Abstract:
A single layer sound insulated door assembly, and automatically releasing latch to open the door assembly in response to predetermined indicators of fire in the structure and a labyrinthine seal mechanism which limits sound transmission through the door assembly. An acoustical smoke vent is sound insulated and the doors are sealed to the curb by means of a unique labyrinthine gasket assembly effective at limiting sound transmission through the vent. The acoustical smoke vent of the present invention achieves a sound transmission class of STC 45 or better without the need for double layer door assemblies.

Description:
CLAIM TO PRIORITY  
       [0001]    This application claims priority to U.S. Provisional Patent Application Serial No. 60/439,044 entitled “Acoustical Smoke Vent,” filed on Jan. 8, 2003. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The invention relates to roof mounted smoke vents for venting heat, pressure and smoke from a structure during a fire. More particularly, the invention relates to a sound insulated smoke vent with improved acoustical properties for inhibiting sound transmission through the vent when it is in a closed position.  
         BACKGROUND OF THE INVENTION  
         [0003]    It has been common practice for a long period of time for firefighters to create openings in the upper portions of burning structures in order to vent smoke, heat and pressure. Virtually everyone has seen the image of firefighters breaking upper story windows in buildings to allow the release of the products of combustion. Particularly when dealing with very tall structures, it can be at least inconvenient and often dangerous for firefighters to gain access to the upper parts of a building in order to create ventilation.  
           [0004]    Thus, it has been common for decades in larger structures to provide automatically opening smoke vents on the roof or upper stories of large structures. Roof mounted smoke vents are essentially a door or opening on the roof of a structure. These vents are configured to open automatically upon the occurrence of increased temperature pressure or presence of smoke within the building. In its most basic form, a smoke vent is a spring-loaded door, with the spring-load biased toward an open position. The door is held closed by a fusible link. When the fusible link melts due to excessive heat, the door is released and the spring bias opens the door automatically. More sophisticated release mechanisms have been developed over the years, but this is the basic principle of an automatic smoke vent has remained the same.  
           [0005]    As discussed above, smoke vents are generally equipped with an automated instantaneous opening mechanism. The opening mechanism may be controlled by a fusible link, a remote electrical control or a pneumatic control. These controls are activated by melting of the fusible link, or sensing of an abnormal condition by a temperature sensor, a pressure sensor, a smoke detector or some other similar sensor.  
           [0006]    Conventional smoke vents typically have a door or doors that open directly from the interior of a structure to the ambient atmosphere. A common problem with such smoke vents is that the vent, even when closed, provides an inlet for ambient noise from outside the building. In the case of a structure that includes a theatre or auditorium, this outside noise can create significant distraction and disruption for occupants of the building. This is particularly true if the structure is located near a busy street, a construction site, an airport or another source of chronic noise.  
           [0007]    In addition, the design of some conventional smoke vents causes vibration or interaction, either between the components of the smoke vent itself or between the vent and the surrounding roof where the smoke vent is mounted. Vibration of this kind is highly disruptive and unwelcome, and is often more disturbing than the noise that triggers it, especially during a concert or performance in an auditorium or theatre.  
           [0008]    When sound waves come into contact with a barrier, some of the energy from the vibrating air molecules transfers to the barrier. This causes the barrier itself to vibrate, which then causes air on the other side of the barrier to be set into motion creating sound waves. The transmission of sound waves through barriers can be reduced in a number of ways. The greater the mass of the barrier, the less sound energy is transmitted through the barrier. In addition, sound transmission can be reduced by the use of sound damping materials. Damping materials are typically limp masses that dampen the sound energy passing through them. Further, sound absorbing materials absorb and trap sound energy. Sound absorbing materials include insulation batts and the like. Finally, the stiffness of the barriers also is a factor in sound transmission. A barrier such as steel may be stiffened to reduce sound transmission.  
