Communication system for use in hazardous confined areas

A communications system for use by workers in a confined hazardous working location includes a transmitter that is carried by the worker in the hazardous area. The transmitter is capable of sending either an alarm signal or a check-in signal to a centrally located monitoring and control station. The monitoring and control station includes a receiver for receiving the signal from the transmitter and further includes an alarm that is activated upon receipt of an alarm signal from the transmitter. The receiving unit further includes a timer that automatically activates an alarm signal upon the expiration of a predetermined amount of time. The timer in the receiver is initialized by receipt of a check-in signal from the transmitter. The transmitter includes a warning subsystem that alerts the worker of the impending expiration of time on the receiver timer to permit the worker to check in and reinitialize the receiver timer, thereby eliminating false alarms.

BACKGROUND OF THE INVENTION 
This invention relates to communications systems and more particularly 
relates to a communication system for use in hazardous confined areas. 
There exist several situations in which a worker must enter a confined 
space in order to perform some work. One example of such a work situation 
is in the airplane industry, where workers must climb inside the fuel 
tanks located in the wings of an aircraft in order to clean and seal the 
inside of the fuel tanks before they are filled with fuel. Generally, the 
solvents which are used in cleaning these fuel tanks give off fumes which 
are toxic in varying degrees. 
State and federal governments are enacting strict safety codes dealing with 
work in hazardous areas in order to protect workers from potential or 
actual dangers. For example, a typical regulation dealing with a situation 
such as the hazardous job of cleaning out aircraft fuel tanks calls for a 
lifeline to be attached to the worker who is inside the fuel tank. The 
lifeline is then run outside the confined space and a second worker is 
assigned to tend the lifeline so that in case of trouble the second worker 
can pull the first worker out of the hazardous situation by means of the 
lifeline. 
A system involving lifelines and tenders requires that an extra person be 
placed on the job and results in a sharp increase in costs and inefficient 
use of personnel. It is desirable, therefore, to provide some other means 
for keeping in touch with a worker in a hazardous work area that does not 
involve such inefficient and costly measures. 
Several systems have been devised in the prior art for dealing with such 
situations. One such system is shown in U.S. Pat. No. 3,588,858 to Demuth. 
In the Demuth system, a safety alarm system becomes activated when the 
body of a worker assumes a position other than a normal working position. 
The activation is provided by means of a position-sensitive switch 
attached to a radio transmitter which broadcasts a signal depending upon 
the position of the person wearing the transmitter. For example, so long 
as the worker is standing upright, no alarm is transmitted, however, 
should something happen to cause the worker to lose consciousness and 
fall, the change in position of the worker to a substantially horizontal 
position would cause the position-sensitive switch to activate the 
transmitter and send an alarm which in turn would be monitored by other 
personnel who could send help to the scene. There are certain 
disadvantages to use of a position-sensitive switch activated transmitter. 
The most significant one is that such a system will not work in an area 
where the normal working position cannot be predicted. For example, during 
the operation of cleaning an aircraft fuel tank mentioned above, the 
worker may be in a standing position at one point, crouching at another, 
sitting, and possibly even kneeling or lying down during his efforts in 
cleaning the inside of the tank. Therefore a position-sensitive switch 
would not work since the worker could be in several different positions 
and still not be in any danger. 
Systems have also been devised using vapor-sensitive switches which 
activate an alarm transmitter when the buildup of vapors within the space 
reaches a certain level. The problem with a system based on vapor 
concentration is that there are several different kinds of solvents and 
several different kinds of vapors used with varying degrees of toxicity 
and varying allowable concentrations so that the vapor sensing range of 
the switch would have to be adjusted each time a different solvent was 
used and possibly even between operations if one solvent was used 
initially and then a second solvent was used for a second cleaning, for 
example. 
It is also possible to monitor the vital signs of the worker such as 
breathing rate, heart rate, blood pressure, pulse, however, the systems 
which are capable of monitoring vital signs are expensive and generally 
the probes which are attached to the worker to make such measurements are 
complicated and difficult to attach. 
It is therefore an object of the present invention to provide a 
communication system that can be used by workers in hazardous areas to 
both automatically monitor their well-being during their exposure in the 
hazardous area and also to allow them to summon assistance from the 
outside if need be. 
