Sounders, beacons and combination units communicate alarms and equipment conditions in different ways. A sounder produces an audible warning, a beacon provides a visual signal, and a combination unit brings both warning methods together within one assembly.
The correct choice depends on who must receive the warning, the surrounding noise and lighting conditions, the required alarm response and the hazardous area classification.
Thorne & Derrick supplies a comprehensive range of hazardous area sounders, beacons and combination units for audible, visual and combined signalling in potentially explosive atmospheres.
Quick answer: select a sounder where personnel must hear the alarm, a beacon where they must see it, and a combination unit where audible and visual warning should be provided from the same signalling point. The final choice must follow the site alarm philosophy and hazardous area specification.
| Device | Warning Method | Main Strength | Potential Limitation | Key Selection Data |
|---|---|---|---|---|
| Sounder | Audible alarm tone, horn or bell | Can alert personnel who are not looking towards the device | Recognition can be affected by high noise, distance or hearing protection | Sound output, tone, frequency, coverage, voltage and current |
| Beacon | Visual light signal | Provides a visible warning or persistent status indication | Requires a suitable line of sight and sufficient contrast | Light source, signal mode, colour, visibility, voltage and current |
| Combination Unit | Audible and visual signals | Provides two warning methods from one signalling location | Electrical demand, control logic and certification can be more complex | Sounder data, beacon data, input arrangement, mounting and total load |
Important: a combination unit is not automatically required for every alarm. The selected warning method should be based on the risk assessment, alarm philosophy, personnel needs and environmental conditions.
A sounder is an audible signalling device that produces a tone, horn, siren or bell output when activated.
The signal can warn personnel of an emergency, communicate an evacuation instruction, indicate an equipment condition or distinguish between different alarm states.
Sounders are commonly specified using a sound-pressure level stated in dB(A) at a defined distance. The test distance and tone should be checked because output can vary between tone settings.
A higher stated sound output does not automatically guarantee that the alarm will be understood throughout the area. Machinery noise, walls, pipework, distance, hearing protection and the frequency content of the alarm can all affect recognition.
Many electronic sounders provide several selectable tones. The chosen tone should remain recognisable against the background noise and distinct from other plant alarms.
Explore ATEX sounders for hazardous area audible warning.
A beacon is a visual signalling device that uses light to communicate an alarm, warning, process event or equipment status.
Depending on the product, the visual output may be steady, blinking, flashing, strobe or rotating. LED, xenon, filament and fluorescent technologies can be available.
Beacon visibility is influenced by the optical output, signal pattern, lens colour, ambient lighting, mounting position, viewing distance and surrounding obstructions.
A beacon may be particularly useful where personnel wear hearing protection, the background noise is high or a persistent visual status must remain available.
Explore ATEX beacons for hazardous area visual signalling.
A combination unit provides audible and visual warning from one assembled signalling point.
The sounder and beacon may be incorporated within one enclosure or assembled together on a common mounting plate. Backplate-mounted units can combine separate certified sounder and beacon products into one pre-arranged assembly.
Some combination units are pre-wired so that one input activates the sounder and beacon simultaneously. Other configurations can provide separate inputs or multi-stage control, allowing the audible and visual signals to operate independently.
The required input arrangement must therefore be confirmed before ordering. It should not be assumed from the product description alone.
Explore hazardous area sounder-beacon combination units.
Audible warning performance depends on more than the sounder’s maximum stated dB(A) output.
Consider:
Where the audible alarm could be masked or misunderstood, a beacon or combination unit may provide an additional visual warning method.
A beacon must be positioned so that the intended personnel can see and interpret its signal from the required working locations.
Consider:
Read Steady vs Flashing vs Rotating ATEX Beacons for a comparison of visual signal modes.
The alarm-system design must support the selected product’s voltage, current consumption, switching and monitoring requirements.
| Control Requirement | Sounder | Beacon | Combination Unit |
|---|---|---|---|
| Electrical load | Sounder current at selected voltage and tone | Beacon current for selected colour and signal mode | Combined or independently switched load |
| Inputs | Single-stage or multi-stage tone activation | Fixed, selectable or remotely controlled mode | Common input or independent sounder and beacon inputs |
| Monitoring | Confirm system supervision and end-of-line requirements | Confirm monitoring compatibility and polarity | Confirm supervision for both circuits or the combined assembly |
Do not assume simultaneous operation: some combination units use one common input, while others support independent or multi-stage activation. Confirm the wiring arrangement from the current product documentation.