           [0009]    The sound transmission of a barrier is commonly rated in terms of Sound Transmission Class, also referred to as Sound Transmission Coefficient (STC). STC is a single-figure rating derived in a prescribed manner from sound transmission loss values. The rating provides an estimate of the performance of a component in common sound insulating situations.  
           [0010]    The higher the STC value, the better the sound deadening performance. For example, an STC 45 barrier will reduce the level of sound heard on the quieter side of the barrier by approximately forty-five decibels from that heard on the noisy sound of the barrier. STC values are used to define the sound deadening qualities of a barrier between a sound source area and a sound receiving area.  
           [0011]    A two room test is generally used to determine the sound insulation effectiveness of a construction component. In this test, the component is mounted on a heavily insulated wall. A steady sound is generated on one side of the wall and the sound that passes through the component is measured on the other side. The measurement of sound levels is then recorded at several different frequencies over a range of 125 to 4000 Hz. The difference in sound levels (in dB) between the two sides of the component determines the transmission loss level. For instance, if an 80 dB signal is reduced to 10 dB on the other side of the wall, the transmission loss is 70 dB.  
           [0012]    As an example, an STC value of 50-60 is considered excellent for most structural needs. A barrier having an STC value of 50-60 will prevent most loud sounds from being heard on the other side. An STC value of 40-50 is considered to be very good. On the quiet side of an STC 50 barrier, loud speech will be heard only. faintly. At an STC level of 20-25, sound insulation is considered to be very poor, with even quiet speech being audible on the other side of a barrier.  
           [0013]    Sound insulated smoke vents have been developed in an effort to resolve the problem of noise leakage. Commonly, sound insulated smoke vents utilize double layer door designs to minimize acoustic transmission. These acoustical smoke vents will have a door or doors opening above roof level outside a structure and another set of doors that open at ceiling level inside the structure with a sound insulating space between the doors. Typically the upper set of doors opens outwards at the roof level and the lower set of doors opens into the building space at the ceiling level though other configurations are possible.  
           [0014]    Double layer door designs require more complex opening mechanisms than single layer door designs, and the greater complexity make them more likely to require field adjustment and more prone to jamming and failure. They also require greater maintenance because of the more complex mechanisms.  
           [0015]    When maintenance or testing of such double layer doorarrangements is necessary, a maintenance person must often reach down through the open upper level doors to grasp the inner doors to pull them closed to reset them. This can create a significant risk that the maintenance person may fall through the door opening into the building. Theatres and auditoriums where sound insulated smoke vents are typically used, often also have very high ceilings. The combination of these factors can create a risk of serious injury if a maintenance person falls through the door opening.  
           [0016]    Thus, there is a need for an acoustical smoke vent that effectively muffles external noise and increases safety while being simple in operation and construction. In addition, there is a need for an acoustical smoke vent that eliminates the need to have double layer door systems in the smoke vent. Such a smoke vent would be simpler, safer and more reliable than those currently available.  
         SUMMARY OF THE INVENTION  
         [0017]    The present invention solves most of the above-discussed problems by providing an effective acoustical smoke vent including a single layer door assembly. The acoustical smoke vent of the present invention is sound insulated and the doors are sealed to the curb by a unique labyrinthine gasket assembly effective at limiting sound transmission through the vent. The use of a single layer door system increases safety and reliability and allows for the use of a simple latching and release system.  
           [0018]    The acoustical smoke vent disclosed herein is simpler and safer to reset and close than conventional double layer door smoke vents.  
           [0019]    The acoustical smoke vent of the present invention generally includes a sound insulated curb assembly which is attached to the roof, a single layer sound insulated door assembly, an automatically releasing mechanism to open the door assembly in response to predetermined indicators of fire in the structure, and a labyrinthine seal mechanism which limits sound transmission through the door assembly. The acoustical smoke vent utilizes acoustical materials as well as structural geometry in which the material is located to minimize sound transmission.  
           [0020]    The acoustical smoke vent may also be attached to a wall near the top of a structure. The acoustical smoke vent of the present invention achieves a sound transmission class of STC 45 or better without the need for a double layer door assembly.  
