Hazard warning system method and apparatus

Abstract

In one aspect the invention provides a hazard warning system including a personal warning apparatus to be carried by a person in proximity to at least one hazard. The personal warning apparatus includes a sound pulse receiver capable of detecting the amplitude of received sound pulses and the duration of received sound pulses, and an alarm indicator configured to alert the person carrying the warning apparatus of the presence of a hazard. Also provided is a controller configured to receive at least one signal from the sound pulse receiver representing a coded sequence of received sound pulses with amplitudes above a threshold amplitude and with a time delay between at least two sound pulses. The controller is programmed to determine if a received coded sound pulse sequence is valid and to activate the alarm indicator on the receipt of a valid coded sequence of sound pulses.

Description

[0001] Hazard warning system method and apparatus Field of the Invention

[0002] This invention relates to hazard warning systems, methods and apparatus. In various implementations the invention may be used to mitigate the occurrence of false positive detection of hazards.

[0003] Background of the Invention

[0004] Many environments contain hazards which the people present need to be aware of. For example, manufacturing environments can contain operating machinery which is dangerous to nearby workers and may also contain mobile machinery or vehicles which present collision hazards. Construction sites can incorporate areas which workers are to be excluded from and can also again contain mobile machinery which forms a collision hazard. Various environments can therefore contain static hazards in addition to mobile hazards formed by moving machinery or vehicles. Attempts have been made to develop hazard warning systems which can improve the situation awareness of people in an environment, and also the awareness of drivers or operators of machines and vehicles. Vehicle operators in particular need to be aware of the location and direction of travel of nearby workers to prevent collisions and injury. Similarly, workers moving in the operational area of static or moving machinery need to be aware of the presence of this equipment, and preferably when applicable the direction of travel of such hazards.

[0005] Existing prior art hazard warning systems have been developed for these circumstances which operate using range finding technologies. These systems normally rely on transmitters and receivers mounted to hazards as well as worn by the occupants of a region. It is known for these prior art systems to transmit and receive optical, radiofrequency or other bands of electromagnetic (EM) radiation in the determination of distances between people and hazards. These electromagnetic based systems operate at high speed based on measuring round-trip travel time of EM transmissions reflected from people and hazards in a region, with light speed transmissions allowing for multiple measurements in short time spans.

[0006] However these electromagnetic based systems may not necessarily perform effectively, accurately or reliably in certain environments.

[0007] These systems can suffer from multipath errors that occur when a signal is reflected from a target an angle which causes it to return to a transmitter by aconvoluted path of additional reflections. These additional reflections increase the propagation time of the signal and result in an erroneous distance calculation which is greater than it should be.

[0008] Other environments can experience high levels of electromagnetic noise, such as that generated by radiofrequency sources or high-power alternating current utilised by machinery. In some situations this noise can span the band of frequencies used by the electromagnetic transmitters of the hazard warning system, making it difficult to discern the valid returned reflections from transmitters used by the system.

[0009] Environments which contain metal structures or objects also present a challenge to electromagnetic based hazard warning systems. Metal objects present in proximity to such systems can absorb and attenuate their transmissions, preventing signal returns of appropriate power from being received and assessed to determine range information.

[0010] Hazard warning systems have also been developed which do not rely on electromagnetic radiation and in particular utilise high-frequency sound or sonar transmissions.

[0011] Although sound transmissions travel much slower than the electromagnetic radiation, they do not suffer from multipath reflection errors. Multiple reflections substantially attenuate the power of the sound signal to a point where it can be easily discerned from that of a direct path reflection. Metal objects and electromagnetic noise emissions also have no appreciable impact on systems using sound transmissions.

[0012] Again sonar based hazard warning systems can be implemented by mounting transmitters or sounders on hazards, with sonar receivers being carried or worn by people in a hazardous environment. The hazard mounted sounders can also incorporate a radio transmitter and receiver as can the devices carried by people. The start of the transmission of a sonar pulse from the hazard can also be synchronised with a corresponding radiofrequency (RF) transmission from the same hazard. This RF transmission can incorporate hazard or sounder identification information in addition to marking the start of the transmission time of a sonar pulse from the hazard. A receiving user device will start a timing process on receipt of the sounder's initial RF transmission with a propagation time been recorded on receipt of the corresponding sonar pulse from the hazard.However sonar based warning systems experience complications in their operation due to the relatively low speed of sound in air.

