Note: Descriptions are shown in the official language in which they were submitted.
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Hreathina Ar~paratus
Field of the Ynvention
The present invention relates to a fan-forced
positive pressure breathing apparatus of the kind in
which filtered air is pumped to a face piece or mask
covering at least the nose or mouth of the wearer, the
air being pumped by means of a fan driven by an electric
motor which is usually battery powered.
Backaround Art
Breathing apparatus of the kind with which the
present invention is concerned is well known and a
variety of different constructions have been proposed and
the advantages and disadvantages of such apparatus are
discussed in many' patent specificat~,ons. Among the
reguirements of a satisfactory apparatus are that it
supplies adequate quantities of air when the user takes a
deep breath which, testing shows, necessitates the supply
of a substantially higher flow rate than normally
anticipated. It is desirable to minimize power
consumption by the motor driving the fan consistent with
the requirements set out above to increase battery life.
It is also highly desirable that the air pressure
within the face piece or mask is never allowed to fall
below the ambient atmospheric gressure. If this happened
air may be drawn into the space within the piece pr mask
drawing environmental contaminants into that space.
The present invention is directed to providing an
alternative form of forced air breathing apparatus that,
at least in pXeferred embodiments, allows these desired
ends to be achieved.
Summary of the Invention
According to the present invention, there is
provided a forced air breathing apparatus comprising a
face piece or mask for covering at least the nose or
mouth of a wearer, a pump unit arranged to supply air to
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a space within the face piece or mask, an electric motor
within the pump unit arranged to drive a fan forming part
Iof the Bump unit, a filter to filter air entering the
face piece ox mask and a valve means for controlling the
flow of air from the pump unit to the face piece or mask
dur~.ng inhalation and from the face piece or mask during
exhalation, the valve means including an air inlet valve
and an air outlet valve, the air outlet valve being
maintained in a closed position during inhalation through
1o the air ~.nlet valve by air pressure from the pump unit
and being opened by exhaled air which also acts on the
inlet valve to prevent the entry of exhaled air to the
pump unit.
The term "face piece or mask" is taken to include any
device covering the nose or mouth of a wearer and adapted
to engage with the wearer's body or clothing around its
edges. It may cover only the mouth or the nose or both
of them. If desired, it may comprise a helmet covering
the whole of the wearer s head.
As used in this specification, the term ~f ilter~ is
taken to include any device for the relrioval Of
particulate and/or gaseous contaminants from the inhaled
air. The particulates may be solid, as in smoke, or
liquid, as in insecticide sprays. where the filter is
adapted to remove gaseous contaminants, the filter may be
in the form of activated carbon or another gaseous
absorbent.
The speed of the motor driving the fan may be
controlled so that the fan runs at a substantially
constant speed. This is in contrast to previous
proposals which have required the speed of the fan to be
accelerated when more air flow is required. It has been
found that operating at constant speed results in a
saving of power consumed as compared With letting the fan
slow down and then speeding it up again.
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In one preferred embodiment of the present invention
the forced air breathing apparatus comprises a face piece
or mask for covering at least the nose or mouth of a
wearer, a pump unit arranged to drive a centrifugal fan,
means for monitoring and controlling the speed of the
motor so that the fan rotates at a substantially constant
speed during its operation, a filter to filter air
entering the face piece or mask and a valve controlling
exhalation or air from the face piece or mask by a user.
1D The apparatus may further comprise a valve
controlling the inlet of air to the pump unit, the valve
being arranged upstream or downstream of the fan and
.being arranged to close when the pressure present within
the breathing apparatus downstream of the fan rises to a
predetermined level. With such an arrangment, it is
easier to ensure that there shall always be a positive
pressure within the face piece or mask at all times thus
avoiding the existence of negative pressure which could
give rise to the entry of contaminated air.
The apparatus according to this invention may
include, downstream of the filter, a device for measuring
the oxygen content of the inhaled air. This device will
preferably provide a warning to a wearer when the oxygen
content of the filtered inhaled air falls below a
2~ predetermined level. In a particularly preferred
embodiment of the invention, the apparatus includes a
source of compressed oxygen or other breathable gas that
can be released into the inhaled air at a rate sufficient
to maintain the oxygen content of the inhaled air above
that predetermined level.