           [0021]    The labyrinthine gasket generally includes a door portion and a curb portion. The door portion of the labyrinthine gasket runs around and is attached to the inside perimeter of the doors. The curb portion of the gasket surrounds the edge of the curb opening. The door gasket may include double rows of elastomeric gasket material. The hinge side door gasket desirably includes an inner gasket and an outer gasket. The door portion of the labyrinthine gasket is secured to the doors by gasket retainer extrusions.  
           [0022]    In cross-section, the gaskets include an extrusion portion and a sealing portion and define a lumen. The sealing portion desirably defines a series of peaks and troughs to facilitate sealing with the edge surface of the curb.  
           [0023]    The labyrinthine gasket also has a curb portion. The curb portion is desirably secured to the perimeter of the curb opening by gasket retainer extrusions in a fashion similar to the door portion.  
           [0024]    The gasket on the latch side and end sides of the door is unique in construction as compared to the other parts of the labyrinthine gasket. Latch side gasket includes an inner portion and outer portion. The outer portion is secured to the doors via gasket retainer extrusions. The inner portion is integrally formed, as a unit, along with the outer portion but is not otherwise directly secured to the doors. The inner portion includes a door sealing portion and gutter sealing portion. The gutter separates the two doors in a two door embodiment of the invention.  
           [0025]    The door sealing portion and gutter sealing portion include peaks and troughs and define a lumen similar to other parts of the labyrinthine gasket. The outer portion of latch side gasket further includes a cylindrical extension. The cylindrical extension is adapted to overhang into the gutter and over the sides of the curb assembly and to seal thereto. The cylindrical extension may be protected by an overhang of the latch side of the door. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]    [0026]FIG. 1 is a perspective view of a partially assembled acoustical smoke vent in accordance with the present invention;  
         [0027]    [0027]FIG. 2 is a side elevational view of a curb assembly in accordance with the present invention;  
         [0028]    [0028]FIG. 3 is a side sectional view of an acoustical smoke vent in accordance with the present invention;  
         [0029]    [0029]FIG. 4 is a perspective view of a curb assembly in accordance with the present invention;  
         [0030]    [0030]FIG. 5 is a partially exploded view of a curb assembly;  
         [0031]    [0031]FIG. 6 is a perspective partially exploded view of the curb assembly in accordance with the present invention indicating the location of a portion of a labyrinthine gasket;  
         [0032]    [0032]FIG. 7 is an exploded perspective view of a gutter assembly;  
         [0033]    [0033]FIG. 8 is cross-sectional view of the gutter assembly;  
         [0034]    [0034]FIG. 9 is an exploded perspective view of a door;  
         [0035]    [0035]FIG. 10 is a partially exploded perspective view of a door assembly;  
         [0036]    [0036]FIG. 11 is a partially exploded perspective view of the door assembly;  
         [0037]    [0037]FIG. 12 is a partial perspective view of the curb assembly and operating mechanism;  
         [0038]    [0038]FIG. 13 is a detailed sectional view of a latch portion of a labyrinthine gasket; and  
         [0039]    [0039]FIG. 14 is a detailed sectional view of a hinge portion of the labyrinthine gasket. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]    Acoustical smoke vent  20  generally includes curb assembly  22 , door assembly  24 , labyrinthine gasket  26  and actuator assembly  28 . Acoustical smoke vent  20  is intended for attachment to the upper portion of a structure. Typically acoustical smoke vent  20  will be secured to the roof of a structure via curb assembly  22 . Acoustical smoke vent  20  may also be adapted to be secured to a wall or other part of the upper portion of a structure in order to vent smoke, heat and pressure in the event of a fire or explosion.  