[0013] Some existing sonar based warning systems seek to operate efficiently by focusing on a finite or maximum operational range - any person outside of this maximum radius from a hazard are deemed not to be of concern. The attenuation of the power of a sonar pulse travelling through air also enables this approach with longer ranges resulting in received low power sonar pulses being ignored.

[0014] However in some circumstances this approach can result in false positive triggering of the hazard warning system. For example some environments can contain sources of high ambient noise emitting at the same frequency as the sonar pulse frequency or having harmonic frequencies which are the same frequency as the sonar pulse frequency. The power of the received audio noise may be above the cut-off threshold required by the hazard system for identifying valid nearby sonar pulses, potentially resulting in hazard warnings being issued when no hazard is present. Furthermore in some circumstances a sonar pulse travelling a distance greater than the maximum operational range of the system may not necessarily experience significant attenuation of its power or amplitude during transmission. These high-power long-range pulses may be confused by a receiver with pulses emanating from a hazard sounder within the maximum operational range of the system. In these arrangements the system cannot process travel times greater than its maximum operational range, so the received long-range pulse will be determined to have a travel time equal to the remainder of the actual travel time when integer multiples of the maximum propagation delay are subtracted. This characteristic of such systems can therefore result in the false positive detection of hazards in close proximity which are not present.

[0015] It would be of advantage to have improvements in the field of hazard warning systems which addressed any of the above limitations of the prior art or at least provided the public with an alternative choice. In particular it would be an advantage to have improvements in the field of sonar based hazard warning systems which reduce the occurrence of false positive hazard warnings.

[0016] Disclosure of the Invention

[0017] According to one aspect of the present invention there is provided

[0018] a hazard mounted warning apparatus configured for engagement with a hazard, the apparatus including

[0019] at least one sound emitter, anda controller configured to activate the sound emitter to emit a coded sequence of sound pulses and time delays between sound pulses, each of the sound pulses and time delays having the same duration,

[0020] the coded sequence being made up of a plurality of pulses and at least one time delay.

[0021] According to a further aspect of the invention there is provided a personal warning apparatus to be carried by a person in proximity to at least one hazard, the apparatus including

[0022] a sound pulse receiver capable of detecting the amplitude of received sound pulses and the duration of received sound pulses,

[0023] an alarm indicator configured to alert the person carrying the warning apparatus of the presence of a hazard,

[0024] a controller configured to receive at least one signal from the sound pulse receiver representing a coded sequence of received sound pulses with amplitudes above a threshold amplitude and with a time delay between at least two sound pulses, the controller being programmed to determine if a received coded sound pulse sequence is valid and to activate the alarm indicator on the receipt of a coded sequence of sound pulses determined to be valid.

[0025] Preferably the controller is programmed to determine if a received coded sound pulse sequence is valid by:

[0026] i. identifying sound pulses in the sequence that exceed a threshold amplitude, and

[0027] ii. determining that the coded sound pulse sequence is valid if the starting or ending half of the coded sequence includes an identified sound pulse and a time delay and the remaining half of the sequence includes two consecutive identified sound pulses.

[0028] Preferably the coded sequence may incorporate a time delay between at least two sound pulses

[0029] Preferably the coded sequence is non-symmetrical about the midpoint of the sequence.

[0030] According to another aspect of the present invention there is provided

[0031] a hazard mounted warning apparatus substantially as described above wherein the starting or ending half of the coded sequence includes a pulse and a time delay, and the remaining half of the sequence includes two consecutive sound pulses.Preferably the coded sequence has a total duration equal to four times the duration of a sound pulse or a time delay.

[0032] Preferably the first half of the coded sequence includes a sound pulse followed by a time delay and the second half of the sequence including two consecutive sound pulses.

[0033] Alternatively the first half of the sequence includes two consecutive sound pulses, and the second half of the sequence includes a time delay followed by a sound pulse.

