearer where the physical strain the unit imposes on the wearer is minimized. 
     More particularly, head unit  270  includes a face frame  286  formed of plastic that has some flexibility. In one version of the invention, face frame  286  is formed from polypropylene or Nylon. Face frame  286 , best seen in  FIG. 35 , is shaped to have a forehead band  288  that has a curvature designed to allow the bar to fit against the forehead of the individual. Not shown are padding that may be secured to the inner surface of the forehead band  288 . Extending downwardly from the opposed ends of forehead band  288 , face frame  286  has downwardly extending support posts  290 . A chin bar  292 , also part of face frame  286  extends between the opposed bottom ends of support posts  290 . Chin bar  292  has a curved shape such that forward portion of the guard between the posts  290  extends forward of the posts. 
     Also part of face frame  286  is a support strap  294 . Support strap  294  is in the form of a generally rectangular strip and extends upwardly from the center of the forehead band  288 . As discussed below, support strap  294  is the member from which the ventilation unit  274 , light  276  and front nozzle assembly  280  are suspended. 
     A mounting pin  296  extends outwardly from each of the face frame support posts  290 . Each mounting pin  296  has a stem (not identified) that extends outwardly from the outer surface of the associated support post  290 . Each mounting pin  296  also has a wide diameter head  298  that forms the free end of the pin. Mounting pins  296  support and secure the transparent shield integral with the hood. 
     A head strap  302  extends rearwardly from each end of the face frame forehead band  288 . Collectively, the forehead band  288  and head straps  302  form the head band  272 . Head straps  302  are formed from very flexible plastic such as Nylon 66. Each head strap  302 , as seen in  FIG. 36 , includes a base  306  that has a relatively wide width. Base  306  is seated against the inner surface of the associated end of the forehead band  288 . Two openings  308  extend through each strap base  306 . Openings  308  accommodate fasteners (not illustrated) that hold the head strap  304  to the face frame  286 . In the illustrated versions of the invention, a counterbore (not identified) extends around each opening  308 . 
     A leg  310  extends downwardly from each head strap base  306 . Each leg  310  has a width less than that of base  306  from which the leg extends. Each head strap  302  has a rack  312  that extends from the free end of the leg  310 . The racks have a set of teeth (not identified) that extend laterally away from the longitudinal axis of the rack.  FIG. 36  illustrates the head strap  302  for the left side of head unit  270 . This head strap  302  is formed so that the rack teeth project downwardly. The head strap  302  for the right side of the head unit  270  is formed so that the teeth project upwardly. A toe  314  projects perpendicularly away from the free end of each rack  312 . Each toe  314  is directed in the same direction in which the associated rack teeth are directed. 
     Rear nozzle assembly  282  both directs the output flow from the fan  278  down the neck of the wearer and holds head straps  302  together. Rear nozzle assembly  282  includes a shell  320  and a tip  318  that rotates around the longitudinal axis of the shell. 
     The rear nozzle assembly shell  320  now described by reference to  FIGS. 37 and 38 . Shell  320 , is formed from a single piece of plastic and has a three-sided trunk  322  from which two wings  324  extend. More particularly, the trunk  322  is formed to have a back wall  326  that curves into two opposed side walls  328 . Shell  320  is further formed so that the opposed side walls  328  are inwardly tapered. Consequently, shell  320  is wider at the top than at the bottom. The shell  320  is further formed to have two spaced apart ribs  330  and  332  that extend laterally across the inner surface of the shell, from side wall to side wall. Rib  330  is located around the open end of the shell  320 . Rib  332  is parallel to and located below rib  330 . 
     A plate  334  extends from the inner surfaces of back wall  326  and side walls  328 . Plate  334  extends to and does not project beyond the inner edges of the side walls  328 . An opening  336  extends through the plate  334 . Opening  336  is centered along an axis that extends longitudinally through the void space defined by the shell back wall  326  and side walls  328 . 
     A rigid tubular sleeve  340  extends inwardly from the shell back wall  326  so to project into the void space between the back wall and side walls  328 . Sleeve  340  extends from an opening  342  in the back wall  326 . The back wall  326  is further formed to have an annular ring  344  concentric from and radially spaced away from opening  342  that projects from the wall outer surface. Ring  344  is formed with spaced apart teeth  346  that extend inwardly to opening  342 . 
     Each shell wing  324  extends from a separate one of the base side walls  328 . The wings  324  are basically three wall structures that are arranged so that the open faces thereof extend forwardly, toward face frame  286 . Plural spaced apart reinforcing webs  350  extend through the void spaces defined by each wing  324  and the trunk side wall  328  from which the wing extends. Webs  350  extend laterally, that is perpendicular to the top-to-bottom longitudinal axis through the shell  320 . 
     A plate  352 , also part of the rear nozzle assembly  282 , extends over the open void defined by the shell  320 . Plate  352 , now described by reference to  FIG. 39 , has a panel section  354  with a generally concavo-convex profile. The panel section  354  is further formed to have side edges (not identified) that are inwardly tapered. Panel section  354  is further formed so that the opposed top and bottom side edges are outwardly bowed. The panel section  354  is also shaped to have curved corners. 