Sounder, beacon or combination-unit selection must begin with the complete hazardous area specification.
Check:
Read the guide to ATEX and IECEx certification of hazardous area equipment.
See also hazardous area zones and explosive atmosphere classification.
Hazardous area certification does not automatically establish suitability for every outdoor, offshore, marine or corrosive location.
Review:
| Question | Selection Consideration |
|---|---|
| Who must receive the warning? | Personnel location, duties, hearing protection and line of sight |
| What response is required? | Evacuate, stop, investigate, acknowledge or continue normal operation |
| Is the area noisy? | Check whether an audible signal will remain recognisable |
| Is the beacon visible? | Assess mounting, viewing distance, lighting and obstructions |
| Are both signals required? | Determine whether separate or combined devices are more suitable |
| How will the unit be controlled? | Single input, independent inputs, multi-stage operation and monitoring |
| What is the hazardous area? | Zone, atmosphere, group, temperature and complete certification |
| What environment will it face? | Outdoor, offshore, chemical, dust, corrosion, vibration and temperature |
Not automatically. A beacon provides a visual signal while a sounder provides an audible signal. The required alarm method should be determined by the risk assessment and alarm philosophy.
Not in every application. It provides two notification methods, but coverage, positioning, control, electrical load and the required personnel response must still be assessed.
Some combination units support independent or multi-stage control, while others use one common input. The required arrangement must be confirmed before ordering.
No. The tone must be audible and recognisable in the intended area without creating unsuitable sound levels. Background noise, distance and frequency are all relevant.
A visual signal can support alarm recognition in high noise, but its visibility and line of sight must also be assessed. A combination of warning methods may be appropriate.
No. Zone suitability is determined by the complete equipment certification and marking, not by whether the product is audible, visual or combined.
Send Thorne & Derrick the hazardous area classification, required warning method, sound and visibility conditions, voltage and installation environment for product selection support.
Explore audible, visual and combined warning devices for Zone 1, Zone 2, Zone 21 and Zone 22 installations.
Ex d, Ex e and combined Ex d e markings describe different methods of protecting electrical equipment intended for use in potentially explosive gas atmospheres.
An Ex d beacon uses a flameproof enclosure designed to contain an internal ignition and prevent flame propagation into the surrounding atmosphere. Ex e increased safety uses additional construction measures intended to avoid arcs, sparks and excessive temperatures under the certified operating conditions.
A product marked Ex d e or Ex db eb combines these protection concepts in different parts of the equipment. For example, the optical and electronic components may be housed within a flameproof chamber while the field-wiring terminal compartment uses increased-safety protection.
Thorne & Derrick supplies a comprehensive range of hazardous area visual signalling devices with flameproof, increased-safety and combined protection arrangements.
For a general introduction to visual signalling in potentially explosive atmospheres, read What Is an ATEX Beacon?
Key distinction: Ex d is designed to contain an internal explosion. Ex e is designed to avoid ignition-capable faults through increased constructional safety. A combined Ex d e product applies the appropriate concept to different parts of the equipment.
| Protection | Principle | Typical Beacon Application | Important Installation Consideration |
|---|---|---|---|
| Ex d / Ex db | Contains an internal explosion and controls flame propagation through designed flamepaths | Optical chamber, lamp housing or electronics enclosure | Flamepaths, threads, fasteners and certified cable entries must remain compliant |
| Ex e / Ex eb | Uses additional measures to avoid arcs, sparks and excessive temperatures | Terminal compartment and field-wiring connections | Terminal capacity, conductor preparation, clearances and connection security are critical |
| Ex d e / Ex db eb | Applies flameproof and increased-safety concepts to different equipment sections | Flameproof signalling chamber with a separate increased-safety terminal compartment | Both protection concepts and their associated installation requirements must be maintained |
Do not interpret the marking in isolation: Ex d, Ex e or Ex d e does not by itself confirm the permitted zone, gas group, temperature class, ambient range or dust suitability. The complete equipment marking and certificate must be checked.
An Ex d flameproof enclosure is designed on the basis that an explosive gas atmosphere may enter the enclosure and could be ignited by an internal component.
The enclosure is constructed to withstand the pressure created by an internal explosion. Joints and openings are engineered as flamepaths that cool escaping gases sufficiently to prevent the explosion from propagating into the external atmosphere under the certified conditions.
Ex d does not mean that an explosion can never occur inside the enclosure. Its protection principle is based on containment and controlled flame transmission.