         [0041]    Referring particularly to FIGS. 1, 2,  3  and  5 , curb assembly  22  generally includes internal frame  30 , exterior flashing  32  and sound insulation  34 . As best seen in FIG. 5, frame  30  is a generally rectangular topless and bottomless box including long sides  36  and short sides  38 . Long sides  36  and short sides  38  are interconnected and connected to attachment flange  40 . Frame  30  may further include angle braces  42 . Frame  30  may be assembled from any strong rigid material, but desirably is formed from welded steel or aluminum sheet metal. Frame  30  supports other structures that make up acoustical smoke vent  20 .  
         [0042]    Flashing  32  generally covers and surrounds frame  30 , leaving an air space in between. Flashing  32  generally includes long sides  44  and short sides  46  joined at comers  48 . Preferably, long sides  44  and short sides  36  are joined by welding or other highly weather resistant methods. Flashing  32  further includes flange  50  and is made from a weather resistant material such as aluminum or galvanized steel. Desirably frame  30  and flashing  32  are formed of sheet metal of unequal thickness.  
         [0043]    Referring to FIG. 5, sound insulation  34  for curb assembly  22  typically includes composite acoustic barrier  52  and insulation  54 . Composite acoustic barrier  52  is, for example, a composite of loaded vinyl attached to an open cell foam decoupling layer. Insulation  54  is typically R-13 fiberglass or mineral wool.  
         [0044]    Referring to FIGS. 7 and 8, curb assembly  22  may further include counter flash gutter  56 . Counter flash gutter  56  includes gutter  58 , trough  60 , acoustic barrier  62  and insulation  64 . Composite acoustic barrier  62  lines the interior of trough  60  and is further separated from gutter  58  by insulation  64 . Desirably, counter flash gutter  56  is assembled with rust resistant screws  66 . Composite acoustic barrier  62  and insulation  64  are similar to that used in the remainder of acoustical smoke vent  20 . Note that gutter  58  and trough  60  are desirable formed of sheet metal of unequal thickness. An internal layer of a first thickness and an external layer of a second thicknesses tend to cancel out resonant frequencies between the layers and to reduce sound transmission.  
         [0045]    Referring to FIGS. 3, 9,  10  and  11 , door assembly  24  generally includes one or two doors  68 . A larger number of doors  68  may be included. However, two is the most commonly utilized number. Doors  68  are operably connected to curb assembly  22  by hinges  70 .  
         [0046]    Referring to FIGS. 3, 9 and  10  doors  68  generally include cover  72  and sound deadening  74 . Cover  72  generally includes door pan  76 , liner  78  and support angle  80 . Door pan  76  and liner  78  serve to completely enclose doors  68  structure. Support angle  80  desirably runs lengthwise through doors  68  and is secured to liner  78  desirably by welding. Referring particularly to FIGS. 9 and 10, door pan  76  and liner  78  surround composite acoustic barrier  82  and insulation  84 .  
         [0047]    Door pan  76  is formed from sheet metal of a different thickness from liner  78 . For example, door pan  76  may be formed from fourteen gauge (0.079 inch) sheet steel and liner may be formed from twelve gauge (0.108 inch) sheet steel. The difference in thickness of the layers tends to create unequal resonant frequencies between the two structures and to minimize sound transmission. In addition, door pan  76  desirably is isolated from liner  78  as much as possible to minimize sound transmission. Still further, the thickness of the air cavity enclosed by door pan  76  and liner  78  should be maximized as much as practical to reduce sound transmission. For example, a three-inch air space between door pan  76  and liner  78  is desirable. These principles apply to the construction of curb assembly  22  as well.  
         [0048]    Referring to FIGS. 6, 11 and  13  labyrinthine gasket  26  generally includes door portion  86  and curb portion  88 . Labyrinthine gasket  26  is formed of a resilient elastomeric material. For example, a suitable elastomeric material is a soft grade closed cell EPDM (ethelyne propylene diene monomer) material. Referring particularly to FIG. 11, door portion  86  of labyrinthine gasket  26  runs around perimeter  90  of doors  68 . Door portion  86  includes hinge side gasket  92 , latch side gasket  94  and end gasket  96 . Hinge side gasket  92  desirably includes an inner gasket  98  and an outer gasket  100 . Hinge side gasket  92 , latch side gasket  94  and end gaskets  96  are all desirably secured to doors  68  by gasket retainer extrusions  102 .  