     Extending outwardly from the inner surface of the panel section  354 , the surface seen in  FIG. 39 , plate  352  is shaped to have two four sided reinforcing frames  356 . Each reinforcing frame  356  extends outwardly from the inner surface of panel section  354 . Each frame  356  has two parallel and spaced apart top and bottom ribs  358 . An outer rib  360  located along the adjacent side edge of the panel section  354  extends between ribs  358  at one end of each frame. An inner rib  362 , that is curved toward the side, extends between each of the ribs at the opposed inner end of each frame  356 . 
     A hole  364  extends through the center of panel section  354 . The panel section  354  is formed with an annular rib  366  around the hole  364 . The plate  352  is further shaped so that the frame inner ribs  362  have a center of curvature that is concentric with hole  364 . 
     A foot  368  projects outwardly from the bottom of panel section  354 . Foot  368  has a planar base  369  that forms the bottommost structural component of the plate  352 . Steps  370  extend from the opposed ends of foot  369  to the adjacent sections of the panel section bottom edge. Short lips  372  extend from each step  370  a short distance along the adjacent section of the panel section bottom edge. A reinforcing web  374  extends along the inner surface of the panel section  354 . Web  374  extends between the opposed free ends of lips  372 . The web  374  is parallel with and spaced apart from the two linearly aligned bottom ribs  358  of the reinforcing frames  356 . Thus, a slot  359  is defined between the lowermost ribs  356  and web  374 . 
     The plate  352  also has a three sided collar  378  that is integral with and extends a short distance above the panel section  354 . Collar  378  has a front wall  380 . Two side walls  382  curve inwardly from the opposed ends of the front wall  380 . Formed integrally with the collar are two parallel ribs  384  and  386 . Rib  384  extends inwardly across the coplanar top edges of the collar front wall  380  and side walls  382 . Rib  386  is located below and is spaced from rib  384 . 
     A lip  387  extends from each collar outwardly along the panel section top edge. The lips  387  project away from the inner surface of the panel section  354 . A web  390  extends outwardly from the inner surface of the panel section  354  between the ends of the opposed lips  387 . The web  390  is parallel to and located above the opposed, linearly aligned top ribs  378  of the reinforcing frames  356 . Thus, a slot  392  is defined by the top located ribs  356  and web  390 . 
     Plate  352  is further formed to have a support arch  394 . The arch  394 , which has a generally circular shape, extends upwardly from top edge of panel section  354 . While cross sectional slices through the arch are of constant diameter, the arch does not lie flat. The arch  394  is angled toward the center. This profile approximately matches the general contour at the back of the skull. More particularly, the opposed terminuses of arch  394  are each located between one end of collar  378  and the adjacent panel side edge. As discussed below, arch  394  flexibly supports the ventilation unit  274  above the head of the wearer. 
     When the rear nozzle assembly  280  is assembled, plate  352  is positioned against the open, forward directed surfaces of shell  320 . A knob  396 , also part of the rear nozzle assembly  282 , is mounted to the exposed back surface of the shell  320 . The knob  396 , seen best in  FIG. 40 , includes a cylindrical shaft  398 . Arcuately spaced apart teeth  402  extend radially outwardly along the shaft  398 . The knob shaft  398  is further formed to have a bore  399  that is open from the free end of the shaft. In one version of the invention, bore  399  extends through a sleeve  401  constrict with and located in shaft  398 . 
     The knob  396  also has a head  404  disposed over one end of the shaft  398 . Internal to the head  404  is ring  406  that extends around the portion of the shaft disposed in the head. Ring  406  is concentric with and spaced radially outwardly from shaft  398 . The ring  406  is formed with two diametrically opposed flexible tabs  408  (one shown). Each tab  408  has a single rib  410  that extends longitudinally along the outer surface of the tab. 
     The rear nozzle assembly  280  is constructed so that the knob shaft  398  seats in and extends through shell sleeve  340 . The free end of the shaft  398  seats against the annular space about the reinforcing rib  366  formed in plate  352 . A threaded fastener (not illustrated) extends through plate hole  364  and into bore  399  integral with knob  396 . This fastener holds the panel  352  to the shell  320 . When the rear nozzle assembly is so constructed, the ribs  410  integral with knob  396  seat in the void spaces between shell teeth  346 . 
     When head unit  270  is assembled, the head strap racks  312  seat in the slots between shell  320  and panel  352 . This is seen best in  FIG. 30 ; here it is understood the left-right sides of head unit being inverted. Specifically, the rack  312  integral with the right side head strap  302  seats in slot  359 . The rack  312  the forms part of the left side head strap seats in slot  392 . The rack teeth engage knob teeth  402 . 
     Rear nozzle tip  318 , now described by  FIG. 41 , includes a tubular base  412 . A lip  414  extends annularly around the open end of base  412  and away from the outer surface of base. Projecting upwardly from lip  414 , nozzle tip  318  has four equiangularly spaced apart mounting tabs  416 . Each tab  416  has a head  418  with a tapered outer surface. When the rear nozzle assembly  282  is put together, tabs  342  snap fit in shell opening  336 . Nozzle tip  318  is thus able to rotate relative to the axis that extends through opening  336 . 