It is a further object of this invention to provide such a communication 
system in which an alarm is automatically activated after a certain period 
of time has elapsed if the worker has not checked in with a command 
station prior to the lapsing of that time. 
It is a further object of this invention to provide such a communication 
system in which the worker is alerted of the pending expiration of the 
check-in time period to prevent false alarms from being sent. 
It is another object of this invention to provide such a communication 
system which can be utilized in connection with several workers in several 
locations simultaneously. 
It is another object of this invention to provide such a communications 
system that is relatively inexpensive to manufacture and operate and 
simple for the worker to use. 
SUMMARY OF THE INVENTION 
In accordance with the above-stated objects, a communications system for 
use in a confined hazardous area is disclosed including a transmitter that 
is capable of selectively transmitting either a first signal or a second 
signal to a receiving means. The receiving means produces a first alarm 
signal in response to reception of the first signal and produces an 
initialization signal in response to the reception of the second signal. A 
first timer means is coupled to the receiver means and is initialized by 
the initialization signal from the receiver means. The first timer means 
is adapted to produce a time out signal upon expiration of a predetermined 
period of time after initialization. An alarm means is coupled to the 
first timer means and the receiver means. The alarm means preferably 
produces both an audible and visible alarm in response to either the time 
out signal or the first alarm signal. 
Preferably, the communication system also includes a manually actuatable 
reset means that selectively produces either a reset signal or a silence 
signal. The manually actuatable reset means is coupled to the alarm means 
and reception by the alarm means of the reset signal terminates the 
audible and visible alarms whereas reception by the alarm means of the 
silence signal terminates the audible alarm while maintaining the visible 
alarm. 
Further, the communication system preferably includes a second timer means 
associated with the transmitter. The second timer acts as a reminder to 
the worker carrying the transmitter to transmit the second signal to 
initialize the first timer means. The second timer is initialized by 
transmission of the second signal by the transmitter. Upon expiration of a 
predetermined time after initialization, the second timer activates a 
buzzer also associated with the transmitter to alert the worker that it is 
time to activate the transmitter for transmission of the second signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In accordance with the above-stated principles and objects, a 
communications system suitable for use in a confined hazardous area in 
order to account for the safety and well-being of workers within that 
hazardous area will be described with particular reference to the use of 
the system in conjunction with the construction and maintenance of an 
aircraft. Although the system will be described in the environment of an 
aircraft for use by workers who are cleaning the fuel tanks located within 
the wings and tail section of the aircraft, it should be understood that 
the system will work equally well in any situation in which workers 
perform individually within a confined hazardous area remote from other 
workers. 
Referring to FIG. 1, a communications system made according to the 
principles of the present invention includes a plurality of transmitter 
assemblies, one assigned to each of the hazardous work areas to be 
monitored. A typical transmitter assembly 10 includes a manually 
actuatable check-in button 12 and a manually actuatable alarm button 14 
coupled to an encoder 16 that develops a signal in response to actuation 
of either the check-in or alarm button, and encodes on the signal 
information that indicates whether the check-in button or alarm button has 
been pressed. The encoder 16 is coupled to a transmitter 18 which sends 
the encoded signal to a centrally located control and monitoring station 
20. The control and monitoring station 20 includes a plurality of receiver 
assemblies with a discrete receiver assembly matched to each transmitter 
assembly. A typical receiver assembly 22 matched to the transmitter 
assembly 10 includes a receiver 24 that receives the message signal 
transmitted by the transmitter 18 and decodes it to determine whether the 
signal was initiated by depression of the check-in button 12 or the alarm 
button 14. If the signal is one indicating that the check-in button was 
pressed and that the worker is in good condition, a check-in signal is 
sent by the receiver 24 to a display assembly 26 to light a green light or 
other suitable indicator to indicate that the worker has checked in and is 
okay. If the signal received by the receiver is one initiated by 
depression of the alarm button 14, then the receiver 24 sends an alarm 
signal to the display unit 26 that lights a red light or other suitable 
indicator on the display unit indicating an alarm condition. In the case 
of an alarm, the receiver 24 also sends an alarm signal to an audible 
alarm means 28 and a visible alarm means 30 associated with the control 
and monitoring station 20 and preferably common to all of the receiver 
assemblies. A manually actuatable reset assembly 32 is included in the 
control and monitoring station and is coupled to the audible alarm means 
and visible alarm means so that in one instance the reset assembly can be 
actuated to send a silence signal to the audible alarm means to silence 
the audible alarm while the visible alarm means continues to indicate, so 
that later occurring alarms from other transmitter assemblies in other 
work locations are not masked by the first alarm that is received. The 
reset assembly 32 can also be actuated to send a reset signal to both the 
visible alarm means and the receiver assembly 22 to remove all alarm 
indications when the problem that necessitated transmitting the alarm 
signal has been corrected. 