Flamepaths can be formed by threaded joints, cylindrical joints, flanged joints or other certified enclosure interfaces.
Their dimensions, finish and condition form part of the certified design. Flamepaths must not be drilled, filed, painted, damaged or modified outside the manufacturer’s permitted procedures.
Where the cable enters directly into a flameproof enclosure, the gland, adaptor or stopping plug must be appropriate for the certified entry arrangement, cable type and installation.
An unsuitable cable gland or unapproved modification can compromise the complete protection concept even when the beacon itself carries the correct marking.
Flameproof equipment is sometimes described using the general term “explosion proof”. This can lead to misunderstandings about what the construction provides.
Ex e increased safety uses additional construction measures intended to prevent ignition-capable arcs, sparks and excessive temperatures under the certified operating conditions.
Unlike Ex d, an increased-safety enclosure is not based on containing an internal explosion. Equipment and components are selected so that an ignition source is not expected to develop within the protected section during normal service.
On a combined beacon, Ex e is frequently applied to the terminal compartment. This allows the incoming supply cable to be connected without opening the separate flameproof electronics or optical chamber.
The terminals, conductor sizes, stripping lengths and cable-entry equipment must still follow the manufacturer’s instructions and certificate conditions.
Important: Ex e does not make loose strands, incorrect conductor sizes or poorly tightened terminals acceptable. Correct workmanship forms an essential part of maintaining increased-safety protection.
Combined Ex d e protection means that different sections of the same beacon use different protection concepts.
A typical arrangement includes:
The LEDs, lamp, xenon tube, power electronics or energy-storage components are contained within an Ex d or Ex db enclosure.
The incoming cable and supply conductors terminate within a separate Ex e or Ex eb compartment using increased-safety terminals and entry equipment.
The marking does not mean that every component is simultaneously protected by both concepts. It identifies a certified assembly incorporating more than one method of protection.
Product literature and certificates can use different marking formats depending on the applicable standard edition and approval.
Older or simplified documentation may show:
More detailed markings can include an additional protection-level suffix:
Always use the exact marking shown on the product certificate and equipment label. Do not rewrite or assume a marking based only on a catalogue heading.
The protection concept forms only one part of the complete hazardous area marking.
Ex db eb IIC T6 Gb
Illustrative marking format only. Refer to the actual product certificate and label.
| Marking | General Meaning |
|---|---|
| Ex | Equipment uses a recognised explosion-protection concept |
| db | Flameproof enclosure protection, level “b” |
| eb | Increased-safety protection, level “b” |
| IIC | Gas group shown in this illustrative example |
| T6 | Gas temperature class shown in this illustrative example |
| Gb | Equipment protection level for a gas atmosphere |
The complete marking may also include the equipment group, category, certificate number, permitted ambient range, ingress protection and special conditions of use.
Read the wider guide to ATEX and IECEx certification of hazardous area equipment.
Ex d and Ex e are protection concepts associated with explosive gas atmospheres. They do not, by themselves, confirm suitability for combustible dust.
A beacon certified for Zones 21 and 22 will normally carry a separate dust marking. This may include protection by enclosure such as Ex tb, together with a dust group, maximum surface temperature and equipment protection level.
| Atmosphere | Example Protection Concepts | Zones Commonly Associated |
|---|---|---|
| Gas, vapour or mist | Ex d, Ex e, Ex d e and other gas protection concepts | Zones 0, 1 and 2, subject to the complete marking |
| Combustible dust | Ex t or Ex tb protection by enclosure and other applicable concepts | Zones 20, 21 and 22, subject to the complete marking |
See the guide to hazardous area zones and explosive atmosphere classification for further information about gas and dust zones.
These product families demonstrate how different protection arrangements can be applied to visual signalling equipment. Always confirm the current certificate and exact ordered configuration.
The FB11 filament and FL11 fluorescent steady-beacon range uses flameproof construction. Current marking and temperature classification depend on the selected certified variant.
The dSLB20 LED combines a flameproof aluminium signalling housing with an increased-safety terminal compartment.
The dSLB20 xenon strobe also uses a flameproof signalling enclosure with a separate increased-safety terminal arrangement.
Installation must follow the manufacturer’s instructions, certificate conditions, applicable standards and site procedures.