     Nozzle tip  318  is formed with a head  420  that partially surrounds the bottom open end of base  412 . The nozzle tip  318  is formed so that tip head  420  is generally shell shaped such that the open end of base  338  opens into the void space defined by the concave surface of the head. 
     Returning to  FIG. 34  it can be seen that ventilation unit  274  includes lower and upper shells  428  and  430 , respectively, that house a fan  433  and a motor  434 . The lower shell  428 , best seen in  FIG. 42 , includes a base  432 . The lower shell  428  is formed so that the base  432  is widest at the center and relatively narrow at the opposed front and rear ends. Opposed side walls  434  extend upwardly from the side edges of base  432  extend along the longitudinal side edges of the base. Shell base  432  also has a cylindrical, hollow boss  436  that extends upwardly from the center of the base. Boss  436  is dimensioned to receive the fan motor  434 . Not identified is the opening in the center of the boss  436  wherein the rotating shaft of the motor extends therethrough. 
     The lower shell  428  is formed with two pairs of posts  438  and  440  that receive fasteners for holding the upper and lower shells together. Each of the posts  438  and  440  extends upwardly from the shell base  432 . A first pair of posts, posts  438 , are located adjacent the front end of the lower shell  428 . Each post  438  is located inwardly of an adjacent one of the side walls  434  at the front end of the shell  428 . Each post  440  is located inwardly of and adjacent one of the side walls at the rear of the shell  428 . 
     Two parallel ribs  442  and  444  extend inwardly from the shell base  432  and side wall  434  adjacent the rear opening these surfaces define. One rib, rib  442  extends inwardly around the open rear end of the shell. Rib  444  is located forward of and spaced apart from rib  442 . While not illustrated, it should be appreciated that similar ribs project outwardly from the base  432  and side walls  434  at the front end of the lower shell  428 . 
     The lower shell  428  also has a set of baffle plates  438  and  440  that partially surround and are radially spaced away from boss  436 . One plate, plate  438 , is generally S-shaped and starts at a locating slightly behind the open front end of the shell and the curves slightly inwardly. Baffle plate  438  then has a section that is has a radius of curvature that is centered on the axis of boss  436 . This particular section of the baffle plate  438  subtends approximately 150° of the circumference around the boss  436 . Baffle plate  438  also has a tail section that angles away from the S-section. This section of the baffle plate angles back to and abuts the adjacent shell side wall  434 . 
     Baffle plate  440  has an arcuate profile. The baffle plate  440  extends from the side wall  434  opposite the side wall with which plate  438  is associated. Baffle plate  440  is spaced forward of and substantially covers the open end of the lower shell  428 . The baffle plate  440  subtends an arc of approximately 70° around boss  436 . There is an arcuate separation of approximately 5 to 10° between the arcuate section of baffle plate  438  and the adjacent plate  440 . 
     The lower shell  428  is also formed so that there are a number of rectangular openings  442  in the base  432 . Openings  442  facilitate the securing of a motor cover  444  ( FIG. 34 ) to the exposed bottom surface of the lower shell  428  as discussed below. 
     The upper shell  430 , now described by reference to  FIG. 43 , includes a lid  450  from which two side walls  452  extends. Lid  450  has a shape that generally conforms to that of lower shell base  432 . The lid  450 , like the lower shell base  432  is curved along its longitudinal axis. Side walls  452  extend along the longitudinal side edges of the lid and curve downwardly from the lid. The lid  450  is formed with a circular center opening  453 . When the shells  428  and  430  are assembled together, opening  453  is coaxial with lower shell boss  436 . 
     The upper shell  430  is further formed to have ribs  454 ,  456 ,  458  and  460  similar to the ribs  442  and  44  of the lower shell  428 . Two parallel ribs  454  and  456  extend side wall to side wall at the front end of the upper shell. Rib  454  extends into the opening defined by the lid  450  and the adjacent side walls  452 . Rib  456  is parallel to and spaced behind rib  454 . Ribs  458  and  460  adjacent the rear opening of the upper shell  428  (ribs only partially shown.) The first rib, rib  458 , extends around the rear opening. The second rib, rib  460 , is spaced inwardly of rib  458 . 
     Fan  433 , illustrated in  FIGS. 44 and 44A , has a circular base  462 . A hollow boss  464  extends upwardly from the center of the base  462 . While the fan base is circular, it is not flat. Instead the base  462  curves upwardly to the hole formed by boss  464 . When the ventilation unit  274  is assembled, the fan  433  is fitted in the lower shell  428  for mounting to the motor  434  the fan boss  464  seats over shell boss  436 . The motor shaft mounts to the center of the fan boss  464  (motor shaft securement means not illustrated.) Located around the outer perimeter of base  462  are a number of arcuately spaced apart blades  466 . 
     A ring  468  is disposed over the top surfaces of the blades  466 . While in cross section ring  468  is flat, the ring has a tapered profile. Thus the inner edge of the ring is located above the outer edge. This change in lateral elevation of the ring  468  approximates the similar rise in elevation of the fan base  362 . This profile of having these surfaces rise to the center approximates the curvature towards the center of the caudal portion of the skull. This is the portion of the head over which the ventilation unit  274  is centered. 
