This invention relates to a novel air curtain device suitable for
use in detecting certain characteristic vapors emitted from objects,
particularly individuals, positioned therein. An air curtain having
a uniform velocity profile is set up between first and second cabinets.
Vapor detector probes are positioned in one cabinet downstream of
the air curtain. Detectable vapors carried by an object, such as
a person within the air curtain, are stripped off and transported
to the vapor detectors. By positioning the vapor detectors remote
from the object, a significantly higher number of objects can be
screened using known vapor detection techniques within a given period
What we claim as our invention is:
1. An air curtain device for use in detecting selected vapours
emitted from objects positioned therein, said device comprising
first and second spaced apart cabinets, a vertical wall of said
first cabinet provided with an air discharge grill, a vertical wall
of said second cabinet provided with a corresponding and complementary
air intake grill, said air discharge grill being directly opposite
to said air intake grill, air intake means on said first cabinet
upstream of said air discharge grill, air exhaust means in said
second cabinet downstream of said air intake grill, said air intake
and air discharge means being synchronized to provide a substantially
uniform horizontal flow of air from the first cabinet to the second
cabinet, and vapour detection means located intermediate said air
intake grill and said air exhaust means.
2. The device as claimed in claim 1 wherein said air discharge
grill and said air intake grill comprise identical lattice-work
and wherein the depth of each aperture therein is approximately
four times its cross-sectional dimension.
3. The device as claimed in claim 1, wherein said air intake means
comprises a plurality of vertically aligned and spaced apart fans
in a wall of the first cabinet opposed to said air discharge grill
and said air exhaust means comprises a corresponding number of vertically
aligned and spaced apart fans in a wall of the second cabinet opposed
to said air intake grill.
4. The device as claimed in claim 3, further including at least
one perforated baffle section intermediate said air discharge grill
and said air intake means, and at least one performated baffle section
intermediate said vapour detection means and said air exhaust means.
5. The device as claimed in claim 1 wherein said cabinets are vertically
elongate and are mounted in fixed spaced relationship on a platform,
said first and second elongate cabinets each provided with associated
draft wings, a roof section interconnecting the tops of said first
and second cabinets, and wherein said platform, wings, cabinets
and top section define an individual passageway therethrough.
6. The device claimed in claim 1 including signaling means for
instructing individuals when to enter the device, stand stationary
intermediate the cabinets, and when to egress from the device.
7. The device as claimed in claim 1 further including operator
control means remote from said device for indicating the presence
of a specific vapour emitted from an object positioned in the air
8. The device as claimed in claim 1 wherein said vapour detection
means includes at least three vertically aligned and spaced apart
vapour detectors, the probe tips of each of which terminate centrally
of the air flowing through the second cabinet.
9. The device as claimed in claim 1, wherein each of said first
and second cabinets include separate auxiliary cabinet sections.
BACKGROUND OF THE INVENTION
This invention relates to a novel air curtain device suitable for
use in detecting certain characteristic vapours emitted from objects
Vapours emitted from the more common explosive materials and certain
other contraband substances, unless masked or hermetically sealed,
can be detected even though concealed, using known vapour trace
techniques. When explosives are carried by a person, for example,
the individual's clothing and body becomes rapidly contaminated
by the explosive's vapour. This is also true with respect to personal
effects in luggage when subjected to vapours emitted from a concealed
bomb. Accordingly, vapour detectors or "sniffers" are
an acknowledged security instrument, particularly in view of the
upsurge in terrorist bombings of buildings, aircraft and the like.
Their principal use and application is where a large number of personnel
or other objects must be quickly screened such as is normally encountered
at airport terminals.
One major drawback inherent in vapour detectors used in screening
personnel is the fact that each person must be subjected to individual
search. Personal search is unacceptable to many and is of major
concern to airport supervisors and attendants charged with the responsibility
of orderly and rapid air-traveller and luggage processing.
BRIEF SUMMARY OF THE INVENTION
In accordance with this invention, the detection attributes of
known vapour detectors is retained, notably their ability to detect
certain characteristic trace vapours of selected contraband. The
need for hand-held vapour probes is, however, dispensed with; resulting
in significantly faster vapour detection processing of people or
objects. This is achieved by positioning one or more of the vapour
detectors remote from the object being sampled for trace vapours.