For different applications of the breathing
apparatus, different filter types may be employed. Each
different type of filter alters the apparatus flow
resistance. The demands placed on the breathing
apparatus will also vary with each.filter type as a
filter is progressively used. Tt has been found that
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calibrating the apparatus prior to use such that the
speed and rotation of the fan are set at an optimum base
value results in a saving of power and an increase in
filter life.
The apparatus may further comprise actuable~ control
means adapted to cause the apparatus to undergo a
calibration phase such that the speed of rotation of the
fan is set at a pre-determined optimum base value
relative to the operating conditions then prevailing in
to the apparatus. The base value is preferably maintained
substantially constant during any one period of operation
of the apparatus or until the apparatus is recalibrated.
In a preferred embodiment, the apparatus includes an
electronic data processing means wh~.ch monitors and
controls the speed of the motor so as to ensure adequate
air flow at the mask of the apparatus.
In one embodiment, the actuable control means would
be manually operated by a user of the apparatus. In this
embodiment, the actuable control means would inolude the
~o electronic data processing means with the user entering
parameters relevant to the filter type and/or the flow
resistance so as to set the optimum speed of the fan
prior to use.
In another embodiment, the actuable oontrol means
would automatically set the apparatus to undergo a
calibration phase. One means of automatic operation would
involve the parameters of the filter type being coded
onto the filter such that the details are detected by the
electronic data processing means which automatically
3U adjust the flow of air through the apparatus. The
transmission of the coded information to the eleotronic
data processing means could be by optical, electrical or
magnetic transfer.
A second and more desirable means of automatic
operation would involve use of a pressure sensor and/or
f low measurement apparatus, each under the control of the
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electronic data processing means. The pressure sensor
and/or flow meter would preferably be located proximate,
and downstream of, the filter of the apparatus such that
flow arid pressure drop are automatically measured with
5 detected values of air flow and pressure being fed to the
electronic data processing unit. The electronic data
processing unit would then automatically calculate the
appropriate speed of rotation of the fan given the
measured parameters.
In one embodiment, the pressure sensor comprises a
silicone pressure transducer. In a preferred embodiment,
the pressure sensor comprises a flexible membrane
arranged to flex with changes in pressure, an ultrasound
transmitter arranged to direct ultrasound at the
membrane, an ultrasound xeceiver arranged to detect
ultrasound reflected from the membrane, and an analyzing
means, the analyzing means being capable of determining a
parameter based on the transit time of the ultrasound
between the transmitter, membrane and receiver and
calibrated so as to provide an indication of air pressure
to the electronic data praccssing means.
To compensate for changes in the transit time of the
ultrasound between the transmitter, membxane and receiver
caused by temperature variations, there is preferably .
located proximate the pressure sensor a temperature probe
in communication with the analyzing means, the analyzing
means applying a compensation algorithm to the transit
time in accordance with the measured temperature.
In anothex embodiment, the flow measurement
3o apparatus comprises an air flow restrictor such as an
orif ice plate or mesh and a pressure sensor adapted to
measure the change in pressure across the restrictor.
In another embodiment, the flow measurement
apparatus comprises a pressure sensor adapted to measure
the change in pressure between the pump unit and the face
piece or mask resulting from one or more air flow
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restrictors between the pump unit and face piece or mask.
The air flow restrictor preferably comprises an air
transfer hose which allows flow of air between the pump
unit and face piece or mask.
In a further embodiment, the flew measurement
apparatus comprises an ultrasound transmitter and a
ultrasound receiver adapted to respectively transmit and
detect ultrasound travelling along a portion of the air
transfer hose. The flow rate is directly proportional to
the time shift of the ultrasound travelling down the
hose. one advantage of this method is that it places no
flow restrictions on the air flow in the apparatus.
Tn a still further embodiment, the flow measurement
apparatus comprises a thermistor placed in the air flow
and heated to a temperature greater than ambient
temperature, the flow rate being proportional to the
cooling effect of the air flow on the heated thermistor.
Due to hygienic and safety reasons, the mask is
preferably washed after each use. For these reasons it
is not desirable to have electrical systems, or other
apparatus vulnerable to breakage, in the mask_
In another preferred embodiment, the apparatus
further comprises a performance monitoring means for some
or all of the parts which provides at least one signal
that informs the wearer of the condition of some or all
of the parts, wherein the signal is generated externally
to the face piece or mask and is fed to the face piece or
mask for detection by a wearer.
