Patent Publication Number: US-2002008625-A1

Title: Remote accountability system and method

Description:
[0001] This application claims the benefit of U.S. Provisional Application No. 60/186,074, filed Feb. 29, 2000, which is hereby fully incorporated by reference. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The invention relates generally to communication systems, and more particularly, to a method and system for communicating information between one or more remote portable accountability systems and one or more command systems.  
       BACKGROUND OF THE INVENTION  
       [0003] Many emergency situations such as, for example, fire fighting, require effective communications between the individuals responding to the emergency and a command or control center. However, present systems suffer from the disadvantage of providing only limited accountability information between the individuals responding to the emergency and the command and control center. Hence, there is a need for a robust accountability communication system that provides both the individuals responding to the emergency and the command and control center with information that may be vital to the safety of the individuals involved and the prosecution and resolution of the emergency.  
       SUMMARY OF THE INVENTION  
       [0004] The present invention provides a method and system having two-way messaging and a means for tracking personnel status by establishing wireless links between one or more mobile persons (portables) and a command post system. It is designed to improve the safety and efficiency of, for example, fire teams working in hazardous environments.  
       [0005] The system has one or more “portables” worn by one of more mobile workers and a command post system. Each portable is comprised of a small “black box” containing a radio transceiver, control circuitry, optional data communication ports, antenna and optional power source. The portable is preferably attached or otherwise affixed to a self-contained breathing apparatus (SCBA). These portable units communicate via radio frequency with a command post system. The command post system includes a base station radio with a display and a data communications port allowing connection to a Personal Computer for data downloading or real-time display of data.  
       [0006] The system preferably utilizes a polling radio network architecture providing robust two-way communications between the mobile portable units and the command post system. Improved radio link range and reliability are provided and the present invention seeks to maximize these features and to immediately alert users at both ends of the link in the event of an out-of-range condition. To maximize link range and reliability, the present invention employs robust link protocol that enhances acquisition, maintenance and re-acquisition of data in the event of momentary loss. This protocol provides for successful data transmission in situations where voice radio communications may be garbled. Critical messages such as evacuation alarms are continually re-sent until receipt is acknowledged. The command post system preferably supports up to 50 portable units.  
       [0007] Another preferable approach expand the system polling architecture to include a packet-mode when a mobile portable unit has been out of range for a predetermined period of time. This additional mode allows an out of range mobile portable unit to relay its information to another mobile portable unit, which is in range of the base station or command post. When a mobile portable unit has not received an inquiry from the base station or command post for a predetermined period of time, it will monitor the traffic present on its communication channel. This portable unit will then search for another mobile portable unit that is in range and forward its data to the base station or command post via the in-range portable unit. The base station or command post then communicates with the out of range mobile portable unit using this packet-mode relay approach until the out of range mobile portable unit can again communicate directly with the base station or command post.  
       [0008] System software and control circuits provide flexibility in choice of radio communication by having software programmable radio frequencies. This provides an easy migration to a different radio module (e.g., different frequency, data rate, and/or modulation technique) in the event of regulatory changes or if the system is to be used where radio spectrum changes would be required. The present invention preferably transmits signals in the ultra-high frequency (UHF) range and, most preferably, in the approximate range of 450 to 460 MHz.  
       [0009] Each portable unit has a unique digital address allowing for multiple portable units on a single radio network. The system of the present invention is particularly useful at fire scenes where multiple systems can be operating. This is possible because each system operates on its own frequency. Additional channels could be added to provide a “universal” channel if it is desirable to have firefighters from different departments operating from a single command post radio. The portable units can also be initialized via a personal key/tag or other device to carry personal identification and other information about the individual that will be automatically transmitted to the command post system.  
       [0010] Each portable is capable of receiving and transmitting a plurality of accountability information. For example, accountability information that can be transmitted from a portable includes video and audio information, external temperature, physiological characteristics, external pressure, SCBA status (i.e., air or time remaining), emergency signals, motion information, hazardous gases in the environment, and personal information.  
