Emergency signalling in hazardous areas

The increasing use of signalling devices to enhance safety in the workplace is particularly important in petrochemical and oil and gas facilities, where the potential for serious accidents is far greater than in most other industrial environments. Neal Porter of E2S Warning Signals discusses safety concepts and suitability for alarms and signalling equipment in hazardous areas, and offers some practical guidance on their use in these locations.

Hazardous areas are defined as areas where concentrations of flammable gases, vapours or dusts may occur, either constantly (Zones 0 and 20), under normal operating conditions (Zones 1 and 21) or unusually (Zones 2 and 22). A whole series of additional conditions relating to the temperature classification and the auto-ignition temperatures of the type of gas or dust to be found to ensure that any equipment will not initiate an explosion or fire. Products designed for hazardous locations have to meet ever increasing standards and regulations. ATEX is the key requirement for Europe, while in North America, UL standards apply. In other parts of the world, particularly Australia, IECEx is gaining increasing acceptance. As well as these globally recognised standards, there are many local fire approvals that usually have to be met.

Given the variety of different gases or dusts that are potentially present in a hazardous area, detailed standards have evolved to ensure that all eventualities are taken into account when equipment is to be installed and operated in such an environment.

Products for use in hazardous areas

Hazardous area products fall into two categories. They either prevent an explosion by constraining the amount of energy entering the device (intrinsically safe) or have a sufficiently robust housing to contain an internal explosion (explosion proof). In most cases, they offer a robust, weatherproof device capable of operating reliably in the harsh environments in which they are often installed.

Materials

Four main enclosure materials are available for intrinsically safe and explosion proof products, offering different impact resistance, corrosion resistance and temperature ranges. UL94V-0 flame retardant plastic ABS enclosures for intrinsically safe (IS) units are light weight, impact resistant and corrosion proof. IS sounders and sounder/beacon combinations are also available in marine grade aluminium with a phosphate and powder coat finish housing that offers enhanced mechanical, temperature and UV protection compared with traditional plastic bodied devices.

Explosion proof devices are typically also housed in more robust enclosures, which give the necessary strength to contain an internal explosion. There are three main materials in use today. Aluminium alloy, glass reinforced plastic (GRP) and stainless steel; the choice is down to customer preference and the environment into which they will be installed.

A recent addition to the choice of materials is polyphenylene sulphide (PPS), an engineering plastic which can be moulded, extruded or machined to high tolerances to give a non-sparking, lightweight, corrosion proof housing suitable for use in Zone 2 and 22 applications.

Intrinsically Safe

Intrinsically safe products will have been designed for Zone 0 (gas) and Zone 20 (dust) and can therefore be used in Zones 1, 2, 21 and 22 as well. They generally use standard moulded enclosures and the protection comes from the electronics which is specially designed to limit the amount of energy required to initiate an explosion. Powered through a Zener barrier or galvanic isolator, they offer a very safe solution which is easy to install, but the limited amount of energy means that IS devices will only ever have lower performance than the same device installed in a safe area. Typically, sounders will have an output between 90dB and 105 dB @ 1m and beacons will use low power LED warning lights rather than ultra-bright Xenon strobes.

This limitation means that while they can be used outdoors in a plant, the sounder outputs are not sufficiently loud to be audible above the background noise. Consequently, IS products are usually best installed indoors in storage facilities, pharmaceutical plants and control rooms and indoor fire alarm systems which cover hazardous areas.

Explosion Proof

The input power to explosion proof products is not limited, so outputs are typically much higher than intrinsically safe devices. Safety is ensured because the devices are housed in rugged enclosures that will contain any potential explosion which may occur inside. This means they are heavier and more difficult to install than their IS equivalents, but they can have significantly higher outputs. For example, alarm sounders can be up to 120 dB @ 1m and beacons can incorporate powerful xenon strobes giving an effective light output up to 500 cd.

A LED intrinsically safe beacon may only warn people within a few metres of its location, but a 21 Joule explosion proof Xenon beacon has an effective warning distance of up to 35 metres. More importantly, the high intensity flash will reflect off any surfaces and will get attention even if one is not looking directly at it, an especially important consideration in a plant environment where personnel will be concentrating on their work and need to know if there is an emergency.

These products are the mainstay of fire alarm, gas detection and PA systems on large petrochemical installations around the globe where gas is the primary hazard. Increasingly, warning devices are being installed in sugar processing plants, grain storage facilities and other areas where dust, rather than gas, is the main explosive hazard. Obviously, any equipment installed in such areas must be certified for use in Zone 20, 21 or 22 areas.