     A grill unit  470 , also part of ventilation unit  274 , is disposed over the top of the upper shell  430 . As seen in  FIG. 45 , the grill unit  470  includes a frame  472 . The frame  472  generally has a shape similar to that of the lid. However, frame  472  is sized to fit wholly on the outer surface of the upper shell lid  472 . The frame, while formed from a set of flat strips of plastic, is shaped so that the strips are tapered inwardly. Thus the outer edges of the individual strips forming the frame are the surface of the grill unit  470  that seat against the adjacent outer surface of the upper shell lid  450 . 
     Formed integrally with frame  472  is a lattice  474 . The lattice is formed from a number of crossing webs. The lattice  474  extends over lid opening  453  and fan  433 . Shown extending downwardly from frame  472  are snap tabs  473 . When ventilation unit  274  is assembled snap tabs lock in openings  475  in the upper shell ( FIG. 43 ) to hold the grill unit to the upper shell. 
     The motor cover  444 , best seen in  FIG. 46 , is fitted to the exposed under surface of the lower shell base  432 . Motor cover  444  has a main body  480  that, while sheet like in shape, is curved along its longitudinal axis. Motor cover main body  480  is also curved into the center of the longitudinal center axis. Again, this curvature approximates the curvature of the portion of the skull over which the ventilation unit is typically seated. The front end of the main body has a straight edge; the rear end has a curved profile between the side edges. The motor cover  478  is further formed to have a lip  482  that extends upwardly from the outer perimeter of the main body  480 . More particularly, the lip  482  extends upwardly along the side and rear edges of the cover body  480 . 
     Four feet  484  interrupt the lip  482 . Each foot  484  is generally L-shaped and extends upwardly in the same direction as the lip  482 . Each foot  484  extends from the cover main body  480 . Two of the feet  484  are located immediately behind the front edge of the cover base  432 . The remaining two feet  484  are located forward of the curved rear end. Each foot  484  has an outwardly extending toe  486 . Toes  486  extend above the outer edges of the adjacent lip  482 . Motor cover  444  is secured to the lower shell  428  by snap fitting toes  486  in shell openings  442 . 
     Motor cover  444  is further formed so that, one each side, forward the rear end and rearward of the rear located feet  484 , there is a gap  489  in the lip  482 . 
     The motor cover main body  480  is formed with a slot  490  that extends along the longitudinal axis of the body. Slot  490  starts at the front end of the body. The slot  490  terminates at a location forward of the rear end of the main body  480 . Immediately rearward of the front end of the main body  480 , motor cover  444  is formed with two flexible fingers  492 . The fingers  492  are located diametrically opposite each other relative to slot  490 . The finger  492  are formed integrally with the rest of the motor cover  444 . Each finger  492  has a tip  494  that extends upwardly in the same direction as lip  482 . 
     Ventilation unit  274  is partially suspended above the head of the wearer by arch  388 . When head unit  270  is assembled, the upper end of the arch  388  is sandwiched between the outer surface of the lower shell  428  and the motor cover  444 . Fasteners, (not illustrated) hold the lower shell  428 , and therefore the whole of the ventilation unit  274 , to the arch. When motor cover  444  is secured to the lower shell  428  the arch extends through the gaps  489  in the cover lip  482 . 
     An accordion-like rear bellows  498 , seen in  FIGS. 33 and 34 , functions as the conduit from the rear end opening of the ventilation unit  270  to the rear nozzle assembly  282 . At the ventilation unit end, rear bellows  498  extends through the generally oval shaped opening formed by the ends of the lower and upper shells  428  and  430 , respectively. The forwardmost rib of the rear bellows  498  (rib not identified) is seated in the slot around this opening defined by adjacent lower shell ribs  442  and  444  the aligned adjacent upper shell ribs  458  and  460 . 
     The rear end of rear bellows  498  seats in the oval opening defined by the adjoining top ends of the rear nozzle assembly shell trunk  322  and plate collar  378 . The rear most rib of the rear bellows  498  is seated in the slot around this opening defined by shell ribs  330  and  332  and adjacent collar ribs  384  and  386 . 
     Front nozzle assembly  280  includes a pedestal  502  and a cap  504 . The pedestal  502 , seen best in  FIG. 47 , includes a hollow post  506 . Post  506  has a generally rectangular cross sectional profile. The base of the post  506  is secured to the section of the face frame support strap  294  immediately above the forehead band  288 . Not shown are the fasteners used to accomplish this securement. 
     Above post  506 , pedestal  502  has a head  508 . The head has a planar base  510  that extends outwardly from the front, back and sides of the pedestal. Side walls  512  that curve upwardly from the opposed longitudinal sides of the base  510  complete the head  508 . Two ribs  514  and  516  extend inwardly from the inner surfaces of the base  510  and side walls  512 . Rib  514  is located around the rear end of the pedestal head  508 . Rib  516  is parallel to and located forward of rib  514 . 