[0034] According to another aspect of the invention there is provided a hazard warning system which includes

[0035] at least one hazard mounted warning apparatus substantially as described above, and

[0036] a plurality of personal warning apparatus each to be carried by a person as substantially described above.

[0037] According to a further aspect of the invention there is provided a method of determining the validity of sound pulse sequences emitted by a hazard mounted warning apparatus characterised by the steps of:

[0038] i. identifying sound pulses in the sequence which exceed a threshold amplitude, and

[0039] ii. determining that the sound pulse sequence is valid if the starting or ending half of the coded sequence includes an identified sound pulse and a time delay, and the other half of the sequence includes two consecutive identified sound pulses.

[0040] According to yet another aspect of the invention there is provided a set of computer executable instructions stored on a computer readable medium arranged for execution by the controller of a warning apparatus, the instructions determining the validity of a received coded sequence of sound pulses with time delays between sound pulses by executing the steps of,

[0041] i. identifying sounds pulses in the sequence which exceed a threshold amplitude, and

[0042] ii. determining that the sound pulse sequence is valid if the starting or ending half of the coded sequence includes an identified sound pulse and a time delay, and the other half of the sequence includes two consecutive identified sound pulses.According to a further aspect of the invention there is provided a set of computer executable instructions stored on a computer readable medium arranged for execution by the controller of a hazard mounted warning apparatus, the instructions executing the step of operating a sound emitter to emit a coded sequence of sound pulses and time delays between sound pulses, each of the sound pulses and time delays having the same duration, where the starting or ending half of the coded sequence includes a pulse and a time delay, and the other half of the sequence include two consecutive sound pulses.

[0043] The present invention relates to the field of hazard warning systems. The invention spans a number of aspects related to the implementation of technology used to provide the required hazard warnings. In various aspects the invention provides a hazard mounted warning apparatus configured for engagement with a hazard in addition to a personal warning apparatus carried by person likely to encounter a hazard. The invention also provides a hazard warning system composed of various apparatuses carried by people or mounted to hazards, in addition to methods of operating such apparatus. Also provided are sets of computer executable instructions run by controllers integrated into such apparatus.

[0044] Reference in general throughout this specification will predominantly be made to the invention being a hazard warning system and / or a hazard warning apparatus mounted to a hazard or carried by a person. Those skilled in the art will however appreciate that the invention also spans the additional aspects referenced above and reference simply to systems or apparatus throughout this specification should in no way be seen as limiting.

[0045] The invention includes or incorporates a hazard mounted warning apparatus in various embodiments. This apparatus is mounted or engaged with a hazard and includes at least one sound emitter and a controller which operates to activate and deactivate the sound emitter.

[0046] The controller of a hazard mounted warning apparatus may be implemented by any appropriate form of programmable logic device or processor. Those skilled in the art will appreciate that a wide range of technologies may be used to implement such a controller - such as for programmable gate arrays, application specific integrated circuits and / or general-purpose microprocessors. The processor or controller provided can be loaded with computer executable instructions from a computer readable medium, with the execution of these instructions again facilitating a method of operating the hazard warning system.In preferred embodiments the sound emitter may be provided by various forms of well-known acoustic transducers operable to generate sound waves on demand. The sound emitter employed by the invention may be arranged to emit pulses of sound at selectively frequencies or within selected frequency bands and with a controlled amplitude or power. Those skilled in the art will appreciate that various forms of acoustic transducers well known in the art may be used as sound emitters in accordance with the invention.

[0047] In various embodiments the sound emitter used by the invention may be arranged or operated to emit sound in the ultrasonic range above 20 kHz. In further preferred embodiments such an emitter may be configured or operated to emit sound at approximately 32 kHz. In yet further embodiments such an emitter may be configured or operated to emit sound at approximately 39-41 kHz. Those skilled in the art will appreciate that the invention may be used to emit high-frequency sound at a range of frequencies and may utilise a vibrating diaphragm or any other appropriate form of sound transducer in the implementation of the invention.

[0048] In preferred embodiments a hazard mounted warning apparatus may include a radiofrequency transmitter, preferably connected to and operated by its controller. In such embodiments this RF transmitter may be operated to transmit a timing signal at the same time as the sound emitter starts to emit a coded sound pulse sequence. The combination of sound and radiofrequency transmissions can then be used by a remote receiving apparatus to measure the transit time of sound from the related hazard.