In one embodiment, the performance monitoring means
includes a pressure transducer which detects the air
pressure within the apparatus, the pressure transducer
being preferably located proximate the fan. The output
from the pressure transducer is preferably fed to an
electronic data processing unit within the performance
monitoring means. Should the air pressure fall below a
preset safe minimum level, at least one Warning signal
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is generated by the electronic data processing unit for
detection by the wearer.
In another embodiment, the performance monitoring
means monitors the condition of the power source, the
filter and/or the fan/motor unit. The power source
preferably aompxises a rechargeable battery. Should
battery charge, as measured by a voltmeter, fall below a
15
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pre-set safe level for operation of the apparatus, the
electronic data processing unit preferably detects this
occurrence and generates a warning signal for detection
by the wearer. Filter condition is preferably monitored
by an air flow meter/pressure transducer that monitors
the flow resistance of the filter. Should the resistance
exceed a pre-set safe maximum level, the electronic data
processing unit detects this occurrence and generates a
warning signal for detection by the wearer. Fan/motor
unit condition is preferably monitored by an air
flow/pressure transducer and a voltage/current transducer
that monitors the performance rate of the fan/motor unit.
Should the performance rate fall below a pre-set safe
minimum level, the electronic data processing unit
detects this occurrence and generates a warning signal
for detection by the wearer.
The warning signal is preferably a light source
and/or audible tone. The light source is preferably a
light emitting diode (LED). The light from the light
emitting diode is preferably transmitted to the face
piece or mask by optical fiber. The optical fiber is
preferably connected to the mask with a fitting which
allows straightforward detachment of the optical fiber
from the mask.
The audible tone is preferably transmitted to the
face piece or mask by an air hose serving as a sound
pipe. The air hose is also preferably detachable from
the head piece, face piece or mask.
In a further embodiment, the fan unit of the
respirator apparatus includes a pressure transducer. The
pressure transducer is preferably in communication with
the space within the head piece, face piece or mask via
at least one hose so as to allow measurement of the
pressure in the space within the face piece or mask.
Preferably, the apparatus is arranged so as to allow
measurement of pressure at a number of locations within
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the apparatus. Preferably, a plurality of hoses from
different parts of the apparatus are in communication
with the pressure transducer with the electronic data
processing unit controlling from which location the
pressure measurement is being taken at any one time. In
one embodiment, one hose is connected to a reference
port, preferably atmospheric pressure, with the values of
pressure for other locations measured as a ratio of the
pressure measured at the reference port.
Ready removal of the optical fiber, pressure
communication hoses and/or air hoses from the mask
ensures easy cleaning of the mask prior to and/or after
use.
The positive air pressure breathing apparatus
according to this invention preferably operates at a low
pressure but at a relatively high flow rate. In
preferred embodiments the apparatus is capable of
delivering at least 150 litres of air per minute,
preferably 300 litres of air per minute, and more
preferably at least 500 litres of air per minute, to a
wearer. In preferred embodiments the supply pressure of
air to the air inlet valve admitting air to the face
piece or mask is between zero and 10 mBar, more
preferably no more than 6 mBar, above ambient reference
pressure. It is also preferred that the fan in the pump
unit produces a pressure in this range. It is possible,
however, to provide a regulator between a pump unit
producing air at a higher pressure and the value means
associated with the face piece or mask. In this case the
pump unit will supply air at a pressure of less than 1
Bar, preferably less than 100 mBar, and more preferably
less than 20 mBar. At these low pressures hose diameters
must be so chosen as to avoid undue flow restrictions
that would cause large pressure drops in the system.