Installation, inspection and maintenance should be completed by suitably competent personnel familiar with hazardous area equipment and the relevant protection concepts.
| Inspection Area | Ex d Focus | Ex e Focus |
|---|---|---|
| Enclosure | Damage, corrosion, cracks and pressure-containing integrity | Damage, ingress, corrosion and environmental protection |
| Joints | Flamepath condition, threads, covers and fasteners | Gaskets, covers and protection of terminal clearances |
| Connections | Certified entry system and internal connection integrity | Terminal security, conductor condition and insulation |
| Modifications | Check for unauthorised machining or flamepath alteration | Check for unapproved terminals, links or wiring changes |
The protection concept should not be selected independently from the certified beacon design. The manufacturer determines the equipment construction and obtains approval for the complete product.
Product selection should instead confirm:
Read How to Select an ATEX Beacon for the complete product-selection process.
Ex d is the IEC flameproof protection concept. “Explosion proof” is often used as a general term, but the exact approval system, marking and technical requirements should always be confirmed.
The protection principle assumes an internal ignition may occur. The enclosure is designed to withstand it and prevent flame propagation into the external atmosphere under the certified conditions.
No. Increased safety is based on preventing ignition-capable arcs, sparks and temperatures. It is not designed on the basis of containing an internal explosion.
It can allow the field supply cable to be terminated in a separate increased-safety section without opening the main flameproof electronics or optical chamber.
Both identify flameproof protection. The additional “b” identifies the protection level within the more detailed marking format. Use the exact terminology shown on the relevant certificate.
Not from that marking alone. The complete equipment category, protection level, gas group, temperature class, ambient range and certificate must confirm suitability for the installation.
Only when it also carries appropriate combustible-dust certification and marking, such as the applicable Ex t or Ex tb protection details.
Send Thorne & Derrick the zone, gas or dust group, temperature requirements, signal type, operating voltage and installation conditions for product selection support.
Explore flameproof and combined-protection visual signalling devices with LED, xenon, steady, flashing and rotating configurations.
Mineral-insulated heat trace cable is generally considered when the required temperature, power output, circuit length or operating environment exceeds the practical capability of polymeric self-regulating or constant wattage cables.
To understand where MI fits within the wider technology range, see the guide to electrical trace heating technologies. This article focuses specifically on the selection conditions that justify an MI system.
MI cable is commonly considered for:
A mineral-insulated heater uses a metallic resistance conductor electrically insulated from a metal sheath by compacted mineral insulation, commonly magnesium oxide. The metal sheath provides mechanical and environmental protection while the conductor generates heat when current flows.
MI trace heaters may be supplied in single- or twin-conductor configurations and normally include engineered cold leads, joints and end terminations. The heating section is designed for the required resistance, voltage, length and output rather than cut freely from a reel on site.
MI cable is frequently selected where the operating or exposure temperature is above the rating of suitable polymeric heating cables.
The required maintain temperature and the maximum exposure temperature are different design values. Cable, joints, cold leads and terminations must all remain suitable for the highest credible operating, cleaning, upset or shutdown condition.
A system that must raise the temperature of a cold pipe, vessel or process product within a defined period can require substantially more power than a steady-state maintenance duty.
The starting point is an accurate heat-loss and heat-up assessment. MI cable may then be selected where a high engineered output is required and the equipment can safely accept the resulting sheath temperature.
High-output design must consider:
MI heating cable is a series-resistance heater. Its resistance, length, conductor material and supply voltage are selected together to produce the required output.
This engineered approach can be useful for long pipe runs or duties where parallel-circuit cable limits would require multiple shorter circuits. However, a long MI circuit is not automatically the best solution; voltage, output distribution, cold leads, power supplies and control architecture must all be assessed.
The metal sheath and mineral insulation can provide strong resistance to heat, fire and mechanical damage. Different sheath alloys are available for different corrosive environments.
| Environmental Requirement | Why MI May Be Considered |
|---|---|
| High ambient or process heat | Metal and mineral construction can tolerate temperatures beyond many polymeric cables |
| Mechanical exposure | Metal sheath provides robust protection, subject to routing and bend-radius limits |
| Chemical or corrosive atmosphere | A suitable sheath alloy can be selected for the environment |
| Fire resistance | Inorganic insulation and metal construction offer strong high-temperature stability |
| Outdoor or offshore service | Engineered sheath, joints and terminations can suit severe environments |
| High-pressure or critical process plant | Factory-engineered assemblies provide controlled resistance and documented construction |
Sheath selection must be based on the actual chemical exposure. No single metal alloy is universally resistant to every acid, chloride, sulphur compound or process contaminant.