     Cap  504  seats over the pedestal head  508  to complete the front nozzle assembly  280 . Referring to  FIG. 48 , it can be seen that the cap  504  has a top panel  518  from which two side panels  520  curve downwardly (one side panel shown). The cap  504  is further formed so that the top panel  518  is curved along its longitudinal axis. When the front nozzle assembly  280  is put together, the cap side panels  520  abut the top edges of the pedestal head side walls  512 . 
     The front nozzle assembly cap  504  is further shaped so that a rib  519  extends along the longitudinal axis of the cap top panel  514 . The rib  519  is formed so as have slots  521  that extend inwardly from the sides (one slot shown.) At the front end of the top panel  518 , a tab  524  extends upwardly. Tab  524  is thus located immediately in front of rib  519 . A small web  525  extends perpendicularly from tab  524  to the rib  519 . Flange  525  is extends upwardly from the longitudinal axis of the rib  519 . Immediately behind tab  524 , an elongated slot  523  is formed in the rib  519 . 
     While not illustrated, it should be appreciated that a pairs of ribs extend inwardly from the inner surface of the cap top panel  518  and side panels  520 . A first one of these ribs abuts pedestal rib  514 . The second cap rib abuts pedestal rib  516 . 
     A front bellows  528  seen best in  FIGS. 31 and 34 , similar in structure to rear bellows  498 , serves as the conduit through which the forced air from the ventilation unit  274  is output to the front nozzle assembly  280 . The rear most rib internal to front bellows seats in the slot defined by lower shell ribs (not illustrated) and adjacent upper shell ribs  454  and  456 . The front most rib internal to the front bellows  528  seats in the slot defined by pedestal ribs  514  and  516  and the adjacent complementary ribs formed on the cap  504 . 
     Support strap  294  assists in the suspension of the ventilation unit  274  above the head of the wearer as now described by reference to  FIGS. 29 and 31 . Specifically, when the support strap  294  extends through the open front end of the motor cover  444  below the lower shell  428 . Returning to  FIG. 35 , it is noted that the support strap is formed with two rows of parallel openings  532 . Openings  532  extend laterally across the support strap  294 . The pairs of openings  532  are spaced apart from each other longitudinally along the length of the strap. 
     When support strap  294  is positioned between the lower shell  428  and the motor cover  444 , finger tips  494  seat in a pair of opposed strap openings  532 . This engagement of the motor cover  444  to the support strap  294  serves to provide a front support for the ventilation unit  274  above the head of the wearer. 
     Owing to the flexibility of the rear nozzle assembly arch  388 , ventilation unit  274  is able to pivot around the rear attachment of the unit rear nozzle assembly  282 . Motor cover fingers  492  are flexible. This means the position of the ventilation unit  274  can be selectively set to be relatively close to or spaced from the front nozzle assembly  280 . Collectively, this adjustability of the ventilation unit  274  means that the unit may be positioned relative to the head of the wearer wherein it will least likely impose a strain on the wearer. 
     Strain on the wearer is also reduced by the fact that the center of gravity of the ventilation unit  274  is relatively close to the seventh cervical vertebra. This goal is accomplished by shaping the components such as the lower shell  428 , upper shell  430  fan  433 , motor cover  444  and grill unit  470  so that they extend downwardly from their centers. As discussed above, this shaping approximates the back of the skull, the portion of the head against which the ventilation unit is typically fitted. 
     Still another reason this invention minimizes strain on the wearer is that the head unit is relatively light in weight. The head unit  270 , include the head band  272 , the ventilation unit  274  the front nozzle assembly  280 , the rear nozzle assembly  284  and face frame  286  typically has a weight of less than 450 grams. In more preferred versions of the invention, this assembly has a weight of less than 400 grams. 
     In regard to the minimization of this strain, experiments with head mounted equipment have shown that the strain is kept to the minimum if the center of mass is located over the seventh cervical vertebra. Thus a wearer of this head unit  270  is able to configure the unit so that the unit&#39;s center of mass is located as closely as possible positioned over this landmark. Again this position can be accomplished regardless of the head size of the wearer. 
     Regardless of the adjustment of the size of the head band  272  and the position/orientation of the ventilation unit  274  relative to the head band, the discharge opening of the front nozzle assembly  280  remains at a fixed position relative to the forehead band  288 . This means the transparent shield, which is suspended from the front nozzle assembly, remains a constant distance from the forehead band  288  and thus the face of the wearer. Therefore, the air flow discharged from the front nozzle assembly remains a constant distance away from the face of the wearer, regardless of the sizing of the head unit  270 . This means the front nozzle is positioned, regardless of head unit configuration, to ensure the discharge of air is at the appropriate position relative to the wearer&#39;s face to ensure, there is proper purging of CO 2  away from the face and delivery of relatively cool make up air. 
     Still another advantage with maintaining the front nozzle assembly  280  at a relatively constant position in front of the face is associated with hood/toga placement. As discussed below the hood/toga face shield  590  ( FIG. 52 ) is suspended from the front nozzle assembly  280 . Again since this assembly  280  is at relatively constant position relative to the face, transparent shield  590  is likewise at a constant distance from the face. This means the shield  590  can be located at a position so that regardless of head unit adjustment glare from either the light  276  or ambient light is keep to a minimum. 