The receiver assembly 22 also includes a first timer 34 coupled to both the 
receiver 24 and the display assembly 26. The first timer 34 is initialized 
by an initialization signal produced by the receiver 24 upon reception of 
a check-in signal from the transmitter 18. The first timer then monitors a 
predetermined time period, in the preferred embodiment 30 minutes. Upon 
expiration of the 30 minutes from the initialization the first timer sends 
a time out signal to the display unit 26 to light an amber light or other 
suitable indicator signifying that a check-in signal has not been received 
within the last 30 minutes. The first timer at the same time also sends a 
time out signal to the visible alarm means and the audible alarm means, 
actuating those two alarm systems in the same manner that they are 
actuated by the alarm signal from the receiver 24. The first timer and 
alarm subsystem insures that should anything happen to the worker in the 
remote hazardous location that prevents him from operating the alarm 
button on the transmitter assembly, that a time period no longer than the 
time set by the timer, for example, 30 minutes, goes by without 
notification to the monitoring personnel that some trouble has occurred. 
In order to prevent false alarms caused simply by forgetfulness on the part 
of the worker in failing to send a check-in signal at the required 
intervals to prevent an alarm from occurring, the transmitter assembly 10 
is equipped with its own second timer 36 that is initialized in response 
to depression of the check-in button 12 and that is set for a time period 
shorter than the time set in the receiver assembly's first timer 34, for 
example 25 minutes. The second timer 36 in the transmitter assembly 10 is 
coupled to an attention-getting device, for example, a buzzer 38 included 
in the transmitter assembly. Upon expiration of the time period set in the 
second timer 36, the second timer 36 sends a signal to the buzzer 38 
causing the buzzer to sound, thereby alerting the worker that it is time 
to check in. Upon depression of the check-in button 12, the second timer 
36 is reset and the buzzer 38 is deactivated for another predetermined 
length of time. 
In the preferred embodiment the signal sent from the transmitter 18 to the 
receiver 24 is an RF signal and the "check-in" or "alarm" condition is 
digitally encoded on the RF carrier. While the preferred embodiment uses 
RF signals, it would also be possible to use ultrasonic or other types of 
carrier signals with proper equipment to encode the necessary information 
onto the carrier. Further, while the RF signal in the preferred embodiment 
is digitally encoded with the message information, any other type of 
modulation which would achieve similar encoding could be used, such as 
frequency modulation of a carrier signal. 
FIGS. 2, 3, 4 and 5 illustrate one structural embodiment of the 
communication system functionally depicted in FIG. 1. Referring now to 
FIGS. 2, 3 and 4 a control console 40 includes an upper portion 40a and a 
lower portion 40b and houses the control and monitoring station. A control 
panel 42 forms the upper wall of the upper portion 40a of the control 
console. The control panel 42 has a plan view outline of an aircraft 43 
depicted thereon. The control panel could alternatively have other 
pictures or no picture depicted thereon, depending on the environment in 
which the communications system was being used. In the illustrated 
embodiment, for use in an aircraft environment, a plurality of receptacle 
and indicator units 44 are mounted on the panel 42 arranged at each 
location of a hazardous work area, for example, on the wings and fuselage 
of the aircraft. Each receptacle and indicator unit includes an indicator 
light group including a red indicator light 46, a yellow indicator light 
48 and a green indicator light 50. The receptacle and indicator assembly 
44 is shown in detail in FIG. 4. The red light 46 has the legend "ALARM" 
printed above it. The green light 50 has the legend "CHECKED" marked above 
it and the yellow light 48 has the legend "WARNING" marked above it. 