[0049] In additional aspects the invention provides at least one personal warning apparatus carried by a person. This apparatus incorporates a sound pulse receiver capable of detecting the amplitude of received sound pulses and the duration of these received sound pulses. Those skilled in the art will appreciate that any appropriate microphone system or equivalent acoustic transducer may be used to implement such a sound pulse receiver. In various preferred embodiments the sound pulse receiver may provide an output electrical signal representative of both the amplitude and duration of any detected or received sound pulse.

[0050] Again a personal warning apparatus includes a controller. This controller is preferably arranged receive at least one signal from the sound pulse receiver which is representative of the sound pulses it receives. This controller can again be implemented by any appropriate form of programmable logic device or processor. Those skilled in the art will appreciate that a wide range of technologies may be used to implement such a controller, such as for programmable gate arrays, application specific integrated circuits and / or general-purpose microprocessors.Furthermore the processor or controller provided can be loaded with computer executable instructions from a computer readable medium, with the execution of the instructions facilitating the method of operating the hazard warning system to be provided.

[0051] A personal warning apparatus incorporates an alarm indicator configured to alert the person carrying the warning apparatus of the presence of a hazard. This alarm indicator may take a variety of forms in various embodiments and can, for example, include an audio warning speaker and / or warning lights. In additional implementations the alarm indicator may also communicate with remote components or systems which also facilitate the provision of warnings of hazards to other users of the invention, not just the person carrying the related warning apparatus.

[0052] Reference in general is made throughout this specification to the various components of a hazard mounted warning system or a personal warning system being deployed together, preferably at the same location or within a common housing. However in various embodiments well know communications and information technology may facilitate implementation of a distributed architecture with - for example - cloud computing technology used to implement various processors or controllers. Furthermore an alarm indicator provided by a personal warning system may also include remote components used - for example - to alert operators of various machinery based hazards to the proximity of a person and could also include components arranged to disable the operation of such hazards. In preferred embodiments a personal warning apparatus may include a radiofrequency receiver, preferably connected to and able to supply signals to its controller. In such embodiments this RF receiver may be used to receive a timing signal transmitted from a remote hazard at the same time as a coded sound pulse sequence is emitted from this hazard. The combination of sound and radiofrequency transmissions can then be used by the processor of the personal warning apparatus to measure the transit time of sound from the related hazard.

[0053] The controller of a hazard mounted warning apparatus is configured to activate the sound emitter to emit a coded sequence of sound pulses and at least one time delay between sound pulses. This combination of sound pulses and a time delay or delays can have the same duration, in effect allowing the transmission of a binary data word with a sound pulse representing 'one' and a time delay represent 'zero'. In a preferred embodiment the coded sequence of sound pulses and at least one time delay may have a total duration equal to four times the duration of a soundpulse or time delay. Preferably as each sound pulse or time delay is of the same constant duration this coded sequence will therefore be composed of combination of four parts or elements.

[0054] In a preferred embodiment the duration of a sound pulse or time delay may be set to the expected travel time of a sound pulse emitted at a maximum operational range of a warning system. In these embodiments the system may be optimised so as to provide effective warnings to users without significant impacts on the time required to transmit an entire coded sequence of sound pulses and a time delay or delays. This maximum operational range can be represented by a sound travel time for the distance within which hazards are to be identified and warned of.

[0055] In preferred embodiments the coded sequence may include a time delay between at least two pulses. This characteristic of a coded sequence allows the presence of a time delay deliberately inserted into the sequence to be detected - as opposed to normal circumstances where the absence of a transmitted sound pulse is same as a continuous series of time delays.

[0056] In preferred embodiments the coded sequence is not symmetrical about the midpoint of the sequence. This characteristic of the coded sequence used allows for the detection and invalidation of received sequences which have experienced a greater travel time than pulses which originate from inside a maximum operational range of a personal warning apparatus. This extra delay will result in each consecutively transmitted part of the sequence being received later than normally expected, therefore re-ordering the sequence actually received by a user carrying the warning apparatus. The asymmetrical character of coded sequence therefore ensures that these long delayed sequences are not the same as that expected of a sequence emitted inside the maximum operational radius of the personal warning apparatus.