Increased Safety

Many locations are classified as Zone 2 and it is possible to install alarm devices which have been designed specifically for these areas. This means that high performance products which are easier to install and have a lower purchase cost can be specified. Surprisingly, while there is a strong cost-benefit case to be made for this kind of product, the vast majority of Zone 2 areas are populated by Zone 1 products; it seems that designers adopt a cautious approach when specifying.

Choosing an effective alarm

Safety Integrity Level, SIL

Safety Integrity Level, SIL, is a measure of safety system performance expressed in terms of probability of failure on demand (PFD). In the oil and gas industry, particularly in the fire and gas detection systems where safety integrity is crucial to ensuring the safety of the plant, personnel, production and the environment, SIL 2 is becoming a common standard across systems. To meet the growing demand in the oil & gas industry, fault monitoring technology to give SIL compatibility is becoming increasingly common in explosion proof sounders and beacons from leading manufacturers such as E2S Warning Signals.

In large petro-chemical installations safety-critical warning devices are installed over large distances, so central monitoring is a key requirement. While fire and gas detection systems continually monitor the integrity of the cabling, the warning devices themselves are not checked continuously and physical inspections must be arranged to ensure these work properly. The new SIL 2 functionality in sounders and beacons means that each single device can be remotely checked and an alert sent to the control panel in case of fault.

A smart combination of software and hardware removes the need for time-consuming inspections and test of each individual warning device by intelligently reading the sound output of the sounder or the light emitted by the beacon to check it is working properly.

Beacons and Status Lights

There are a number of different ways that can be used to generate light and for emergency signalling: it is important to know the advantages and disadvantages of each type to make the right choice.

Rotating mirror beacons are by far the most effective, and are still used extensively today, particular for vehicles and moving machinery. Their high output light reflects off everything but the use of halogen lamps (around 200 hours of working life) and a mechanical drive system mean they need regular maintenance and are generally not suited to hazardous areas, especially where maintenance rules requires the system to be powered down each time work needs doing.

Xenon strobes, especially the higher power versions, have a working life beyond 2,000 hours and create an effect almost as good as the rotating mirror beacons which means they are the preferred choice for critical alarm systems such as fire, gas and PA.

There is a lot of interest in LED technology at the moment and the benefit of long life and the low maintenance and life costs they bring. Even the brightest units fall well below the outputs of a xenon strobe and so they are best used as status lights. They are particularly beneficial when used as “system good” green indicators, which are often working 24/7. The steady light, low power consumption and long working life are real benefits.

Alarm Sounders

These form the main backbone of most alarm systems, and many countries have national alert tones for fire alarm which are a legal requirement. France for example has the AFNOR tone, Germany the DIN tone and there are the PFEER tones for the offshore industry.

The choice of tone is very important. Continuous tones can very quickly blend into the background noise of motors, compressors and steam and do not grab your attention in the way a changing frequency tone does. The German DIN tone, which is also one of the PFEER tones, is particularly effective. It sweeps from Hz down to 500Hz every 1 second and can be heard at far greater distances than many other tones.

Electronic sounders can often generate up to 64 alarm tones, and many devices allow the use of three or four different stages of alarm, meaning that there can be a fire, toxic gas or any other kind of alarm from a single device. This allows greater functionality from each device and saves money on cabling and installation.

Typically, hazardous area alarm sounders have outputs of between 110 and 120 dB @ 1m. To create effective warning, the sound level needs to be at least 5 dB above the background noise and together with a choice of suitable tones, an effective alarm is created. When using several different signals for different alarms, it is important that the two or three tones selected are different and can be readily distinguished by plant personal as a quick response in an emergency is vital.

As well as electronic alarm tones, there are the traditional electro-mechanical products such as bells, buzzers and sirens, which are rich in harmonic content, very effective and easily recognisable. While widely used for more than 100 years, the reliability, performance, maintenance and running costs of electro-mechanical devices has always been a concern, particularly now that more efficient alternatives are available. Compared with solid state technology, electro-mechanical devices suffer from high inrush current on start up, require higher operating currents when running while being less efficient in terms of converting electrical to acoustic energy and will fail far sooner than an electronic alternative. Fortunately, digital electronics can now replicate these tones with complete fidelity and often with outputs that are higher than the originals. Solid state electronics ensure greater reliability and, most importantly, they are available in both heavy duty weatherproof and Ex versions.