MI heaters are available as certified systems for explosive atmospheres, but the complete assembly must be selected and installed for the area classification.
View the ATEX trace heating range and obtain technical confirmation for the proposed MI assembly.
| Selection Factor | Mineral-Insulated | Self-Regulating | Constant Wattage / Resistance |
|---|---|---|---|
| Typical reason for selection | High temperature, high output, long engineered circuit or severe environment | Variable-temperature response and convenient field installation | Defined output and controlled process heating |
| Construction | Metal conductor, mineral insulation and metal sheath | Parallel bus wires with conductive polymer core | Parallel heating zones or series resistance conductor |
| Field cutting | Normally supplied as an engineered heater unit | Usually cut to length within product limits | Depends on parallel-zone intervals or engineered series length |
| Local output response | No self-regulating response | Output changes locally with temperature | Defined output when energised |
| Temperature control | Engineered controller and often limiter required | May still require controller or limiter | Normally requires suitable control |
| Installation skill | Specialist handling, termination and testing | Commonly field terminated with approved kits | Depends on cable construction and system design |
For a detailed comparison of the two common polymeric cable types, see self-regulating vs constant wattage trace heating.
MI cable should not be specified simply because it is the most robust or highest-temperature technology available.
The preferred cable is the one that meets the thermal, electrical, environmental and certification requirements with appropriate control—not automatically the cable with the highest temperature or output rating.
Provide these details for design:
Explore the available mineral-insulated trace heating cables and engineered systems.
No. High temperature is a common reason for selecting MI, but high output, long engineered circuits, fire resistance, mechanical strength and chemical resistance can also influence the decision.
MI heaters are normally designed and manufactured to a specific resistance, length, voltage and output. They should not be treated as bulk cut-to-length parallel cable.
A suitable controller is normally required, and an independent temperature limiter may also be necessary where maximum sheath or surface temperature must be controlled. The exact arrangement comes from the system design.
Yes, certified MI heater systems are available. The complete assembly, controls, terminations and installation must match the area classification and certification conditions.
Its metal sheath and inorganic insulation can provide excellent heat, fire and mechanical resistance. Durability still depends on choosing the correct sheath alloy, installing it within bend limits and protecting joints and terminations.
Self-regulating cable may be more suitable for lower-temperature frost protection, irregular pipework, changing ambient conditions and projects requiring straightforward cut-to-length installation.
Thorne & Derrick supports mineral-insulated heating cable selection for high-temperature, high-output, long-line and hazardous-area applications.
Hazardous area beacon lens colours help personnel distinguish between alarms, warnings, equipment states and process conditions. Red, amber, green, blue and clear signals can each communicate a different message when used within a properly defined alarm philosophy.
However, a beacon colour does not have one fixed meaning in every industry or on every site. The intended response should be established through the project specification, operating procedures and site-specific visual signalling system.
Thorne & Derrick supplies hazardous area ATEX beacons in a range of lens and signal colours, with LED, xenon, steady, flashing, strobe and electronically rotating options.
For a general introduction to hazardous area visual signalling, read What Is an ATEX Beacon?
Key principle: select the beacon colour from the documented site alarm philosophy. Do not assume that a colour automatically represents the same condition across every plant, industry or country.
The table below summarises common industrial interpretations. These meanings are indicative only and must be checked against the site alarm philosophy.
| Beacon Colour | Common Interpretation | Example Applications | Required Response |
|---|---|---|---|
| Red | Danger, emergency, serious alarm or stop condition | Fire alarm, gas alarm, emergency shutdown or hazardous machine state | Immediate attention or action may be required |
| Amber or Yellow | Warning, caution, abnormal condition or awareness | Equipment about to start, process deviation, restricted area or potential hazard | Check conditions and proceed with caution |
| Green | Normal, safe, available, ready or action completed | Equipment operating normally, safe access or alarm acknowledged | Normal operation or a safe condition may be indicated |
| Blue | Change, specific status, instruction or security-related condition | Equipment powering down, security alarm or site-specific process state | Follow the documented site instruction |
| Clear or White | General attention, location, visibility or project-specific indication | General notification, obstruction indication or equipment identification | Confirm the intended meaning from the site documentation |
Do not rely on this table alone: the signal meaning should be formally defined, documented and communicated to site personnel. A manufacturer’s available colour does not determine how it must be used.
Red is commonly associated with danger, emergency, fire, a serious process alarm or a condition requiring immediate attention.