[0057] Those skilled in the art will appreciate that references to a coded sequence being symmetrical or asymmetrical refer to whether a sequence is a mirror image of itself centred on the mid or halfway point through the sequence. This characteristic of the sequence can readily be determined for those with an even number of members of sound pulses and time delays, while for odd-numbered sequences the central element would be disregarded.

[0058] In preferred embodiments the starting or ending half of a coded sequence may include a pulse in a time delay, and the remaining half of the sequence may include two consecutive sound pulses. This arrangement of a coded sequence provides asymmetry, with either the start or the end of the sequence including pulses and atime delay being discernible from the remainder of the sequence including two consecutive sound pulses. For example, in some embodiments the first half of a sequence may include a sound pulse followed by a time delay and the second half of the sequence may include two consecutive sound pulses. Alternatively in other arrangements the first half of a sequence may include two consecutive sound pulses and the second half of the sequence may include a time delay followed by a sound pulse.

[0059] As indicated above the present invention also encompasses a method of determining the validity of sound pulse sequences as well as computer executable instructions to facilitate this method.

[0060] Preferably this validation method may operate to identify sound pulses in a received coded sequence which exceed a threshold amplitude. This threshold amplitude may be set to an expected amplitude of a sound pulse emitted by a hazard mounted warning apparatus inside or at a predetermined maximum operational range of a warning system. This approach can therefore eliminate from consideration low amplitude sound signals which have been attenuated to travelling distances greater than this maximal operational range. Any received sound signal below this threshold will therefore be treated as effectively as a time delay.

[0061] A received coded sequence of such identified sound pulses and a time delay or delays can then be processed by a subsequent step to determine if it is valid. In various embodiments the coded sequence will need to match a predetermined valid coded sequence if it is to be determined to be valid. If for example a received coded sequence has travelled a distance greater than the maximum operational range of the warning system each of the sub-elements of the sequence will be time shifted by being received later than expected, thereby changing the order of the components of a fixed length sequence as received by a personal warning apparatus. This approach therefore allows for the invalidation of coded sequences which incorporate sound pulses above a threshold amplitude if these pulses have been transmitted from outside of the maximum operational range of the system. In embodiments where the start of a transmission of coded sequence of sound pulses is accompanied by an R.F timing signal this approach can prevent confusion between sound sequences transmitted concurrently from hazards both inside and outside the maximum operational range of a system. In particular, coded sound sequences from inside this range will be received and processed in the correct order in which they are transmitted. Conversely the additional transit time required of sound transmitted from outside of this maximum range can result in the wrong,later parts of a coded sequence being received first as dictated by the use of the RF timing signal.

[0062] Brief description of the drawings

[0063] Additional and further aspects of the present invention will be apparent to the reader from the following description of embodiments, given by way of example only, with reference to the accompanying drawings in which:

[0064] • Figure 1 provides an exemplary layout sketch of an arrangement of a personal warning apparatus, hazard mounted warning apparatuses and a static ambient source of sound noise,

[0065] • Figure 2 provides a table representing sound pulse signals as transmitted by hazard mounted warning apparatus and as received by the personal warning apparatus of figure 1 in accordance with the prior art,

[0066] • Figure 3 provides tables representing the timing of sound pulse signals as transmitted and received by the hazard mounted warning apparatus and personal warning apparatus of figure 1 when implemented in accordance with one embodiment of the invention.

[0067] Further aspects of the invention will become apparent from the following description of the invention which is given by way of example only of particular embodiments.

[0068] Best modes for carrying out the invention

[0069] Figure 1 provides an exemplary layout sketch of an arrangement of a personal warning apparatus P, hazard mounted warning apparatuses Hl, H2 and a static ambient source of sound noise Nl.

[0070] In the arrangement shown the personal warning apparatus P is worn by a person to be warned. This apparatus is configured to operate with a maximum operational range of approximately 17 meters, equating to a 50ms transit time for sound in air in most circumstances.