Disaster Sirens

It is becoming more and more common for large industrial sites to extend their warning systems to cover car parks and storage facilities to provide a disaster siren for major emergencies and toxic gas release. This can be to warn both people on-site and also people living and working in the neighbouring areas adjacent to the plant. Sometimes the requirements are for a short distance (200 to 400 metres) and for others it is for far greater distances, possibly up to 2 km or more.

Typical solutions now have battery back-up, silent test and options for various communication methods including TCP/IP, Radio Control, GSM and RS485 which means a siren can be installed and managed remotely from the control room without significant expense.

Disaster sirens require high power inputs for operation, and so they are usually installed in the safe areas. However, it is possible to have the electronics installed in an Ex d enclosure and mount the speakers at 15 metres which is usually classed as safe area, giving the best of both worlds.

High quality voice reproduction can also be achieved using these products, giving the option of extending the site PA systems to cover other areas.

Temporary Alarms

As well as the usual requirements for fixed safety warning devices on an established plant, there is increasing use as temporary alarms, especially during the construction phase of a new or extended plant. Radio control makes this an easy to implement solution, and with only a small ac power supply required or powered from solar panels, it can be up and running quickly and then moved to another site once the construction phase is complete.

This gives the construction engineers the option of a full fire alarm and/or emergency management system which can be activated from almost anywhere in the plant without any cabling, providing a temporary solution which is as effective as a fixed installation.

An overview of hazardous area definitions

A more detailed information bulletin on hazardous areas can be downloaded as a PDF from www.e2s.com/system/hazardous-area-guide. It gives details of gas and dust groups, temperature classifications, common flammable gases, vapours and dust types, ATEX, IECEx and North American protection concepts and many other useful references in a convenient single overview document.

If you want to learn more, please visit our website SAFER-Ex.

Contact Details and Archive...

The present invention relates generally to signaling devices used in Class I, Division I explosion-proof hazardous locations, and more particularly, to visual signaling devices that emit attention attracting light signals, and yet retain their various color identification.

Studies of light signaling devices used in industrial and commercial areas as well as on industrial equipment show that effective warning is best accomplished by signaling devices, which combine a bright visual light signal with high color identification. Color identification is highly desirable in light signaling devices because red, blue, green, and amber colored light signals have long become associated with stop, start, warning, and waiting indication in industrial and commercial application.

Elevated industrial signaling devices are well known in factory-type environments where numerous industrial machines are present. Generally, such industrial signaling devices are mounted on a pole so they are high above each machine and clearly visible from a distance. Each device typically has a plurality of modules that emit differently colored light for visually signaling the operating status of each machine.

In a typical signaling device, each of the lights is responsive to an operating status of the machine to which the device is connected. For example, a typical device has lights of various colors such as, blue, red, amber and green. Each of the these differing colors is contained in a discrete module. The differing colors of the lights correspond to various operating stages of the machine. For example, a blue light may indicate the machine is running correctly, an amber light may indicate that the machine is in need of service and a red light may indicate that the machine has ceased operating. The colors of the lights are very important because even at a distance an illuminated light of one color is immediately distinguishable from the other lights of different colors.

FEDERAL SIGNAL of University Park, Illinois has Model 121X which is a rotating light which flashes 90 times per minute and produces a 360° visual signal. This explosion-proof light has an incandescent lamp and is available in five separate lens colors—amber, blue, clear, green and red. This device is ideal for use in indoor and outdoor areas such as oil rigs, mines refineries, and chemical plants.

FEDERAL SIGNAL also has a Model FB2PSTX explosion-proof strobe light which is a compact unit that produces a “lightening bolt” flash of light. This device has an outer dome made of tempered glass. Polycarbonate inner lenses are available in amber, blue, clear, green and red.

FEDERAL SIGNAL has a Model 27XST which is an explosion-proof strobe light which produces 80 high-intensity flashes per minute. This device is also ideal for use in areas such as oil rigs, mines, refineries, and chemical plants. The interior lens of this device is available in amber, blue, clear, green, red and magenta.

It should be noted however, that none of the above-noted FEDERAL SIGNAL devices is capable of multiple color displays without the need for a colored interior lens.

Another examples of these devices is U.S. Pat. No. 5,103,215 to James et. al which discloses a signaling light made from a plurality of differently colored vertically stacked modules with incandescent lights. The cover lens of each module may be removed separately and the bulbs in each module may be replaced without having to disassemble the entire piece.