Through the instrumentality of the air curtain, trace vapours enveloping
the object are effectively stripped off and transported in relatively
undiluted form to one or more of the remotely positioned vapour
detectors. As the stripping off and transport of the vapours to
the detectors is finite, the time otherwise taken in manually "sniffing"
a large number of individuals or objects is reduced. Further, fewer
operators or attendants are required and less operator fatigue is
encountered. As the air curtain device of this invention is relatively
innocuous in appearance, another advantage of this invention is
that individuals do not undergo the same type of personal affront
experienced from individual search and indeed, many individuals
would not necessarily be aware of the type of search being undertaken
unless appropriate inquiries were made.
While the air curtain device of this invention may have many different
modes of use, as indicated above, its prime purpose is to screen
personnel, such as air travellers. This is achieved by defining
a walkway between spaced apart first and second cabinets. One vertical
wall of the first cabinet is provided with an air discharge grill
while a vertical wall of the second cabinet directly opposed to
the first contains a corresponding and complementary air intake
grill. Air intake means on the first cabinet upstream of the air
discharge grill draws in ambient air and expels it through the outlet
grill. This expelled air is then drawn in through the air intake
grill of the second cabinet by virtue of air exhaust means located
on the second cabinet downstream of the air intake grill. As the
air intake and air discharge means are synchronized, a continuous
air curtain having a uniform velocity profile is effectively set
up between the opposed grills of the two cabinets. Means for detecting
specific vapours, such as one or more vapour detector probes, are
positioned intermediate the air intake grill and the air exhaust
means and carry out their sample and analyze functions in a known
In operation, when an object or individual is positioned in the
air curtain for a finite period, vapours enveloping the object are
stripped off by the continuous air curtain stream and transported
to the vapour detectors. Based on the principle of laminar flow,
provided the object is not of a size sufficient to destroy the integrity
of the air curtain, stripped vapours are transported to the detector
with a minimum amount of dilution. In screening personnel for explosives'
detection employing vapour detectors, it has been found that air
discharge and air intake grills having a perimeter size of 8 inches
.times. 5 feet are adequate when operating with an air curtain flow
rate of 2 feet per second.
Since a uniform air velocity profile is important, the opposed
grills preferably are identical in lattice configuration in order
to maintain the integrity of the air curtain. Turbulence within
the curtain is further reduced where the depth of each aperture
in the lattice-work is approximately four times its cross-sectional
dimension. With a view to again further enhancing the uniform flow
of air in the air curtain, one or more perforated baffles, such
as expanded metal screens may be positioned upstream of the air
discharge grill and downstream of the air intake grill intermediate
their respective air intake and air discharge means. Where baffles
are employed in the second cabinet, it is preferred to position
the vapour detector probes between the baffles and the air intake
grill so that vapour samples are taken in a relatively quiescent
(as opposed to turbulent) air flow. while not essential, it is also
preferred to locate the vapour detector probes centrally of the
air curtain as it is in this area where the concentration of the
vapours to be detected is at its highest. More than one detector
probe may be required if it is also desirable to monitor the entire
vertical height of the air curtain.
The air intake and air exhaust means should function so as to ensure
or further enhance a uniform air velocity profile of the air curtain.
This may be achieved, for example, by positioning a plurality of
vertically aligned and spaced apart fans in a wall of the first
cabinet opposed the air discharge grill and complementary vertically
aligned and spaced apart fans in a wall of the second cabinet opposed
to the air intake grill.
Transient drafts and external turbulence tending to upset the integrity
of the air curtain may be diminished through the use of vertical
panel sections (draft wings) associated with each cabinet and the
provision of a roof or top section which interconnects the two cabinets.
For portability purposes, the two cabinets may also be mounted in
fixed relationship on a base so that the entire device can be moved
from station to station without re-alignment difficulties.
When the air curtain device of this invention is used in the screening
of personnel, in order to obtain proper vapour stripping and hence
maximum sensitivity, each individual is obliged to remain stationary
in the air curtain for a finite period of time; say two to three
seconds. Accordingly, it is necessary to instruct personnel passing
through the device on the steps required of them. This may be carried
out by means of an attendant on duty instructing each person, or
by the use of barrier gates or other instructional indicia such
as stop and go signals associated with the device that indicate
to the individual when and where he should stop and when he is entitled
The various vapour detector equipment, including the detector controls,
electronics, gas supply and alarm means may be conveniently mounted
within, on or in cabinet sections associated with the two cabinets.