       [0011] Therefore, it is an advantage of the present invention to provide a SCBA-based portable unit for communicating accountability information to a command system.  
       [0012] It is another advantage of the present invention to provide an easily configurable portable unit that can be quickly programmed with personal information and unique identification information.  
       [0013] It is another advantage of the present invention to provide a robust communication protocol between one or more portables and a command system so as to maintain a constant communication link between the portables and the command system.  
       [0014] These and other advantages will be apparent from the below detailed description and drawing figures. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0015] In the accompanying drawings which are incorporated in and constitute a part of the specification, embodiments of the invention are illustrated, which, together with a general description of the invention given above, and the detailed description given below, serve to demonstrate the principles of this invention.  
     [0016]FIGS. 1A, 1B,  1 C, and  1 D are block diagrams illustrating various embodiments of the system of the present invention.  
     [0017]FIG. 2 is a block diagram illustrating certain components of a command post system of the present invention.  
     [0018]FIG. 3 is a block diagram illustrating certain components of a repeater unit of the present invention.  
     [0019]FIG. 4A is a block diagram illustrating certain components of a portable unit and sensor system of the present invention.  
     [0020]FIG. 4B is a diagram illustrating the general location of a portable unit and sensor system of the present invention in relation to the components of a Self-Contained Breathing Apparatus (SCBA).  
     [0021]FIG. 5 is a flowchart illustrating the logic flow of the present invention.  
     [0022]FIG. 6 is a diagram illustrating a portion of a display generated by the present invention.  
     [0023]FIG. 7 is a flowchart further illustrating the logic flow of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0024] Referring now the drawings and particularly to FIG. 1A, a first embodiment of the present invention embodied by system  100  is shown. The system  100  has at least one command post system  102  and at least one portable remote system  103 . In general, data is collected from sensor system(s)  108  by portable unit  106  and transmitted to command post system  102 . The nature of the data can be diverse, depending the specific application of the system. For example, in a chemical factory, it may be useful to transmit readings from a portable gas detector. If levels of certain gases reach an unsafe level, a supervisor can evacuate workers. In a fire fighting scenario, ambient environmental temperature and remaining air tank levels may be of more interest. In a combat setting, it might be desirable to transmit physiological data from soldiers. Other examples and descriptions of transmittable data and information will be described in more detail in connection with the description of FIG. 4A.  
     [0025] The portable remote system  103  is preferably worn by an individual such as, for example, a firefighter on a self-contained breathing apparatus (SCBA)  112 . Generally, there are N portable remote systems, where N is based on the number of individuals wearing the system. The portable remote system  103  preferably includes a portable unit  106  and, optionally, one or more sensor systems  108 . In FIG. 1A, the portable unit  106  communicates directly with command post system  102  via a radio-frequency (hereinafter RF) communication channel.  
     [0026] The command post system  102  is designed as a stand-alone system. However, it can be optionally connected to a computer system  110  such as, for example, a personal computer system or laptop or notebook computer system. The computer system  110  preferably includes one or more input/output devices such as, for example, displays, keyboards, touch pad, mouse, pointing stick, microphone, etc. The connection between command post system  102  and computer system  110  is preferably hardwired through serial, parallel, or RS- 232  interfaces. Alternatively, the connection can via RF or infrared signal in situations where a hardwired connection proves impractical or too difficult to achieve.  
     [0027] In operation, the command post system  102  and portable unit(s)  106  establish a master-slave relationship. More specifically, command post system  102  serves as a master and the portable units  106  serve as slaves. The command post system  102  communicates with the portable unit(s)  106  via a polling/retry communication architecture. More specifically, portable unit(s)  106  are required to respond to requests from the command post system  102 . The system is made robust by a message protocol that requires message acknowledgment from each portable unit  106 . If an acknowledgment is not received and understood by the command post system  102 , the message is resent several times. After several attempts, the command post system  102  alerts that the portable unit  106  is out of range or malfunctioning. Additionally, each portable unit  106  expects to be contacted by the command post system  102  at regular time intervals. If a particular portable unit  106  is not contacted after a preset time has elapsed, the wearer or user of the portable unit  106  is alerted that the command post system  102  is out of range. In this manner, both ends of the communications link are alerted if the link is interrupted. Each portable unit  106  also has the ability to transmit certain emergency signals or information without a request from the command post system  102 . These emergency signals or information are described in more detail in connection with FIGS. 4 and 5.  