In addition, U.S. Pat. No. 5,769,532 to Sasaki discloses a LED signaling light made from a plurality of differently colored vertically stacked modules. Each module contains a portion bulged outwardly, which is coated with a reflective material. The LEDs are arranged in rows so that their emitted light is reflected off the reflecting surface and projected into the environment surrounding the module.

Moreover, U.S. Pat. No. 5,929,788 to Vukosic discloses a LED signaling device where clusters of LEDs arranged in rings are mounted on a circuit board and emit light on to a conical reflective surface. The conical reflective surface is outwardly flaring. In order to change to color of the emitted light different colored covers must be manually changed.

Elevated signaling devices are particularly effective in environments where the level of background noise is very high and there is a danger that an audible alarm will not be heard. Furthermore, the elevated signaling devices can distinguish between various malfunctioning conditions by relating different conditions to different colors of lights or to different frequencies of flashing lights. In a crowded factory, a system of elevated signaling devices enables maintenance people to quickly locate and identify specific problems in a large number of operating machines. Such a system is extremely effective and efficient because it enables a single individual to monitor a large number of machines from a distance where the operating status of all the machines can be simultaneously observed.

While these elevated signaling devices have proven to be very effective, they also have various disadvantages. Typical devices are made with a plurality of modules, where each module illuminates a different colored light. A design of one color per single module has numerous disadvantages.

One such disadvantage is when the manufacturing operation takes place in a clean room, such as in the manufacture of semiconductor devices. In order to have better environmental control, it is desirable to reduce the volume of the clean room as much as possible. Industrial signaling devices that employ multiple modules are often too large to be used in clean rooms that have reduced height. Also, multiple module lights have numerous interfaces between the lens of the light and the housing of the electrical components. Each connection interface is a weak spot where water, liquid, dust, corrosive materials, etc. can enter the light and ruin electronic components. Moreover, the manufacture of such multiple module lights is wasteful, and sometimes assembly of the multiple modules is required by the end user. Multiple modules require greater storage space and can be more expensive to handle and ship. They are also more cumbersome to install or service and this can be difficult when the multiple modules are at the end of a pole ten feet or more above a factory floor. Usually, a maintenance person climbs a ladder in order to reach the signaling device.

Accordingly, it is desirable to provide a method and apparatus that has the capability to provide the needed visual signals in a single multi-color changeable device resulting in greater versatility and functionality while maintaining its integrity in a hazardous environment.

The foregoing needs are met, to a great extent, by the present invention, wherein in one aspect an apparatus is provided that in some embodiments a single multi-color changeable signal device for use in hazardous or explosive environments is provided.

In accordance with one aspect of the present invention, an explosion-proof industrial signaling device is provided comprising a single lens module; at least one light source contained within the module, wherein the light source includes a plurality of clusters the clusters which are disposed spaced apart from one another, each of the clusters containing lights of different colors which are independently activated such that a signal is seen to be emitting from a signal housing as an individual color.

In accordance with another aspect of the present invention, an explosion-proof industrial signaling device is provided comprising a single module means for protecting a light source, whereby the light source includes a plurality of light clusters, the clusters which are disposed spaced apart from one another, each of the clusters containing lights of different colors which are independently activated such that a signal is seen to be emitting from a signal housing an individual color, and a plurality of light sources disposed in a spaced apart arrangement and located at a focal point of the single module means of the signal housing.

In accordance with still another aspect of the present invention, a method for processing visual indicator signals of an explosion-proof industrial signaling device is provided comprising the steps of utilizing incoming analog information to enable an LED cluster assembly to light, decoding one PLC input to light one LED cluster, and decoding at least two PLC inputs to light at least two LED clusters of differing colors.

There has thus been outlined, rather broadly, certain embodiments of the invention in order that the detailed description thereof herein may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto.

In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.

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FIG. 1 is an exploded view illustrating an explosion-proof visual signal device of a preferred embodiment of the invention.

FIG. 2 is an exploded view of a subassembly of the explosion-proof visual signal device.

FIG. 3 is a diagrammatic view illustrating a wall mounted explosion-proof visual signal device.

FIG. 4 is a diagrammatic view illustrating a ceiling mounted explosion-proof visual signal device.

FIG. 5 is a diagrammatic view illustrating a pendant mounted explosion-proof visual signal device.

FIG. 6 is a schematic of the PLC circuit for the explosion-proof visual signal device.