A rectangular aperture is formed in each receptacle and indicator assembly 
44 to accommodate entry of a transmitter unit 52 into transmitter 
receptacles 54 one of which is mounted in register with each aperture in 
each receptacle and indicator unit extending downwardly from the control 
panel 42. Each receptacle and indicator unit also includes an audio 
silence switch 56 and an alarm reset switch 58 mounted adjacent the 
indicator lights. The function of theswitches 56 and 58 will be described 
below. 
The receiver assembly electronics are housed in an electronics cabinet 60 
mounted in the lower section 40b of the control console and coupled to the 
control panel indicator lights by suitable cables. A common antenna 62 is 
mounted on the upper portion 40a of the control console and extends 
upwardly above the console. The antenna is simultaneously coupled to all 
of the receivers. In the illustrated embodiment each of the receivers 
comprises a printed circuit board (not shown) mounted within the 
electronics cabinet 60. The signal received by the antenna 62 is routed to 
all the receiver circuit boards simultaneously. The signal from each 
transmitter is coded to identify it as originating from a particular 
transmitter. Therefore, although all the receiver boards receive the 
signal, only that one receiver board that is keyed to the particular coded 
signal from a specific transmitter is actuated by the signal. 
Alternatively, a single receiver circuit could be used that is coupled to a 
plurality of display units. In this form, the signal from the transmitter 
would necessarily be encoded with transmitter-identifying information. The 
single receiver circuit would be capable of decoding the signal to 
determine which transmitter was sending the signal. Upon identifying the 
transmitter, the receiver would then activate the display unit associated 
with that particular transmitter and work station. 
A strobe light 64 preferably of either red or yellow color performs the 
visible alarm function and is mounted on one end of a rod 66 which in turn 
is attached at its other end to the lower section of the control console 
40. The strobe light 64 provides a visual indication of an alarm condition 
in which help is sent to the worker at the hazardous working location and 
is coupled to the receiver electronics by a suitable cable. Preferably the 
rod 66 is long enough to place the strobe light 64 some distance above the 
console at a height that makes it easily visible not only from the area 
immediately adjacent the control console, but also from an area out to a 
substantial perimeter surrounding the control console. The audible alarm 
function is performed by a bell 68 or other suitable audible 
signal-producing means mounted on a side panel of the lower section of the 
control console and also coupled to the receiver electronics by a suitable 
cable. 
A typical transmitter unit 52 is shown in FIG. 5 and preferably comprises 
case 70 of a size comparable to a standard walkie-talkie easily held by a 
person or clipped to the belt without an excess amount of weight having to 
be carried around with the worker while performing his job function. A 
check-in button 72 is mounted on the top of the transmitter unit and is 
recessed within a cylindrical guard 74 to prevent accidental actuation of 
the check-in button. An alarm button 76 is mounted on a side panel of the 
transmitter unit and is recessed within a cylindrical guard 78 similar to 
the guard 74 surrounding the check-in button. A conventional antenna 80 is 
mounted on the top panel adjacent the check-in button 72 and extends 
outwardly from the transmitter unit 52. 
For purposes of system integrity, it is preferable that the control console 
contain a battery charging system which acts to maintain a full charge on 
the batteries of the transmitter when the transmitter is placed into its 
storage receptacle in the control console. Similarly, to prevent 
unnecessary or false alarms and to also prevent unnecessary current drain 
from the battery, circuits are provided to disable the transmitter timer 
and buzzer when the transmitter is located in its receptacle. A four-pin 
male electrical connector 82 is located at the bottom of the transmitter 
unit. The four-pin male connector mates with a four-pin female electrical 
connector 84 mounted at the bottom of the transmitter receptacle 54 
mounted in the control console 40. Two of the male pin connectors are 
connected internally within the transmitter unit so as to connect the 
battery within the transmitter unit to a battery charger within the 
receiver electronics cabinet when the transmitter unit is mounted in its 
associated receptacle during periods of nonuse. The other two pins of the 
male connector cooperate with the matching pins of the female connector to 
form a circuit to disable the reminder buzzer 38 and second timer 36 
located within the transmitter unit case in a conventional manner. 