     [0028] Where communication links are difficult to establish such as, for example, in large buildings and other massive structures, system  120  of FIG. 1B can be employed. System  120  is similar to system  100  of FIG. 1A, except that one or more repeater units  104  are employed to increase the range of communication between the portable unit(s)  106  and the command post system  102 . For example, in large buildings where concrete, metal, or other materials can cause the range of communication between the portable unit(s)  106  and command post system  102  to be shortened, a repeater unit  104  can be used to transmit and receive signals between the portable unit(s)  106  and command post system  102 . While only one repeater unit  104  is shown in FIG. 1B, multiple repeater units  104  can be employed depending on the desired or required range.  
     [0029] As an alternative to system  120  of FIG. 1B, system  130  of FIG. 1C has a repeater unit  104  associated with each portable unit  106 . In this embodiment, repeater unit  104  and portable unit  106  preferably communicate with each other via a short-link RF signal system so as to eliminate any physically corded connections between the two units. A short-link RF signal system is desirable because it minimizes or eliminates the physical restraints and dangers introduced by corded systems. In an alternate embodiment, the repeater unit  104  and portable unit  106  can be integrated into a single unit with hardwire communication connections therebetween.  
     [0030] As a further alternative to the above embodiments, a system  140  that utilizes a packet-mode communication architecture to further expand the range communications between a port unit  106  and a command post system  102  is provided. More specifically, this packet-mode communication architecture is particularly useful when the link between the portable unit  106  and base station or command post system  102  has been interrupted. In this regard, the out of range portable unit  106  monitors it communication channel to determine if it can “hear” any other portable units thereon and whether those units are in communication with the command post system  102 . If the out of range portable unit  106  find a portable unit  106 A, which is in communication with command post system  102 , it will communicate with that portable unit and use it as a relay to the command post system  102 .  
     [0031] In general, the location of portable unit  106  and sensor system  108  can be anywhere on a person&#39;s body. Nevertheless, portable unit  106  is preferably attached or otherwise affixed to the SCBA  112  worn on a person&#39;s body. Alternatively, portable unit  106  and sensor system  108  can be affixed near the face of a user as when located on a protective face mask. Other locations include near the shoulder, chest, or on the arm.  
     [0032] As will be described in more detail in connection with FIG. 4A, the location of sensor system  108  depends on the particular parameter(s) the sensor system  108  is sensing. Generally, each sensor of sensor system  108  can have its own location on a person&#39;s body, depending on the parameter being sensed. It is preferable that, to the extent possible, sensor system  108  is integrated into portable unit  106  to reduce the number discrete components required. In this regard, communication between individual sensors and the sensor system  108  is preferably hardwired, though it can also be RF where hardwiring is physically restrictive or impractical.  
     [0033] In the case of repeater unit  104  being a discrete component of system  130 , it is preferably worn a person&#39;s body at a location different from the portable unit  106  such as, for example, near a user&#39;s waist or hips. One important consideration in determining the locations for the repeater unit  104 , portable unit  106  and sensor system  108  is that they should minimally interfere with the range of physical motion required by the individual wearing the system. For example,, a firefighter may have the portable unit  106  incorporated into a protective face mask and the repeater unit  104  attached to the waist or hip.  
     [0034] Referring now to FIG. 2, a block diagram illustrating the command post system  102  is shown. More specifically, the command post system  102  is enclosed in a weatherproof housing and has a microprocessor  200 , memory  202 , modem  204 , transceiver  206 , antenna  208 , one or more input/output devices  210 , and an interface  212 , all in circuit communication as shown. As used herein, the term circuit communication means any form of electronic communication including hardwired, infrared, optical fibers, and/or electromagnetic.  