         [0049]    Gasket retainer extrusions  102  are a generally U shaped channel secured to perimeter  90 . Gasket retainer extrusions  102  grip labyrinthine gasket  26  and secure it in place. Gasket retainer extrusions  102  may be riveted through liner  78  to fasten them to doors  68 .  
         [0050]    Hinge side gasket  92 , latch side gasket  94  and end gaskets  96  meet at comers  104 . At comers  104  latch side gasket  94  is joined to end gaskets  96  desirably at a 45° mitered joint secured using an adhesive such as Lock-tite 401®. Hinge side gasket  92  is joined to end side gaskets  96  at the hinge side comers in a ninety degree butt joint also joined with an adhesive such as Lock-tite 401®. Desirably, hinge side gasket  92 , is of a hollow cross-sectional construction. As best seen in FIG. 3, cross-section  106  includes extrusion portion  108 , sealing portion  110  and encloses lumen  112 . Sealing portion  110  desirably defines a series of peaks  114  and troughs  116 . Extrusion portion  108  is shaped to fit into gasket retainer extrusion  102 . Desirably, hinge side gasket  92  is formed of grade zero closed cell EPDM foam. Latch side gasket  94  and end gaskets  96  preferably are grade zero closed cell EPDM foam.  
         [0051]    Referring particularly to FIGS. 6 and 14, curb portion  88  of labyrinthine gasket  26  includes curb hinge side gasket  118 , curb end gaskets  120  and gutter gasket  122 . Curb hinge side gasket  118 , curb end gasket  120  and gutter gasket  122  are desirably secured to opening perimeter  124  by gasket retainer extrusions  102  in a fashion similar to door portion  86 . Curb hinge side gasket  118  meets curb end gaskets  120  at opening comers  126 . At this joint, curb hinge side gasket  118  is desirably joined to curb end gaskets  120  at a forty five degree miter joint glued together with an adhesive such as Lock-tite 401®. Curb portion  88  of labyrinthine gasket  26  is preferably formed from grade zero closed cell EPDM foam.  
         [0052]    Latch side gasket  94  and end gaskets  96  on door  68  are different in construction as compared to hinge side gasket  92 , curb hinge side gasket  118 , curb end gasket  120  and gutter gasket  122 . Latch side gasket  94  and end gaskets  96  includes inner portion  128  and outer portion  130 . Outer portion  130  is secured to doors  68  via gasket retainer extrusions  120 . Inner portion  128  is integrally formed along with outer portion  130  but is not otherwise directly secured to doors  68 . Inner portion  128  includes door sealing portion  132  and gutter sealing portion  134 . Door sealing portion  132  and gutter sealing portion  134  desirably include peaks  114  and troughs  116  and define lumen  112  similar to hinge side gasket  92 , end gaskets  96 , curb hinge side gaskets  118  and curb end gasket  120 . However, inner portion  128  defines door sealing portion  132  and gutter sealing portion  134  on opposed sides of lumen  112 . Outer portion  130  of latch side gasket  94  further includes cylindrical extension  136 . Cylindrical extension  136  is adapted to overhang into gutter  58  and around opening perimeter  124  of curb assembly  24  to seal thereto. Desirably cylindrical extension  136  is protected by overhang  138  of door  68 .  
         [0053]    Referring particularly to FIGS. 1, 3,  11  and  12 , actuator  28  generally includes release mechanism  140 , opening mechanism  142  and closing mechanism  144 . Actuator  28  is connected to sensors (not shown) which sense predetermined indicia of a fire within a structure. Indicia may include smoke, heat or pressure. Such sensors are well known in the art and need not be discussed further here. Release mechanism  140  may commonly include a motor and winch located within acoustical smoke vent  20 , a remotely located connected to the acoustical smoke vent  20  by cables or a fusible link based latch mechanism, sometimes known as a pyrolatch.  