     Similarly, regardless of the adjustment of the head unit, the rear nozzle assembly  282  remains essentially a constant distance from the neck of the wearer. This ensures that air discharged from tip  318 , regardless of head size and shape, optimally cool the neck. 
     Another advantage of so locating the transparent shield  590  essentially a constant distance from the face is that the shield can be sized to ensure that regardless of head size the field of view is essentially constant. In an ideal construction of the invention, no aspect of the head unit and the hood/toga is within the field of view except the transparent shield  590 . This can reduce feelings of claustrophobia an individual may developing using the system. 
     The support strap  294  is formed at the tail end thereof with a small downwardly directed tab  295  ( FIG. 50 ). This tab extends through slot  490  formed in the motor cover. The tab provides a visual indication of the extent to which the support strap  294  is extended into or retracted away from the ventilation unit  274 . 
     As seen in  FIG. 49 , the light  276  is a self-contained unit that includes an LED (not illustrated) or other light emitting element. Light  276  is pivotally mounted to a bracket  540  that is attached to forehead band  288 . Specifically, the bracket  540  includes a flat base  542 . Fasteners, (not illustrated) hold the bracket base  542  to the face frame forehead band  288  immediately below support strap  294 . Two arms  544  extend diagonally downward from base  542 . The light is pivotally mounted to and between the free ends of the bracket arms  544 . 
     A support wire  546  controls the up/down angle of the light  276 . The wire extends from a small tab  548  that is slidably mounted to the rib  519  on the top of the front nozzle assembly. The tab  548  has feet (not illustrated) that sit in rib slots  521 . The feet-in-slot arrangement facilitates the friction fitting of the tab  548  along the length of the rib  519  so that the tab can be slid to a left in position. 
     Wire  546  extends from tab  548  through cap opening  523  to the light unit  276 . The pivotal up/down position of the light  276  is set by adjusting the position of the tab  548  along the length of the front nozzle assembly  280 . 
     As seen in  FIG. 50 , a flex circuit  560  is mounted to the inner surface of the face frame chin bar  292 . Flex circuit  560  supports two lower power indicator LEDs  562  and  564  and a microphone  566 . While not illustrated it should be understood that layered on the flex circuit are the conductive traces that extend to the LEDs  562  and  564  and the microphone  566 . 
     More particularly, returning to  FIG. 35 , it can be seen that the face frame  286  around the posts  290  and chin bar  292  has an inwardly directed lip  568 . The flex circuit  560  has a main body  570  with generally rectangular shape. Three fingers  572  integral with the flex circuit main body  570  extend upwardly from the main body at longitudinally spaced apart locations along the upper side surface of the main body. The LEDs  562  and  564  are mounted to the outer surface of the two outer flex circuit fingers  572 . Each LED  562  and  564  extends through a separate opening  574  formed in the face frame chin bar lip  568 . 
     The microphone  566  is mounted to the center located flex circuit finger  572 . This finger  572  wraps around so as to overlap the flex circuit main body  570 . A cap (not illustrated) is fit over the chin bar  292  to cover the flex circuit. The microphone  566  extends through an opening in this cap so as to be directed to the mouth of the wearer. 
     A first one of the LEDs, arbitrarily LED  562 , performs the function of the power monitor enunciator  234  ( FIG. 22 ). Thus LED  564  is illuminated whenever the power monitoring circuit determines that the battery  562  is almost discharged. 
     The second LED, LED  564 , and microphone  566  are associated with the communications unit internal to the head unit  270 . The microphone  566  converts the words spoken by the wearer into electrical signals. The transceiver controller circuit  256  actuates switch  258  to place the communications system in the “mute” mode. 
     Also mounted to chin bar  292  are the wearer actuated switches  578 ,  580  and  582 , seen in  FIG. 51 , for controlling the system. The switches  578 ,  580  and  582  are formed from silicon rubber and have carbon contacts. A first one of the switches, switch  578 , is mounted in a first opening  584  defined by the chin bar  292 . The remaining two switches  580  and  582  are mounted in a second chin bar opening  586 . 
     Flex circuit main body  570  is disposed over the chin bar openings  584  and  586 . Formed on these surfaces of the flex circuit  560  are the conductive traces against which the switch carbon contacts abut (contacts not shown.) A first one of the switches, switch  578 , performs the function of switch  258 . This switch  578  is actuated to take the communications system in and out of the mute mode. The remaining two switches are analogues to switches  120  and  122 . Switches  580  and  582  thus are depressed to regulate the speed of the ventilation unit fan  278 . 
     An advantage of the above placement of switches  578 ,  580  and  582  is that the switches are immediately in front of the wearer. This makes it relatively easy for the wearer, by moving a hand towards his/her head to actuate the switches. Thus, an individual wearing this unit  270 , for most definitions of a sterile field, does not have to move his/her hand out of the field in order to actuate the switches. 