     [0035] The memory  202  preferably stores the programs or instructions responsible for directing the microprocessor&#39;s actions and all relevant data such as, for example, data collected from the portable unit(s)  106  and sensor system(s)  108 . Memory  202  is preferably large enough to store approximately  8  or more hours of data acquired from the portable unit(s)  106  and sensor system(s)  108 . Such data logging provides for comprehensive after-action reviews and documentation.  
     [0036] The modem  204  and transceiver  206 , along with antenna  208 , provide a two-way communication channel between the repeater unit(s)  104  and portable unit(s)  106 . Information or data is preferably transmitted between the command post system  102  and the repeater unit(s)  104  and portable unit(s)  106  via Quadrature Phase-Shift Keying (QPSK) modulation. In the alternative, other modulation techniques can be employed including digital bandpass modulations such, as, for example, Amplitude Shift Keying (ASK), Frequency Shift Keying (FSK), Phase Shift Keying (PSK), Differential PSK, M-ary modulation, Offset QPSK, and Quadrature Amplitude Modulation (QAM).  
     [0037] Input/output devices  210  preferably provide the command post system  102  with local input and output capability. For example, input and output devices  210  can include indicator lights, displays such as, for example, Liquid Crystal Displays (LCD&#39;s) that can generate graphic and textual messages, microphone(s), speaker(s), keyboard(s) and push-buttons.  
     [0038] Interface  212  is preferably an RS- 232  interface suitable for connection with the computer system  110 . Computer system  110  provides additional functionality and memory to the commander of the command post system  102 . For example, computer system  110  can display real-time video from one or more camera systems incorporated into sensor system(s)  108 . Additional functionality includes the networking of data to remote computers via the Internet or other network and the ability delegate command tasks to commanders that are networked in other locations. A power supply  214  is provided to power all the components of the command post  102 . The power supply  214  can be an internal battery and/or an external power supply such as, for example, an external AC or DC power source.  
     [0039] Referring now to FIG. 3, repeater unit  104  is shown in greater detail. The repeater unit  104  provides a high-power communications link between the relatively low-power portable unit  106  and the high-power command post system  102 . Portable unit  106  is low-power only in the sense that it produces a signal strength that has a limited range. Nevertheless, the range should be large enough so that the command post system  102  or repeater unit  104  can reliably pick-up the signal.  
     [0040] The repeater unit  104  preferably includes a microprocessor  300 , memory  302 , modem  304 , transceiver  306 , visual/audible indicators  314 , and antenna  308 . The modem  304  and transceiver  306 , along with antenna  308 , provide a two-way communication channel with the command post system  102  and portable unit  106 . The memory  302  is preferably flash upgradeable and stores the programs or instructions responsible for directing the microprocessor&#39;s actions and all relevant data such as, for example, data collected from the portable unit(s)  106  and sensor system(s)  108 . Memory  302  is preferably large enough to store approximately 8 or more hours of data acquired from the portable unit(s)  106 . Visual/audible indicators  314  preferably include lights and/or speakers that emit signals that assist in locating the repeater unit  104  such as, for example, when repeater unit  104  is a discrete component located somewhere in or near, for example, a building. An internal power supply  312  such as, for example, batteries, are provided to power the repeater unit  104 .  
     [0041] Referring now to FIG. 4A, portable unit  106  and sensor system(s)  108  are shown in more detail. As described earlier, the portable unit  106  receives and sends data and information either directly to the command post system  102  or through repeater unit  104 . Portable unit  106  preferably has a microprocessor or controller  400 , memory  402 , modem  404 , transceiver  406 , antenna  408 , a plurality of input/output devices  412 , an interface  416 , and power supply  420 . The portable unit  106  also includes an Analog-to-Digital (ADC) converter  418  that can be either integrated into microprocessor  400  or exist as a discrete component. ADC  418  allows for the input of analog data from sensor system(s)  108  for conversion into digital form. More generally, microprocessor  400  and other associated control circuitry are capable of accepting voice, data, and video signals and digitizing, buffering, and formatting such signals for transmission to the command post system  102  or repeater unit  104 . Microprocessor  400  also includes a clock for time-marking incident data in memory  402 . Incident data includes any status information sent to or received from command post  102 .  