FIG. 7 is a diagrammatic view illustrating a jumper pin assembly for the explosion-proof visual signal device.

FIG. 8 is a diagrammatic view illustrating the jumper pin assembly of FIG. 6A of the explosion-proof visual signal device.

FIG. 9 is a top view of the LED configuration mounted within the explosion-proof visual signal device.

FIG. 10 is a side view of FIG. 9 along line A-A showing the LED configuration of the explosion-proof visual signal device.

FIG. 11 is a cross-sectional top view of FIG. 2 of the assembled explosion-proof visual signal device.

The invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. An embodiment of the present inventive apparatus and method is illustrated in FIG. 1. This embodiment in accordance with the present invention provides an explosion-proof multi-color, multi-status signaling device 100 having an effective balance between signal brightness and color identification provided by placing a light emitting diode (LED) light source or cluster 140 in red, blue, and amber or in red, green, and amber in front of a highly reflective material 905 that amplifies and distributes the light output. The LED light source or cluster 140, the reflector 905, and all associated electronics are housed in the top end of a heavy-duty explosion-proof housing 110, preferably made of cast aluminum. This housing 110 is connected to a glass dome or lens 130 via a ring mount 135. The glass dome is preferably made of a polycarbonate material. An exterior guard 120 encased the glass dome 130 to add additional protection.

Referring to FIG. 2, the explosion-proof multi-color, multi-status signaling device 100 may be mounted to various types of mounts with mounting screws 220 and gasket 210. A programmable logic control (PLC) unit 200 may be internal to the signaling device 100 in order to operate the LED light cluster 140.

Referring to FIGS. 3-5, it is anticipated that the multi-color, multi-status signaling device 100 including housing 110 may be mounted in at least three arrangements. A wall mount 300 shown in FIG. 3, a ceiling mount 400 shown in FIG. 4, or a pendant mount 500 shown in FIG. 5. These various mounting options may be incumbent upon the required use and location of the multi-color, multi-status signaling device 100.

Referring to FIG. 6, the multi-color, multi-status signaling device 100 may be configured with an internal microprocessor PLC sinking output circuit 600 or without an internal microprocessor PLC circuit utilizing instead an external PLC (not shown). The embodiment of the multi-color, multi-status signaling device 100 having the internal microprocessor PLC sinking output circuit 600 interprets incoming analog information to enable the LED light cluster 140 to light according to the input or information provided.

Referring to FIGS. 7 and 8, the multi-color, multi-status signaling device 100 may also have an internal jumper 700 with associated jumper pins 710 connected to a circuit board 810 having a circuit board power connector interface 800. This jumper 700 may allow the first selected light to illuminate as either a steady or flashing light. For example, if jumper pins 710 has jumper 700 on pins 1 and 2 a flashing light may be enabled while having jumper 700 on pins 2 and 3 enables a steady light configuration.

Referring to FIGS. 9-11, the LED light source or cluster 140 may include a printed circuit board 900 connected to circuit board 810 and configured as a three-sided vertical structure to illuminate the LED light cluster 140 in a 360° hemi-spherical range. A reflective material 905 is disposed adjacent to LED light cluster 140 to increase the illumination upon activation of LED light cluster 140. The printed circuit board contains an array of red LEDs 910, an array of blue or green LEDs 920 and an array of amber LEDs 930.

The explosion-proof visual signal device 100 provides a rugged case enclosing the necessary elements of proper operation of the signal lights and isolating these elements from any explosive external atmosphere which may exist via glass dome 130.

In operation, the internal microprocessor embodiment utilizes incoming analog information to cause the LED light cluster 140 to illuminate. For example, if the microprocessor PLC unit 200 detects one contact closure for PLC input, then one selected LED cluster 910, 920, or 930 will illuminate. If two or more PLC inputs or contact closures are received, then microprocessor PLC unit 200 decodes this information and causes the light to cycle between two or more selected LED clusters 910, 920, or 930.

In an alternative use for the present invention, it should be noted that the housing 110 may be moisture-proof allowing the signal lights or cluster 140 to be used in damp environments or outdoors where various weather conditions may occur.

In another embodiment, the multi-color, multi-status signaling device 100 without the internal microprocessor PLC unit 200 functions in the same manner as the signaling device 100 with the microprocessor PLC unit 200 with the exception that all functionality is controlled by inputs from an external PLC (not shown). Therefore, each color of the LED light source or cluster 140 can be separately activated through an external contact closure or input from an external industrial programmable logic controller.

The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.

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