CA 02196166 2000-11-20
Brief Description of the Drawinqs
In order that the nature of the invention may be
better understood, preferred forms thereof are
hereinafter described by way of example with reference to
5 the accompanying diagrammatic drawings, in which:
Figure 1 is a diagrammatic drawing of those parts of
the apparatus with which the present invention is
concerned, in the configuration adopted during the period
in which air is being inhaled by the user;
l0 Figure 2 is a view similar to Figure 1 showing the
apparatus in the configuration adopted when air is being
exhaled by the user;
Figure 3 is a view in cross-section of one form of
exhaust valve according to the invention;
Figure 4 is a plan view from below of the valve
shown in Figure 3;
Figure 5 is a view in cross-section through another
form of exhaust valve according to the invention,
Figure 5(a) showing the valve during inhalation,
Figure 5(b) showing the valve in a stable closed
condition, and
Figure 5(c) showing the valve during exhalation;
Figure 6 is a view in cross-section through a
further form of exhaust valve according to the invention,
Figure 6(a) showing the valve during inhalation,
Figure 6(b) showing the valve in a stable closed
condition, and
Figure 6(c) showing the valve during exhalation;
Figure 7 is a diagrammatic drawing of a still
further form of the apparatus with which the present
invention is concerned,
Figure 7(a) showing the apparatus during inhalation,
and
Figure 7(b) showing the apparatus during exhalation;
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Figure 8 is a diagrammatic drawing of yet another
form of apparatus in which the present invention is
concerned,
Figure 8(a) showing the apparatus during inhalation,
and
Figure 8(b) showing the apparatus during exhalation;
Figure 9 is a schematic view of one embodiment of
the respirator apparatus according to the fourth aspect
of the present invention; and
Figure 10 is a schematic view of one embodiment of a
user interface for a respirator apparatus according to
the fifth aspect of the present invention.
Description of the Specific Embodiments
The apparatus shown in Figures 1 and 2 consists of a
pump unit 10 enclosing an air space and an electric motor
11 driving a centrifugal fan 12. In addition to the
parts shown there is a source of power for the motor,
usually a rechargeable battery, and in addition a motor
speed control unit of conventional construction. This
unit monitors the speed of rotation of the fan 12 and
controls the speed of the motor to cause it to operate at
a substantially constant speed irrespective of whether
air is being inhaled or exhaled by the user.
Air is drawn into the pump unit 10 through a
conventional filter 13. The entry of air from the filter
is controlled by the valve member 14 associated with the
bellows 15 which closes the valve during exhalation of
air as shown in Figure 2 and which is lightly biased to
the open position by means of the spring 20 as shown in
Figure 1. During the inhalation of air as illustrated in
Figure 1 the valve 14 is displaced by the spring 15 and
the depression within the pump unit to allow air to enter
the pump unit.
Means may be provided for adjusting the pressure at
which the valve 14 closes. It is desirable to keep this
as low as possible and for the valve to be arranged to
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open only for a time sufficient to allow the required
amount of air to enter after which the valve closes. The
system is balanced with the valve acting as a pressure
regulator to minimize pressure fluctuations in the pump
unit as much as possible to ensure a more or less
instantaneous supply of air from the fan to the user as
soon as inhalation commences.
The pump unit is connected by means of the duct 16
to an exhaust valve shown at 17. The duct 16 splits into
two parts; a duct 18 which leads via a valve member 19 to
the face piece or mask (20a) and also to an exhaust
outlet 21 which during inhalation is closed by the valve
member 22 which is lightly biased to the closed position
by the spring 23 as shown in Figure 1. In certain
embodiments of the invention the valve 22 could be
replaced by a simple spring loaded exhalation valve.
The second branch 24 of the duct 16 leads to the
rear of the valve member 22 which tends to maintain the
valve in a pressure balanced condition.
The flow of air during inhalation is illustrated by
the arrows shown in Figure 1. Air is drawn in through
the open valve 14 to the fan 12 which generates a
pressure to produce an air flow through the ducts 16 and
18 to the face piece or mask worn by the user. It will
be seen that the valve 19 is maintained open by the air
pressure on it and air flows freely to the user. The
pressure of air in the duct 24 acts on the back of valve
22 to reinforce the action of the spring 23 and keep the
valve closed.
The configuration of the apparatus during exhalation
is shown in Figure 2 in which the valve 14 is closed.
The valve 19 is also closed due to exhalation of air by
the user. The fan 12 which is maintained at a constant
speed of rotation by the motor 11 is operating in a
stalled condition and the pressure generated by it is not
sufficient to open the valve 19 against the pressure of
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exhaled air. It does, however, apply pressure to the
rear of the valve 22 but at a lower level than the
exhalation pressure, thus allowing the valve 22 to be
held open. Exhaled air can escape from the exhaust
opening 21.