     [0042] Modem  404  and transceiver  406 , along with antenna  408 , provide a two-way communication channel between repeater unit  106  and command post system  102 . Memory  402  is preferably flash upgradeable and stores the programs and instructions responsible for directing the microprocessor&#39;s actions and all relevant data such as, for example, data collected from portable unit(s)  106  and data received from the command post system  102 . Memory  202  is preferably large enough to store approximately 8 or more hours of data acquired from the portable unit(s)  106  and command post system  102 .  
     [0043] The input/output devices  412  preferably include status and message indicators that notify or alert the individual wearing the portable unit  106  of important status conditions and communications from the command post system  102 . Such devices include, for example, switches, push-buttons, speakers, indicator lights such as built-in LED arrays, integrated visual and audible indicators that use combinations of the preceding. Visual indicators include multicolor LEDs, LED arrays, alphanumeric displays, micro-displays, back-lit LCD displays, and others. The displays can include means of sensing ambient light levels and adjusting display brightness levels accordingly. For example, when used in sunlight, the brightness would be greater and, when used in darkness, the brightness would be reduced. Such displays are preferably located for optimum viewing by the user. The input/output devices  412  also include an electronic key interface and/or bar code reader for reading an electronic key or bar code  448 . The electronic key is preferably a non-volatile memory device that stores user information and identification data. Such devices include, for example, EEPROM&#39;s, smartcards and barcodes. The EEPROM and smartcard are electronic in nature and, store the data as series of binary numbers. These devices are user re-configurable and thus allow alterations of their contents. In the case of an EEPROM, it is preferably integral to a physical key device that is plugged into the portable unit to provide identification and personal information about the wearer. A smartcard-based system requires the user to insert the smartcard into an attached card reader, which would then read and transfer the user information to the portable unit. The smartcard can then be removed. A barcode based&#39;system preferably scans a barcode worn by the user and transfers the data to the portable unit. The type of code utilized is preferably one of several alpha-numeric barcode standards. For example, common alpha-numeric barcodes are Code  39 , Code  93 , Code  128  and LOGMARS, which is a U.S. Government standard. In this, regard, barcode technology can be employed to generate codes that are linked to data tables in microprocessor  400  or memory  402  that include information identifying the individual assigned to the portable unit  106 . The portable unit  106  also includes a Homing Signal generator  410 , which will be described in connection with FIG. 5.  
     [0044] The interface  416  of portable unit  106  provides a communication link  422  between the portable unit  106  and any sensor system(s)  108  that may be provided. The communication link  422  can be either hardwired or RF depending on the particular sensor system. Preferable sensor systems(s)  108  include one more of the following systems: motion detector(s)  424 , gas detector(s), Self Contained Breathing Apparatus (SCBA) status sensor  428 , pressure sensor(s), a BLUETOOTH communications module  432 , heads-up display  424 , camera  436 , microphone  438 , speaker  440 , temperature sensor  442 , physiological sensor(s)  444 , and a panic button  446 .  