       FIG. 52  illustrates the transparent shield  590  attached to a hood or toga used with head unit  270 . Shown as a dashed line is the position internal to the perimeter of the shield  590  around which the sterile material forming the hood or toga is secured to the shield  590 . The top of the shield  590  is formed to have a tab  592 . Tab  592  has a slot shaped opening  594 . Opening  594  is rectangular in shape and on an axis parallel to the latitudinal, right-to-left axis of the shield  590 . The opening  594  further has an extension slot  595  that extends upwardly. Extension slot  595  is centered on the longitudinal, up-to-down axis of the shield  590 . 
     Shield  590  is formed to have two circular openings  596 . Each opening  596  is located adjacent a side edge of the shield  590  above the curved edge that functions as the transition edge between the side edge and the shield bottom edge. Cuts  598  extend radially from each opening  596 . It is appreciated that openings  594  and  596  are located in the perimeter section of the shield  590 . This is the section of the shield that is covered by the material forming the sterile hood or toga. 
     When the hood or toga is to be fitted to head unit  270 , the shield is placed over the head unit so that the tab  524  integral with the front nozzle assembly  280  is inserted in shield opening  590 . Front nozzle assembly web  525  seats in opening extension slot  595 . This seating of the shield  590  over the static tab  524  and web  525  serves to align the shield with the outer components of the head unit  270  and prevent rotation of the aligned shield. 
     Shield  590  is then curved around the face frame  286 . This flexing of the shield  590  brings each of the shield openings  594  into alignment with a separate one of the face frame pins  296 . Shield openings  594  are smaller in diameter than heads  298  of the mounting pins  296 . Thus, at this time the shield  590  is snap fitted over pins  296 . This engagement secures the shield  590  and the associated hood or toga, to the head unit. 
     In this version of the invention, there is spacing of at least 3 cm between the topmost attachment of the shield  590  to tab  524  and where the shield is attached to the two laterally spaced apart pins  296 . As a consequence of this arrangement, when the shield is fitted to the head unit  270 , the radius of curvature of the shield varies along the top to bottom longitudinal axis. More particularly at the top of the shield, adjacent the tab, there is a relatively wide diameter radius of curvature. Between pins  296  the shield has a smaller diameter of curvature, a more pronounced curvature. 
     An advantage of this construction is that near eye level the less curved, relatively flat, shield profile minimizes the amount glare. This arrangement also serves to assist in the shield&#39;s suspension of the material forming the hood/toga away from the forehead and top of the wearer&#39;s head. This feature provides a relatively large transparent shield-hood free space around the top of the head. This reduces the effort required to fit auxiliary equipment, such as a heads up display, a camera, other communication devices or lights around the wearer&#39;s head. 
     Another advantage of this configuration of this invention is that openings  594  and  596  serve as the means integral with the shield  590  for holding the shield to the head unit  270 . This arrangement eliminates the need to provide snap heads, magnets or hook-in-fabric fastening strips to the hood/toga on the shield in order to facilitate the attachment of the shield to the head unit. The elimination of these fastening members results in a like elimination of the costs associated with providing the shield with these components. 
     VII. Alternative Light, Communications and Fan Unit 
       FIG. 53  is a diagrammatic illustration of how a number of components of the personal protection system  10  of this invention are, in some versions of the invention, contained in a single housing  610 . Housing  610  is configured to be worn someplace on the individual. For example, the housing  610  may include a clip (not illustrated) so it can be attached to an article of clothing such as a belt. The housing  610  may alternatively include a strap (not illustrated) so it can strapped to the individual. 
     Internal to the housing  610  is the power supply  70 . Also integral with the housing is the transceiver  242 . A cable  612  that leads to head of the individual includes the conductors that are connected to the microphone  238  and speaker  240 . In these and other versions of the invention, the microphone and speaker may be built into a head set separate from the structure used to suspend the hood. Also disposed inside housing  610  is a fan  52   a . The majority of the airflow output by the fan is discharged through a flexible tube  614 . Tube  614  is connected to the output vents in the body support structure from which the air should be discharged. 
     A light generating unit  616  is also contained housing  610 . The light generating  616  unit may contain an LED or an incandescent bulb such as a halogen bulb. A fiber optic cable  618  extends from the light generating unit  616 . The distal end of the fiber optic cable is attached to the light emitting head  620  attached to the body support structure. 
     In this version of the invention, the outlet flow from the fan  52   a  is discharged from two ports, (not shown). The proximal end of tube  614  is connected to one of the ports. The second port leads to a duct  622  in the housing. Duct  622  is located between the face of the sub housing  302  in which the light generating unit  616  that would be closest to the wearer of the system  10  and the adjacent structural wall of the housing  610 . Thus, the system is actuated fan  52   a  continually blows new make-up air into duct  298 . The air is discharged from exhaust ports  624  formed in the side of the housing  610 . This constant supply of this air minimizes the extent to which the heat generated by the light generating unit  616  convectively warms the housing  610  and the adjacent portion of the body of the wearer. 
     An advantage of this version of the invention is that the majority of the weight of the active components of the personal protection system  10  are suspended from the waist or other body part of the user where the presence of such weight does not induce significant appreciable physical stress. 