         [0054]    In one embodiment, release mechanism  140  includes hook  146 , catch  148  and opening controller  150 . As best seen in FIG. 3, hook  146  engages catch  148  to hold doors  68  in a closed position. Opening controller  150  controls the operation of catch  148  to automatically open doors  68  in response to predetermined criteria indicating fire within a structure. Opening controller may take the form of a fusible link  151 . When exposed to a predetermined elevated temperature fusible link  151  melts and releases hook  146  from catch  148 . Other methods of accomplishing this function will be apparent to those skilled in the art. Mechanisms like opening controller  150  are well known in the art and will not be further described here.  
         [0055]    In another embodiment, release mechanism  140  may further include manual release  152 . Manual release  152  includes pull handle  154 , cable  156  and controller lug  158 . Pull handle  154  is located for convenient access on the exterior of acoustical smoke vent  20 . Cable  156  interconnects pull handle  154  with controller lug  158 . If it is necessary to manually open acoustical smoke vent  20 , a user, such as a firefighter, can grasp and pull pull handle  154 , tensioning cable  156 , which in turn moves controller lug  158  which releases doors  68  to open acoustical smoke vent  20  overriding automatic systems.  
         [0056]    Opening mechanism  142  generally includes biasing member  160 , damping member  162  and hold open  164 . Biasing member  160  serves to bias doors  68  toward an open orientation. Biasing member  160  may include springs, weights or systems utilizing compressed gas as well as any other means of biasing doors  68  toward an open position. Desirably, as best seen in FIGS. 1 and 3, biasing member  160  is a gas spring assembly  166 . Gas spring assembly  166  includes door bracket  168 , curb bracket  170  and gas strut  172 . Gas strut  172  interconnects door bracket  168  and curb bracket  170  and provides a biasing force to open doors  68 . This arrangement is exemplary and other structures for biasing member  160  will be apparent to individuals skilled in the art.  
         [0057]    Damping member  162  generally includes door bracket  174 , shock absorber  176  and attachment  178 . Shock absorber  176  interconnects door bracket  174  and attachment  178 . Attachment  178  is supported by angle brace  42 . Shock absorber  176  is desirably a hydraulic shock absorber or shock absorbers as needed to counteract the biasing force applied by gas spring assembly  166  and allowed doors  68  to open slowly. Damping member  162  counters the tendency of biasing mechanism to slam doors  68  open abruptly. This arrangement is exemplary and other structures for damping member  162  will be apparent to individuals skilled in the art.  
         [0058]    Hold open  164  includes hold open arm  180  and guide track  182 . Hold open arm  180  is hingedly attached to doors  68  and slidingly attached to guide track  182 . Hold open  164  serves to support door in an open position once it is fully open to prevent unintended closure thereof. Hold open  164  latches in the open position and can be manually released. This arrangement is exemplary and other structures for hold open  164  will be apparent to individuals skilled in the art.  
         [0059]    In another embodiment, opening mechanism  164  and closing mechanism  144  may be combined as best seen in FIG. 12 generally including motor assembly  184 , cable  186  and sheaves  188 .  
         [0060]    Motor assembly  184  includes motor box  190 , shaft  192  and winch drums  194 . Motor box houses motor  196  and supports shaft  192 . Shaft  192  supports winch drums  194 . Winch drums  194  desirably are keyed to shaft  192 . In this embodiment opening controller  150  controls motor  196 .  
         [0061]    Cables  186  are disposed around winch drums  194  and may be wound onto and paid out from winch drums  194  by motor  196  as commanded by opening controller  150 .  