     [0045] The motion detector  424  aids the command post system  102  and portable  106  to monitor whether the individual wearing the portable unit  106  has been motionless for a preset period of time, thereby indicating a possible critical condition. The gas detector(s)  426  aid the command post system  102  and portable  106  to monitor the presence and levels of hazardous environmental gases such as for example, methane or other explosive gases. The SCBA status sensor aids the command post system  102  and portable  106  to monitor, for example, the amount of breathing gas or time remaining in the SCBA. The pressure sensor  430  aids the command post system  102  and portable  106  to monitor the pressure in, for example, the SCBA or the external environment. The BLUETOOTH module  432  provides a short range RF communication channel either directly from the sensor system(s)  108  or from the portable unit  106  to other digital devices such as, for example, digital cell phones and personal digital assistants (PDA). The heads-up display  434  provides the individual wearing the sensor system  108  with an intelligent display that allows graphics and text to be displayed over a transparent window. The transparent window allows the wearer of the head-up display  434  to see messages thereon such as, for example, status information (e.g., temperature, remaining air, etc.) and alarms (e.g., evacuate now), while allowing the present environment to be seen. Information from the command post system  102  and/or portable unit  106  may also be displayed on the heads-up display  434 . Camera  436  provides a video signal as directed by the wearer of the sensor system  108  to command post system  102 . Camera  436  may be infrared, color, black and white, or any combination of the above. Microphone  438  and speaker  440  provide audible signals both to and from the wearer of the sensor system  108  to and from the command post system  102  and, optionally, to other team members who are wearing similar systems. Temperature sensor  442  monitors the environmental temperature and relays such information to the command post system  102 . Physiological sensor(s)  444  monitor the wearer&#39;s physiological parameters such as, for example, blood pressure, body temperature, heart rate, blood oxygen level, galvanic skin response, and brain activity. Information gathered from such physiological sensors is relayed to the command post system  102  for monitoring by a commander or medical professional. A panic button  446  is also provided so the wearer of the sensor system  108  can initiate a panic call to the command post system  102  and await instructions therefrom via the system&#39;s speaker  440 .  
     [0046] In addition to the above sensor system(s)  108 , the portable unit  106  can include an external audible system. The external audible system preferably includes a speech synthesis chip or system for connection via an external data port to speaker(s)  440 . When speaker(s)  440  include an external speaker, spoken status updates and/or alarms can be audibly broadcast over the speaker. For example, the remaining air levels in the SCBA tank, temperature levels, and evacuation alarms can all be broadcast using synthesized speech to the user. The portable unit  106  microprocessor  400  executes commands that provide for such functionality.  
     [0047] Illustrated in FIG. 4B is a diagram illustrating a the general location of portable unit  106  and sensor system  108  of the present invention in relation to a SCBA  112 . More specifically, a typical SCBA  112  has a portable breathing gas tank  448 , mask  454  and tubing  452  connecting the two components. Breathing gas tank  448  has a removable fitting  450  from which breathing gases can exit and to which tubing  452  can interface. Portable unit  106  and sensor system  108  are preferably affixed to SCBA  112  at or near fitting  450 . In this manner, pressure sensor  430  and SCBA status sensor  429  (shown in FIG. 4A) can be located on or near the breathing gas tank  448 . This arrangement facilitates convenient pressure measurement of breathing gas tank  448 . This arrangement also maintains the mechanical integrity of breathing gas tank  448  by not requiring any additional interfaces to monitor the status thereof such as, for example, pressure.  
     [0048] Referring now to FIG. 5, the operation of the present invention will be described in more detail. More specifically, FIG. 5 illustrates a flowchart  500  of the steps performed by the system of the present invention. In step  502 , independent of the command post system  102 , the portable unit(s)  106  can be automatically activated with pressurization of the SCBA or manually activated if an SCBA is not used. The logic next proceeds to step  504  where a series of sub-steps that initialize the system are performed. In particular, the command post system  102  transmits a request for any active portable unit  106  to respond. All active portables units  106  respond to the command post system  102  request with their unique address and other data if available such as, for example, user name and medical information. Portable units  106  use synthesized radio transceivers that allow the portable unit  106  particular radio frequency to be programmed via software in the memory of each portable unit  106 .  