Further, master control equipment and alarm (vapour present) means
may be mounted on a console remote from the air curtain device.
The remote positioning of at least the alarm from the device is
preferred as there is normally a time lag of one to three seconds
from the time the stripped and transported vapours enter the probe
of the detector and the time the detector has had an opportunity
to analyze the vapours so stripped and indicate a positive (vapour
present) response or no response. It is preferred that the attendant
on duty and the console be located and positioned away from the
air curtain device at a point commensurate with the distance one
would normally walk after leaving the air curtain and the time at
which a response (alarm) or no alarm is registered at the console.
If a positive response is registered, the individual can be conveniently
intercepted for further screening.
BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the invention will now be described in
connection with the accompanying drawings wherein:
FIG. 1 is a front perspective view, illustrated in partial cut-away,
of the air curtain device together with the operator's console and
signaling indicia for personnel passing therethrough, and
FIG. 2 is a plan view of the air curtain device illustrating the
laminar flow effect experienced when an individual is positioned
intermediate the opposed cabinets.
DETAILED DESCRIPTION OF THE DRAWINGS
With reference to the drawings, two cabinets, generally designated
by arrows 1 and 2 are mounted on a platform 3 in opposed relationship
sufficiently spaced apart to allow passage of individual 4 therethrough.
The first cabinet, cabinet 1, is defined by four vertical walls
5, 6, 7 and 8, the latter wall also including a front service door.
The second cabinet, cabinet 2, is similarly constructed, having
four vertical side walls 9, 10, 11 and 12; wall 12 also including
a front service door as illustrated. As best seen in FIG. 2, the
first and second cabinets may also advantageously include rear cabinet
sections which in the case of cabinet 1 is defined by vertical walls
5, 6, 7 and 13; the rear cabinet section of cabinet 2 being formed
from vertical walls 9, 10, 11 and 14. Each of rear vertical walls
13 and 14 preferably also include service doors (not shown) the
purpose of which will be apparent hereinbelow. The top and bottom
of cabinets 1 and 2, and the rear cabinet sections thereof, are
closed at their respective tops by top walls 15 and 16 and at their
bottoms, by platform 3.
Ingress ramp 17 and egress ramp 18 are pivotally connected to platform
3 between cabinets 1 and 2. In order to move the air curtain device
from station to station, ingress and egress ramps 17 and 18 are
merely pivoted upwards so that the device may be readily pushed
to a new location on casters 19. In the operating mode, ramps 17
and 18 are swung downwardly in order to define a walkway between
the two cabinets. Wings 40 extending outwardly from the cabinets
tend to protect the integrity of the air curtain from external drafts.
Vertical wall 7 of cabinet 1 is provided with an air discharge
grill 22. In a like manner, vertical wall 9 of cabinet 2 also includes
a corresponding and complementary air intake grill 23 which is directly
opposed and aligned with grill 22. Grills 22 and 23 may be formed
from commercially available honeycomb mesh preferably having a hole
depth approximately four times the hole diameter in order to present
a uniform air velocity profile across the two opposed cabinets 1
and 2 in the direction of arrows 24 as discussed in greater detail
We have found that a grill dimension of approximately 5 feet in
height and 8 inches in width is dimensionally adequate as an air
curtain for the purpose of stripping off vapours from individuals
positioned therein. A space of approximately three feet between
opposed grills 22 and 23 has also been found satisfactory to permit
passage of individuals therethrough without materially upsetting
the flow of air from grill 22 to grill 23.
Air intake means is provided on the first cabinet 1 upstream of
grill 22 and in the embodiment illustrated, comprises a number of
vertically aligned intake screens 25 covering rectangular holes
26 in wall 5. Included with the air intake means, but not illustrated
for the sake of clarity, are air intake fans, (not shown) corresponding
in number and positioned over rectangular holes 26 internally of
cabinet 1. The purpose of the fans is, of course, to draw ambient
air internally of cabinet 1 for discharge through grill 22. A similar
arrangement exists in cabinet 2 whereby vertically aligned discharge
screens 27 cover rectangular holes 28 in wall 11. Air exahust fans
(not shown) are positioned over rectangular holes 28 internally
of wall 11, in order to discharge the incoming air curtain air entering
While the number of rectangular holes 26 and 28 together with their
corresponding fans may vary, we consider a minimum of three, and
preferably five holes in each cabinet to be suitable in setting
up a uniform air curtain flow. The fans in each cabinet are synchronized
so that the ambient air intake at the first cabinet substantially
equals the amount of air exhausted from the second cabinet.