[0071] An ambient noise source Nl is located inside this maximum operational radius at 25ms travel time from personal warning apparatus P. This noise source emits a constant high amplitude sound containing the frequencies which the personal warning apparatus is configured to detect.

[0072] The nearby hazard has a hazard mounted warning apparatus Hl installed with both located 35ms travel time from the person to be warned. A remote hazard has ahazard mounted warning apparatus H2 installed with both located 115ms travel time from the person to be warned.

[0073] Figure 2 presents the following table also reproduced below representing sound pulse signals as received by the personal warning apparatus P of figure 1 when implemented in accordance with the prior art.

[0074] Sounds pulse receipt times at P

[0075]

[0076] With this prior art configuration both Hl and H2 emit a sound pulse at time T=0. Noise source N1 constantly emits sound and is equivalent to a constant string of sound pulses above a threshold amplitude required to be considered valid.

[0077] The prior art personal warning apparatus P receives the sound pulse from Hl at time = 35ms and correctly determines the distance to the Hl hazard as it is inside the maximum operational range of the system.

[0078] Personal warning apparatus P receives the sound pulse transmitted at time T = 0 by remote hazard H2 at time T = 115ms. In the circumstances illustrated this sound pulse is above a threshold amplitude required to be considered valid but is transmitted from outside the maximum operational range of the system. P misinterprets these circumstances by operating on the basis of the signal from H2 being transmitted at time T = 100 and calculates it as having a transit time of 15ms. This 15ms transit time equates to a distance from P which triggers the generation of a false positive warning.

[0079] Personal warning apparatus P receives the sound noise transmitted by noise source N1 at all times. P therefore receives what is effectively a sound pulse signal above a required threshold amplitude at time T = 0. Personal warning apparatus P therefore triggers the generation of a false positive warning for a hazard assumed to be at the same location as P.

[0080] Figure 3 provides tables representing the timing of sound pulse signals as transmitted and received by the hazard mounted warning apparatus Hl, H2 andpersonal warning apparatus P of figure 1 when implemented in accordance with one embodiment of the invention.

[0081] In particular figure 3 presents the following table also reproduced below representing the times at which sound pulse signals are transmitted by noise source N1 and hazard mounted warning apparatus Hl, H2.

[0082] Sounds pulse transmission times from Hl, H2, N1

[0083]

[0084] As illustrated by this table noise source N1 again constantly emits sound and is equivalent to a constant string of sound pulses above a threshold amplitude required to be considered valid.

[0085] At time T=0 both Hl and H2 being to transmit the same valid coded sequence of sound pulses and a time delay. In the embodiment of the invention illustrated Hl and H2 operate continuously to repeat these transmissions.

[0086] Figure 3 also presents the following table reproduced below representing the times at which sound pulse signals are received at personal warning apparatus P.

[0087] Sounds pulse receipt times at P

[0088]

[0089] Personal warning apparatus P receives the valid coded sound pulse sequence '1011' from Hl transmitting at 35ms distance. As the correct coded sequence is received this distance for Hl is determined by P to be valid.

[0090] Personal warning apparatus P receives the invalid coded sound pulse sequence '1110' from H2 transmitting at 115ms distance. This is due to H2 continuously transmitting the same originally valid coded sequence, but due to the additional 100ms travel time required P receives this coded sequence as starting with the second half of the coded sequence followed by the first half. These transmissions are deemed to be invalid by personal warning apparatus P.

[0091] Personal warning apparatus P receives the invalid coded sound pulse sequence '1111' from noise source N1 transmitting at 25ms distance. As the correct coded sequence '1011' is not received the noise source is not determined to be a hazard at the same location as personal warning apparatus P.

[0092] It is to be understood that the present invention is not limited to the embodiments described herein and further and additional embodiments within the spirit and scope of the invention will be apparent to the skilled reader from the examples illustrated with reference to the drawings. In particular, the invention may reside in any combination of features described herein or may reside in alternative embodiments or combinations of these features with known equivalents to given features. Modifications and variations of the example embodiments of the invention discussed above will be apparent to those skilled in the art and may be made without departure of the scope of the invention as defined in the appended claims.