     [0049] Active portable units  106  can be manually accepted or rejected by the commander using the command post system  102 . As the portable units  106  respond, the command post system  102  builds a connectivity list of all active portable units  106  accepted by the incident commander. Because each portable unit  106  has a unique address, more than one accountability system (e.g., system  100 ,  120 , or  130 ) of the present invention can operate in the same area. This is possible because the RF of each portable unit  106  is programmable via software and can be easily changed from command post system  102 . Hence, command post system  102  has ability to accept or reject particular portable units  106  in defining it command responsibilities.  
     [0050] Once all of the portable units  106  have been logged into the command post system  102 , operation progresses to step  506  where the system enters a monitoring/command mode. In this mode, the command post system  102  transmits queries to portable units  106  requesting status or data updates. Upon receipt of a query, a portable unit  106  transmits a status update to the command post system  102 . This data is preferably related to the above described sensor system(s)  108 . In step  508 , microprocessor  400  in the portable unit  106 , or alternatively, microprocessor  200  in the command post system  102 , checks the data against thresholds to determine if any alarms should be generated. In step  510 , if data from a portable unit  106  is above or below preset thresholds, this condition is flagged as an alarm condition at the command post system  102  with both an audible and a visual alert. Upon receiving an alarm, the commander can activate the portable unit  106  homing signal function so that a rescue team can enter the building and find the affected user.  
     [0051] Under certain other conditions, a commander may want to evacuate an individual, a team, or everyone in an emergency situation. This condition is represented in step  512 . For example, if a firefighter&#39;s air is low as indicated by his SCBA status sensor  428 , the commander may choose to evacuate the individual. If a building&#39;s roof is in danger of imminent collapse, a commander may choose to issue a general evacuation call to all firefighters. Using the command post system  102 , the commander may direct an “evacuate now” message to the designated individual or group. The message can take the form of an audio signal on the user&#39;s speaker  440 , a message on the user&#39;s heads-up display, a visual signal such as a flashing red light on the portable unit  106 , or combinations of the above.  
     [0052] Users can notify the command post system  102  that they&#39;ve safely evacuated a building with a Respond/Clear button on the portable unit  106 , which would be read in received in step  506 . This allows a commander to keep track of those individuals who have received the evacuation alert and have safely exited the area and those that have not exited. Armed with this knowledge, the commander can activate the homing signal of any remaining users and mount a search effort for those individuals.  
     [0053] As previously described, the portable units  106  can transmit certain alarm messages without a query from the command post system  102 . These messages include a “distress alarm,” which can be manually activated in the event of emergency. Additional alarm messages include a Personal Alert Safety System (PASS) alarm that is automatically generated by the portable unit  106  if the sensor system  108  motion detector  424  does not sense motion for a preset period of time.  
     [0054] In the event that a Not Acknowledge (NAK) signal or no signal is received in response to a query to a portable unit  106 , command post system  102  will re-send the query a specified number of times. After the number of tries (the number is software configurable) has expired, the command post system  102  generates an “Out of Range” alert for the portable unit(s)  106  not responding to the query. Additionally, a portable unit  106  that does not receive a query from the command post system  102  for specified period of time will report via an audible and/or visual “Out of Range” alert to the user of the portable unit  106 .  
     [0055] As described above, portable units  106  send status updates upon receipt of a query from the command post system  102 . The type of status updates or queries preferably depend on the number and type of peripherals or sensor system(s)  108  attached to the portable unit  106 . For example, if a self-contained breathing apparatus (SCBA) status sensor and a temperature sensor are connected, portable unit  106  transmits the latest air pressure in the tank of the SCBA and the latest environmental temperature. In this regard, the command post system  102  polls each active portable unit  106  on a regular basis to receive status or data updates.  
     [0056] In order to increase the robustness of the system, the command post system  102  can receive emergency messages from portable units  106  that are not logged onto the system&#39;s original log table. This ensures that a user&#39;s emergency signal can be received by any and all command post systems  102  that are in the vicinity or locality. Also in this regard, the command post system  102  can send general messages such as “evacuate all” to all portable units  106 , including units not logged into the system.  