Whereas the apparatus is shown in a purely
diagrammatic manner in Figures 1 and 2, Figures 3 and 4
show in a more realistic manner one form of exhaust valve
construction corresponding in function to the exhaust
valve 17 shown in Figures 1 and 2. In this construction
the duct 25 corresponds to the duct 16 in Figures 1 and
2, a pair of one-way valves 26 correspond to the valve
member 19 of Figures 1 and 2, and a pair of outlet
apertures 27 correspond to the duct 18 of Figures 1 and 2
providing a connection to the face piece or mask. Thus,
during inhalation, air from the pump unit enters the duct
25, passes through the valve 26 and is supplied to the
face piece or mask through the outlet 27.
Within the center of the outlet valve is a diaphragm
valve 28 lightly loaded by a spring 29 onto a seating 31.
This valve has a central hollow stem 32 movable with the
diaphragm. This has air inlet apertures 33 at its lower
end and an air outlet 34 at its upper end. The diaphragm
valve 28 corresponds to the valve 22 of Figures 1 and 2.
During exhalation air enters through the air inlets
27. The exhaled air exercises pressure on the diaphragm
valve 28 and causes it to open against the spring 29.
Air then passes the diaphragm of valve 28 and vents to
atmosphere through the one-way valves 35 at the top of
the casing. The valves 35 which prevent the ingress of
contaminated air in the event of fan failure are not
absolutely essential to the operation of the system and
may be omitted.
The exhaust valve shown in Figures 3 and 4 has
features not shown in Figures 1 and 2 in that when the
hollow stem 32 is in the position shown in Figure 3, air
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under pressure from the pump unit can enter the apertures
33 and exert pressure on the upper surface of the
diaphragm valve 28, reinforcing the action of the spring
29, and the situation is similar to that shown in Figures
1 and 2. Once, however, the diaphragm 28 moves upwardly
it carries the member 32 with it. This has the effect of
shutting off the air inlets 33 and opening the air outlet
34 thus releasing any air pressure above the diaphragm 28
through the one-way valves 35.
The valve 40 includes an air inlet duct 41 connected
to a source of positive air pressure (not shown), a first
valve 42, a face mask 43 covering the mouth and nose of a
wearer (as is shown in Figure 5(a)), a second valve 44,
and a discharge aperture 45 for the discharge of exhaled
air to atmosphere.
The first valve 42 serves to admit air from the
inlet duct 41 into the face mask 43 when the system
pressure in the inlet duct 41 exceeds the pressure in the
face mask 43. When the pressures are equal the value 42
closes.
The second valve 44 serves to permit the passage of
exhaled air from the face mask 43 through the discharge
aperture 45 to atmosphere. The valve 44 comprises a
diaphragm which is exposed on a first face 46 to the
inlet duct 41 and the air pressure therein. A second
face 47 of the diaphragm of valve 44 is arranged to bear
against a valve seat 48 for the second valve 44. The
area of the second face 47 of the diaphragm within the
area defined by value seat 48 is exposed, when the valve
is closed, to the pressure within the face mask 43. The
remainder of the second face 47 of the diaphragm will be
exposed to atmospheric pressure through discharge
aperture 45 when the valve 44 is closed.
In operation air will flow from inlet duct 41
through valve 42 into the face mask 43 until it is equal
in pressure to that in the inlet duct 41. The valve 42
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will then close. If the wearer now exhales the pressure
in the face mask 43 will rise. Once the rise is
sufficient to overcome the force holding valve 44 in a
closed position that valve will open and air will
5 discharge from the face mask 43 through valve 44 and
discharge aperture 45 to atmosphere.
The force holding the valve 44 in a closed position
is the difference between the pressure on the first face
46 and the second face 47. As the pressure applied to
10 the diaphragm from the inlet duct 41 and the face mask 43
will initially be equal, it can be seen that the force
holding the valve 44 closed is the difference between
atmospheric pressure on that part of the second face that
lies outside the valve seat 48 and the inlet duct
15 pressure over a similar area. As this area is small
relative to the area of the diaphragm which lies within
the area defined by valve seat 48, even a small rise in
pressure within the face mask is sufficient to open the
outlet valve 44. As the area is small even a substantial
increase in system pressure within the inlet duct will
not raise greatly the exhalation pressure required to
open the second valve 44.