Claims

What we claim is:

1. A personal warning apparatus to be carried by a person in proximity to at least one hazard, the apparatus includinga sound pulse receiver capable of detecting the amplitude of received sound pulses and the duration of received sound pulses,an alarm indicator configured to alert the person carrying the warning apparatus of the presence of a hazard,a controller configured to receive at least one signal from the sound pulse receiver representing a coded sequence of received sound pulses with amplitudes above a threshold amplitude and with a time delay between at least two sound pulses,the controller being programmed to determine if a received coded sound pulse sequence is valid and to activate the alarm indicator on the receipt of a coded sequence of sound pulses determined to be valid.

2. The personal warning apparatus of claim 1 wherein the controller is programmed to determine if a received coded sound pulse sequence is valid by:i. identifying sounds pulses in the sequence that exceed a threshold amplitude, andii. determining that the coded sound pulse sequence is valid if the starting or ending half of the coded sequence includes an identified sound pulse and a time delay, and the remaining half of the sequence including two consecutive identified sound pulses.

3. The personal warning apparatus of claim 1 which includes a radiofrequency receiver.

4. The personal warning apparatus of claim 3 wherein the radiofrequency receiver is connected to and able to supply the controller a timing signal transmitted from a remote hazard at the same time as a coded sound pulse sequence is emitted from this hazard.

5. The personal warning apparatus of claim 1 wherein the alarm indicator includes an audio warning speaker and / or warning lights.

6. The personal warning apparatus of claim 1 wherein the alarm indicator communicates with remote components or systems.

7. The personal warning apparatus of claim 1 wherein a valid coded sequence of received sound pulses is non-symmetrical about the midpoint of the sequence.

8. The personal warning apparatus of claim 1 wherein the sound pulses and time delay or delays in a valid coded sequence of received sound pulses have the same duration.

9. The personal warning apparatus of claim 1 wherein the sound pulses and time delay or delays in a valid coded sequence of received sound pulses have a total duration equal to four times the duration of a sound pulse or time delay.

10. The personal warning apparatus of claim 1 wherein the duration of a sound pulse or time delay is set to the expected travel time of a sound pulse emitted at a maximum operational range.

11. The personal warning apparatus of claim 1 wherein for a valid coded sequence of received sound pulses the first half of the coded sequence includes a sound pulse followed by a time delay and the second half of the sequence including two consecutive sound pulses.

12. The personal warning apparatus of claim 1 wherein for a valid coded sequence of received sound pulses the first half of the sequence includes two consecutive sound pulses and the second half of the sequence includes a time delay followed by a sound pulse.

13. A hazard mounted warning apparatus configured for engagement with a hazard, the apparatus includingat least one sound emitter, anda controller configured to activate the sound emitter to emit a coded sequence of sound pulses and time delays between sound pulses, each of the sound pulses and time delays having the same duration,the coded sequence being made up of a plurality of pulses and at least one time delay.

14. The hazard mounted warning apparatus as claimed in claim 13 wherein the starting or ending half of the coded sequence of sound pulses and time delays includes an identified sound pulse and a time delay, and the other half of the sequence including two consecutive identified sound pulses.

15. The hazard mounted warning apparatus as claimed in claim 13 wherein the coded sequence of sound pulses and time delays is non-symmetrical about the midpoint of the sequence.

16. The hazard mounted warning apparatus as claimed in claim 13 which includes a radiofrequency transmitter operated by the controller to transmit a timing signal at the same time as the sound emitter starts to emit the coded of sound pulses and time delays.

17. The hazard mounted warning apparatus as claimed in 13 wherein the coded sequence of sound pulses and time delays has a total duration equal to four times the duration of a sound pulse or time delay.

18. The hazard mounted warning apparatus as claimed in claim 13 wherein the duration of a sound pulse or time delay is set to the expected travel time of a sound pulse emitted at a maximum operational range.

19. The hazard mounted warning apparatus of claim 13 wherein the first half of the coded sequence of sound pulses and time delays includes a sound pulse followed by a time delay and the second half of the sequence including two consecutive sound pulses.

20. The hazard mounted warning apparatus of claim 13 wherein the first half of the coded sequence of sound pulses and time delays includes two consecutive sound pulses, and the second half of the sequence includes a time delay followed by a sound pulse.

Images