     VIII. Alternative Features 
     Body-worn support structures for suspending the hood other than the illustrated and described helmet may be employed in this invention. One possible structure is a shoulder mounted frame. This frame contains structural members for supporting the hood. This fan or light generating unit may be directly mounted to this support structure. In versions of the invention where both components are so mounted to the support structure, a duct is present to circulate a fraction of the air discharged by the fan around the light generating unit. Alternative embodiments of this version of the support structure of this invention may simply have ducts for receiving the air and ports through which the air is discharged and a light emitting head for emitting the light. In these versions of the invention the waist mounted unit contains the fan and the light generating unit. 
     In some versions of the invention, the body support structure includes a vest like garment worn about the trunk of the wearer. Integral with this garment are one more supports from which the hood is suspended. 
     Also, in some versions of the invention, the support unit may include an outwardly directed speaker. For example, this speaker could be mounted to flex circuit  560 . In these versions of the invention, there is also an amplifier capable of amplifying the signals produced by microphone  566 . These signals are broadcast by this speaker through the hood/toga into the surrounding environment. This arrangement eliminates the need to provide RF signal transceivers. 
     It may also be desirable to provide the transparent shield of the hood/toga with at least one section that transmits sound. (Generally the material forming the transparent shield absorbs or reflects sound.) Thus, the transparent shield could be formed an opening that is generally aligned with the mouth of the wearer. This opening is covered with a section of the sterile material from which the rest of the hood/toga is formed. This construction can eliminate the need to provide any assembly for broadcasting or amplifying the speech of the wearer. 
     Alternatively the transparent shield opening may be covered with material that absorbs and retransmits sound waves. Electrometric materials such as a silicon rubber may perform this function. 
     It should likewise be appreciated other duct assemblies may be provided to direct air from the ventilation fan to the light generating unit. For example, there may be a duct within either the front or rear nozzle assembly that leads directly to the light source. This duct extends to a conduit, which may be flexible, that extends to the light source. In some versions of the invention, this conduit opens into the inside of the housing of the light source. Thus, the air passes directly over the heat generating, light emitting elements or heat sink elements internal to the light source housing. 
     Alternatively, in some versions of this invention, the light source has its own ventilation fan. This arrangement may be useful if it is necessary to flow large volumes of air over the light source. 
     In either of the above versions of the invention, the light source may be formed with a conduit through which the air introduced into the source is exhausted. This conduit has an exhaust port that opens away from the wearer. 
     It may also be desirable to position a temperature sensitive transducer adjacent the heat generating components of the light source. The signal output by this sensor can be used to regulate the light source and/or the fan that provides the air for cooling the light. Thus when this sensor indicates the temperature adjacent the light source is rising to uncomfortable levels, the current regulator  230  could respond by reducing the power supplied to the light. When this condition is detected, alternatively, microcontroller  118  could step up the speed of the fan so as to increase the air flow over the light source. 
     It should be appreciated that there are reasons other than wearer comfort for so controlling the temperature of the light source and the space surrounding the source. This excessive heating of the light source can appreciably diminish its useful life. In some instances, the excessive heating of the source can cause its failure. Also, this heat, if not exhausted, could potentially warm the user to the point at which the skin blisters or is burned. 
     In some versions of the invention a heat pipe formed from thermally conductive material extends from the light source. This heat pipe may extend to a duct that extends from the fan. 
     An anti-glare hood may be fitted over the light emitting head so as to extend between the head and the inner surface of the transparent shield. The inner surface of this hood is formed from light reflective or absorbing material. This arrangement reduces, if not eliminates, the amount of light emitted by the head that is reflected by the inner surface of the transparent shield back to the wearer as glare. 
     This hood may be formed from rigid or flexible material. One advantage of employing flexible material is that it can ensure the hood abuts the inner surface of the transparent shield when the shield is fitted to the helmet or head unit. 
     Some light systems may also be configured to provide the wearer with short bursts of high intensity light. This light is provided in response to depression of a specific control switch. The light burst may be provided in situations in which a very large amount of light is required. Only a burst of light for a period between 1 to 10 minutes is provided. Only the burst is provided so as to minimize the possibility this high driving of the light source results in excessive heat being output or the source or the source being excessively operated to the level at which it may burn out. 
     Devices other than the bellows may be employed as the adjustable conduits that connect the ventilation unit  274  to the front and rear nozzle assemblies  280  and  284 , respectively. For example, telescoping tubes and/or tubes with flexile joints may be employed as these conduits. 
     Further, there is no requirement that in all versions of the invention two spaced apart support members, support strap  294  and arch  394  both be provided to suspend the ventilation unit  274  above the head band  272 . In some versions of the invention, a single support member or support post may be all that is required. 
     Also, in not all versions of the invention may it be necessary to attach the front ventilation unit  280  to the head band  272 . Thus, in some versions of the invention the adjustable conduit that extends from the ventilation unit  274  to the front nozzle assembly  280  provides support for suspending the front nozzle assembly in a specific position relative to the head band. 
     Further, there is no requirement that the all versions of the invention include both the front and rear nozzle assemblies  280  and  282 . Clearly most units will include the front nozzle assembly. 
     Thus it should be clear that the foregoing description is directed to specific embodiments of the invention. Therefore, it is an object of the appended claims to cover all such modifications and variations that come within the true spirit and scope of this invention.