The audio silence switch 56 labelled "AUDIO RESET" in FIG. 4 is coupled to 
the bell 68 on the receiver console in such a manner that by positioning 
the audio silence switch to the correct position the bell is prevented 
from ringing for that particular receiver/transmitter pair. It is used to 
silence the alarm to allow the remaining work areas to be monitored by the 
audible alarm circuitry while help is being sent to the individual work 
area transmitting the alarm. The bell silence mechanism is necessary so 
that the first alarm generated by a particular transmitter/receiver pair 
does not mask later alarms generated by other transmitter/receiver pairs. 
The alarm reset switch 58 on each receptacle and indicator panel is 
coupled to the strobe light and is used to reset the alarms and to turn 
off the strobe light and the red light on the display panel when the 
situation that necessitated the alarm has been cleared. 
In operation, the control console 40 is set up in the general area of a 
work station, for example, near an airplane under construction. The 
transmitter units 52 are mounted in the receptacles 54 within the receiver 
console during periods of nonuse. When a worker is to perform some task 
within one of the designated hazardous work areas he first reports to the 
control console and removes the transmitter unit assigned to the work area 
in which he is to be deployed, for example, in the illustrated embodiment 
if the worker is going to be working within the right hand wing of the 
aircraft he removes the transmitter unit that is in the receptacle 
associated with the right hand wing on the plan view outline of the 
airplane present on the control console panel. The worker then presses the 
alarm button 76 to insure that the alarm is working and activates both the 
visible and audible alarms on the control console as well as lighting the 
red light on the receptacle and indicator assembly associated with the 
transmitter unit that he has removed. If the alarm appears to be working 
satisfactorily, the worker silences the alarm, sets the reset button, and 
then presses the check-in button 72 on the transmitter unit to provide a 
green light at the receptacle and indicator assembly and to initialize the 
receiver first timer and transmitter second timer to begin operation. The 
worker then takes the transmitter unit with him to the designated work 
area. After a predetermined amount of time the transmitter unit second 
timer will run out and cause the transmitter unit buzzer to sound alerting 
the worker that he must check in. The worker then presses the check-in 
button and reinitializes both timers. Should the worker experience some 
difficulty while in the hazardous working area, for example a feeling of 
faintness or dizziness, he can press the alarm button on the transmitter 
unit thereby actuating the audible and visible alarms at the control 
console 40 and also causing a red light to be displayed on the receptacle 
and indicator assembly associated with his particular location on the 
console panel display. The monitoring personnel are then alerted that aid 
is required in his work station. Should the worker become faint and lose 
consciousness or in some other way become incapacitated so that he cannot 
press the alarm button or the check-in button, then upon expiration of the 
time period set into the first timer in the receiver the first timer will 
send a time out signal lighting the amber light on the receptacle and 
indicator assembly associated with his work location and again actuating 
the audible and visible alarms on the control console. This indicates to 
the monitoring personnel that for some reason a predetermined period of 
time has elapsed without a check-in by the worker and the monitoring 
personnel can dispatch aid to the worker's work station immediately to 
investigate the problem. 
For use in environments where the atmosphere may contain potentially 
explosive gases it is necessary the transmitter assembly be intrinsically 
safe, that is, that the amount of current generated within the transmitter 
should be of such a low magnitude that it would not set off an explosion 
due to sparking. Further it is desirable that the transmitter operating 
temperature remains rather low, both for personal safety of the user and 
for the prevention of explosive conditions. In order to insure proper 
operation of the transmitter during an entire working shift, it is 
preferable that the transmitter batteries have a life of approximately 16 
hours or two working shifts to provide a sizable safety margin should the 
batteries be out of their charging receptacle for a long period of time. 
It will be apparent to those of ordinary skill in the art that many 
changes can be made to the illustrated and described embodiments of the 
present invention and equivalent means substituted for certain components 
specifically named while remaining within the spirit and scope of the 
invention. Therefore, the scope of the invention should be determined 
solely by reference to the claims that follow.