The arrangement shown in Figures 6(a) to 6(c) is
essentially similar to that described with reference to
Figures 5(a) to 5(c) and similar parts are given the same
numeric designation. In this embodiment the first valve
42 is disposed within the membrane of the second valve
44. The valve works in the manner described with
reference to Figures 5(a) to 5(c).
The arrangement shown in Figures 7(a) and 7(b) is
similar to the arrangement described with reference to
Figures 1 and 2 with two major exceptions. The first
exception that the valve 40 of Figures 6(a) to 6(c) has
been substituted for valve 17 of Figures 1 and 2. The
second exception is that the filter 13 is moved from in
front of the fan 12 to behind the fan 12. The pressure
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controlling the valve 14 is drawn from a duct 60 linking
the filter 13 with the valve 40. In this way the opening
and closing of the valve 14 more closely reflects the
changes in pressure due to the breathing by a wearer due
to inclusion of the pressure drop over the filter in the
regulation.
Figures 8(a) and 8(b) show fan-forced positive air
pressure breathing apparatus according to this invention.
The arrangement is similar to the arrangement described
with reference to Figures 7(a) and 7(b) and similar parts
are given the same numeric designation. In this case the
fan operates at a high pressure and feeds high pressure
air to a regulator 51. Air from the regulator 51 flows
through hose 53 to valve 40.
A positive air pressure respirator is generally
shown as 110 in Figure 9. The apparatus includes a pump
unit in which is situated an electric motor 111 driving a
centrifugal fan 112. In addition to the above parts
shown there is a source of power for the motor 111,
usually a rechargeable battery (not depicted), and a
motor speed control unit under microprocessor control
115.
Air is drawn into the respirator 110 through a
filter 113, passes through the fan 112 and exits the
apparatus 110 via the mask 114. The mask 114 is adapted
to completely cover the mouth and nose of a wearer and is
adjustable so as to fit snugly to the contours of the
face of the wearer.
The microprocessor control 115 in the embodiment
depicted monitors input from a pressure transducer 116
and a flow meter 117 and is thereby able to ascertain the
flow resistance of the filter 113 being employed. In
those cases where flow resistance is high, the
microprocessor control 115 will note this and set the
speed of rotation of the fan 112 at a higher level to
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compensate, thereby ensuring that adequate flow of air is
available at the mask 114 on inhalation by the wearer.
In operation, the microprocessor control 115 will
automatically undertake a measure of flow resistance and
automatically adjust the speed of the fan 112 to the
necessary level.
A positive air purifying respirator is generally
shown as 210 in Figure 10. The apparatus includes a pump
unit in which is situated an electric motor driving a
centrifugal fan, a power source, usually a rechargeable
battery, and a motor speed control unit under
microprocessor control (all not depicted). Air is drawn
into the respirator 210 through a filter, passes through
the fan and exits the apparatus 210 through an air hose
211 and mask 212. The mask 212 is adapted to completely
cover the mouth and nose of a wearer and is adjustable so
as to fit snugly to the contours of the face of the
wearer.
Performance of the apparatus 210 is monitored by a
performance monitor located within the pump unit. The
performance monitor controls a pressure transducer
located proximate the fan, a flow meter located proximate
the filter, a voltmeter monitoring the charge of the
battery and a pressure transducer 213 located in the
apparatus 210 which measures the pressure in the space
within the mask 212. The pressure transducer 213 is in
communication with the space within the mask 212 via a
flexible hose 214. The hose 214 is preferably connected
to the mask 212 with a fitting which allows ready removal
of the hose 214 after use of the apparatus 210.
Should air pressure either at the fan or within the
mask 212, air flow or battery charge fall below a pre-set
low level, the performance monitor issues a warning
signal to the wearer.
The warning signal comprises both an audible tone
and an indicator light. The audible tone is generated by
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a speaker 215 within the apparatus 210, with the tone
transmitted through the air transfer hose 211 to the mask
212. The light source is generated by a light emitting
diode (LED) 216 with the light transmitted to the field
of view of the wearer in the mask 212 by an optical fiber
217.
Both the optical fiber 217 and air hose 211 are
connected to the mask 212 by fittings which allow ready
removal of these items from the mask 212 prior to it
being cleaned.