     [0057] Personnel location is determined in the Monitoring/Command mode via a homing function. More specifically, each portable unit  106  includes electronics to help a rescue team locate the user. These electronics are primarily embodied in the homing signal generator  410 . A homing beacon or signal in the portable unit  106  is activated either automatically or remotely from the command post system  102 . Upon receipt of a distress alarm from a portable unit  106 , a commander can activate the portable unit  106  homing signal generator  410 . A rescue team using a locate device having a directional antenna, Radio Signal Strength Indicator (RSSI) and readout could locate the individual by moving toward the portable unit  106  homing signal.  
     [0058] The system of the present invention may either alternatively, or additionally, incorporate other technologies that assist in locating a person in distress. For example, the portable unit  106  of the present invention can incorporate an altimeter and a “dead reckoning” system. Such a system creates a directional trail (i.e., distance traveled, direction traveled, height (e.g., which floor) or number and type of steps taken), that a rescue team could follow to locate and extract an individual. The system may further incorporate a Global Positioning System (GPS) in the portable unit  106 , which is particularly useful for locating individuals in outdoor situations.  
     [0059] Still referring to FIG. 5, operation of the present invention continuously loops in the monitoring/command mode of operation until an exit is desired, as determined in step  514 . For example, the system exits the monitor/command mode when it is desired to shut-down the system. Otherwise, the system loops back to step  506 .  
     [0060] Referring now to FIG. 6, a portion  600  of a display that can be generated by the command post system  102  or computer system  110  is shown. The portion  600  includes at least one portable unit information area  602  that displays status information from a portable unit  106  that is logged into the command post system  106 . The area  602  includes a remote identification number  604 , key identification  606 , and sensor system status information such as, for example, tank pressure  608  and suit temperature  610 . The area  602  also includes a “Homing” status indication  612 , PASS alarm status indication  614 , and elapsed time meter  622 . The “Homing” status  612  indicates if the portable unit  106  homing signal function has been activated. Similarly, the PASS alarm status  614  indicates if the PASS alarm has been activated. In general, any information provided by any sensor system  108  in communication with portable unit  106  can be displayed in area  602  including, for example, video from camera  436  and physiological data from physiological sensor(s)  444 .  
     [0061] Display portion  600  also allows a commander to see the list of portable units  106  that are logged onto the command post system  102 , individual or team status information, elapsed time  622 , and out of range alerts for any portable unit (when appropriate.) Alarm conditions are flagged visually and audibly. For example, an alarm condition can be represented as an audible signal and a text message that is colored red and flashing on the display. Normal conditions are preferably displayed in green color. Other color combinations are possible, but the color combination of red and green are the most universally understood to mean alarm and condition clear, respectively.  
     [0062] As described earlier, a commander can transmit evacuation messages to individuals, teams or, all portable units  106 . In this regard, display portion  600  includes visible instructions on how these functions are initiated. For example, display portion  600  includes an “Evacuate All” instruction  616  that directs depression of an “F 1 ” key or button for initiation of the function. Similarly, display portion  600  includes “Evacuate Individual” and “Home Individual” instructions  618  and  620 , respectively, that direct depression of the “F 2 ” and “F 3 ” keys or buttons, respectively, to initiate such functions. Individuals or portable units  106  that have responded to the evacuation signal and have cleared the area can acknowledge so and their status will be reported on the command post system  102  and/or computer system  110 . Messages in this regard are displayed in the appropriate portable unit information area  602 .  
     [0063] While the present invention has been illustrated by the description of embodiments thereof, and while the embodiments have been described in considerable detail, it is not the intention of the applicant to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, the constituents of the command post system, portable unit, and sensor system can be varied and still obtain the functionality and structure described herein. Additionally, the system communication and control approach can be varied while still maintaining a robust communications architecture. Moreover, the location of various components of the present invention can be modified without affecting their function and purpose. Therefore, the invention, in its broader aspects, is not limited to the specific details, the representative apparatus, and illustrative examples shown and described. Accordingly, departures can be made from such details without departing from the spirit or scope of the applicant&#39;s general inventive concept.