Due to the action of the intake fans and the fact that they are
vertically spaced, ambient air entering the first cabinet through
rectangular holes 26 is relatively turbulent. This is also the case
with the exhaust fans in the area immediately upstream of rectangular
holes 28 in cabinet 2. In order to modulate the air in both cabinets,
one or more perforated baffles, such as baffle 29 in cabinet 1 and
baffle 30 in cabinet 2 are provided. These baffles are positioned
proximate wall 5 donwstream of holes 26 and its associated fan and
proximate wall 11 upstream of rectangular holes 28 and their associated
fans. Since the perforations in the baffles are relatively small,
they set up a relatively uniform air flow velocity profile as it
passes from baffle 29 through grills 22 and 23 to baffle 30.
Located intermediate grill 23 and baffle 30 and extending inwardly
of the second cabinet from wall 10 thereof are a series of vertically
aligned and spaced apart vapour detector probes 31 (two only being
shown in the cut-away illustration of FIG. 1 but there in fact being
three present in the particular embodiment illustrated).
Each probe 31 includes a probe tip 32 which terminates at the mid-point
of the cabinet 2 defined between walls 10 and 12.
From the foregoing, it will be appreciated that when the synchronous
air intake and air exhaust fans are turned on, the flow of air between
the two baffles 29 and 30 including the air curtain traversing grills
22 and 23 is substantially uniform (a flow rate of two feet per
second being considered adequate). With reference to FIG. 2, it
will also be observed that the air flow, designated by arrows 24,
is deflected about the body of the individual 4 in a laminar flow
fashion. The air closest to individual 4 is that air which it taken
in centrally of grill 23 and continues its flow in the central area
of cabinet 2. Thus, detectable vapours enveloping the body of individual
4 are effectively stripped off and transported with a minimum amount
of dilution to the probe tips 32 which, as previously indicated,
are advantageously located centrally of the air-stream so as to
render increased vapour detector sensitivity.
While the rearmost wall of cabinet 1 is effectively defined by
vertical wall 6 which is also the case concerning vertical wall
10 of cabinet 2, the rearmost or auxiliary cabinet sections as previously
described can be used to house the various gas, electrical and mechanical
support components (not shown) necessary to operate the vapour detection
probes and co-ordinate the signaling equipment both for personnel
passing through the device and control of console 38.
In the embodiment illustrated, signalling equipment for the orderly
processing of personnel is provided. Ingress indicator 33 mounted
on top of cabinet 2 alternately displays stop and enter signals,
enter signal 34 only being shown and which informs a person when
to enter the device. Not visually apparent prior to standing on
foot markers 35 located on platform 3 between opposed grills 22
and 23, is egress indicator 36 positioned behind the device which
also alternately displays stop and exit signals, stop signal 37
only being shown. A pressure sensitive switch (not shown) below
foot markers 35 causes enter signal to switch off and to be replaced
by a stop signal thereby informing the next following person not
to enter the device. Through time delay means (not shown) stop signal
37 on indicator 36 remains displayed informing the individual that
he should remain stationary on foot markers 35. This delay, which
is normally two to three seconds, is required in order to permit
the air curtain to strip the vapours enveloping the person on foot
markers 35 and to deliver same to the detectors 31 which are now
in the sample and analyze condition. After the appropriate delay
a momentary audible tone is sounded and at the same time stop signal
37 is switched off and replaced by an exit signal, indicating that
the individual may leave. Approximately three seconds after the
individual has egressed an audible tone of a different frequency
sounds and the stop signal (not shown) of indicator 33 is replaced
by enter signal 34 so that the above process can be repeated.
Operator's console 38 including alarm signal 39 normally is located
behind the device so that if a positive response by the detectors
is recorded, the person leaving the device can be intercepted for
further screening. The orderly monitoring of personnel passing through
the devices can also be manually controlled from the console or
the automatic processing can be interrupted should the occasion
arise. However, it will also be appreciated that other signal control
means for processing personnel may be used without departing from
the spirit of this invention.