         [0062]    Cables  186  are fed over sheaves  188 . Sheaves  188  are located in multiple pulleys  198  as necessary to interconnect cable  186  between winch drums  194  and doors  68  in order to pull doors  68  to a closed position when motor  196  is actuated to turn shaft  192  and winch drums  194 . One exemplary configuration for motor  196 , winch drums  194 , cables  186  and sheaves  186  is shown in FIG. 12. One skilled in the art can make multiple other arrangements of cables and pulleys in order to accomplish the same task.  
         [0063]    Additionally, closing mechanism  144  may be omitted from acoustical smoke vent  20  and acoustical smoke vent  20  may be manually reclosed as needed.  
         [0064]    In operation, acoustical smoke vent  20  is secured to a structure by attachment flange  40 . An opening is made in the roof of the structure appropriately sized to accommodate acoustical smoke vent  20  and attachment flange  40  is secured around the perimeter of the opening. Attachment flange  40  may be secured to the structure by bolts, rivets, nails or other appropriate fasteners depending upon the construction of the structure.  
         [0065]    In the event of a structural fire, actuator  28  is connected to sensors (not shown) which sense predetermined indicia of a fire within a structure. Indicia may include smoke, heat or pressure. Actuator  28  then commands opening mechanism  142  to open doors  68 . In one embodiment, opening mechanism  142  moves catch  148  to release hook  146 . At which point biasing member  160  which has been applying a biasing force to doors  68  is free to move to open doors  68 . Damping member  162 , in the form of shock absorbers  176 , resists and the force applied by biasing member  160  and slows the motion of doors  68  in order that doors not spring or slam open which could cause potential harm to an individual in the area of acoustical smoke vent  20  or damage acoustical smoke vent  20 . In another embodiment, motor  184  is actuated to pay out cables  186  from winch drums  194  to allow biasing member  160  to open doors  68 .  
         [0066]    In the event that it is necessary to manually open acoustical smoke vent  20 , an operator, such as a firefighter, may grasp pull handle  154  to activate manual release  152 . Upon pulling handle  154 , cable  156 &#39;s tension causes motion in controller lug  158  which mechanically releases catch  148  to open doors  68 .  
         [0067]    In the event that maintenance is necessary for acoustical smoke vent  20 , doors  68  may be opened either remotely or by operation of manual release  152 . Once doors  68  are opened, hold open  164  prevents door  68  from closing should it be necessary for maintenance personal to disconnect gas struts  172  and/or shock absorbers  176 .  
         [0068]    When it is necessary to close acoustical smoke vent  20 , a maintenance person may manually release hold open arm  180  from guide track  182  and manually closed door  68 . Alternately, in some embodiments, doors  68  may be closed remotely by actuating motor assembly  184 . When motor assembly  184  is actuated, shaft  192  is turned by motor  196  causing winch drums  194  to take up cables  186 . Cables  186  pass over a series of sheaves  188  to pull doors  68  closed. In embodiments equipped with a fusible link based latch  151 , upon closing, catch  148  engages hook  146  securing doors in a closed position.  
         [0069]    Sound insulation of acoustical smoke vent  20  is achieved by a combination of sound insulation enclosed within doors  68 , curb assembly  22 , the structure of the acoustical smoke vent  20  and the qualities of labyrinthine gasket  26  as described above. Labyrinthine gasket  26  provides a multilayered acoustic seal between door assembly  24  and curb assembly  22 , thus sealing out unwanted acoustic energy that might leak in through gaps between doors  68  and curb assembly  22 . In addition, the thickness of the sheet metal and structure of door assembly  24  and curb assembly  22  in combination with the above discussed factors combine to achieve an STC of forty five or better.  
         [0070]    Further, door assembly  24  is interconnected with curb assembly  22  via hinges  70 . Hinges  70  are acoustically isolated from curb assembly  22  by composite acoustic barrier  52  and insulation  54 . This contributes further to the sound deadening qualities of the acoustical smoke vent  20 . Thus, acoustical smoke vent  20  can achieve a sound transmission class of  45  or better without the need for having a double layer door assembly.  
         [0071]    The present invention may be embodied in other specific forms without departing from the spirit of the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.