A flashing red beacon generally creates a stronger warning message than a steady red signal. However, the response must be determined by the documented alarm system rather than the colour and signal mode alone.
Avoid conflicting meanings: if red is reserved for fire or evacuation alarms, it should not also be used for routine equipment status without a clear and documented distinction.
Amber and yellow are commonly used for warnings, caution, abnormal conditions or situations requiring increased awareness.
The signal may indicate that equipment is about to start, a process is outside its normal range or a potential hazard is developing but has not reached an emergency condition.
Manufacturers do not always use amber and yellow terminology in exactly the same way. One datasheet may describe the lens as amber while another refers to the corresponding emitted LED colour as yellow.
Always use the exact manufacturer colour description and ordering code when requesting a quotation.
Green is commonly used to indicate a normal, safe, available or correctly operating condition.
It can also show that an alarm has been acknowledged, corrective action is under way or equipment is ready for operation.
Green should not be used where personnel could mistake it for an unrestricted safe condition when a residual hazard remains.
Blue is often used for a specific instruction, change in condition, security-related alarm or site-defined process state.
Its meaning can be particularly site-specific. Personnel should therefore be trained to understand the response required when a blue signal is activated.
External restrictions may apply: blue warning lights can have regulated meanings in transport and emergency-service environments. Check the installation location and applicable rules before selection.
“Clear” and “white” do not always describe the same component.
A clear or transparent lens describes the colour of the dome or cap. A white signal describes the light emitted by the LED, lamp or flash source.
A clear lens may therefore be used with a white LED, xenon flash tube or another internal light source, depending on the product.
Clear or white should not be treated as a neutral default without confirming what the signal is intended to communicate.
Personnel interpret the complete visual signal rather than the lens colour in isolation. A steady red light can communicate a different level of urgency from a rapidly flashing red strobe.
The meaning can be strengthened by combining colour with:
Colour should be supported by these supplementary methods where relying on colour alone could create ambiguity.
Read Steady vs Flashing vs Rotating ATEX Beacons for a comparison of the principal visual signalling modes.
Yes. The method used to create the coloured signal can differ between LED and xenon products.
An LED beacon can use coloured LEDs, a coloured cap or a combination of the two. The wavelength, brightness and current consumption can vary between colours.
A xenon flash tube produces a broad-spectrum pulse of light. A coloured dome or lens filters that light to create the required signal colour.
The filtering effect can reduce the measured optical intensity compared with a clear lens. The reduction is product- and colour-specific.
Read LED vs Xenon ATEX Beacons for a wider comparison of the two technologies.
Colour can affect the apparent brightness, contrast and recognition of a beacon signal.
Visibility is influenced by:
Product-specific performance: do not assume that one colour is always brighter than another. Current Eaton FHF dSLB20 LED data, for example, gives different approximate optical outputs for white, red, yellow, green and blue versions.
Where a warning is safety-critical, the meaning should not depend unnecessarily on colour alone.
Lighting conditions, smoke, dirt, distance and differences in colour perception can all affect how the signal is recognised.
Supplementary methods can include:
Explore the wider range of
hazardous area sounders, beacons and combination units
.
Available colours depend on the product technology and ordered configuration. The examples below illustrate three different signalling ranges.
Steady visual signalling options include clear, red, blue, green, yellow and amber lens configurations, depending on the selected model.
Available signal colours include white, red, yellow or amber, green and blue, with transparent or coloured cap options depending on the configuration.
Xenon-strobe cap colours include transparent, red, amber, green and blue for the 5J and 15J product options.
Confirm colour availability against the current product datasheet and complete ordering code. Not every colour is available for every voltage, signal mode or approval.
Colour selection should take place after the hazardous area and technical requirements have been established.
For the complete product-selection process, read
How to Select an ATEX Beacon
.
Include the following information when requesting a quotation:
No. Red commonly indicates danger or emergency, but its exact meaning must be defined by the site alarm philosophy. Some sites reserve red specifically for fire or evacuation.
They are frequently grouped as caution or warning colours, but manufacturer terminology and exact optical characteristics can differ. Use the stated ordering colour and code.
It can, but not automatically. Clear describes the lens or cap, while white describes the emitted light. Check the light source and product configuration.
Yes. Lens filtering and LED wavelength can affect the measured and apparent output. Check the manufacturer’s data for the exact colour.
Yes, but personnel must still be able to distinguish the intended conditions. Similar patterns and poor colour contrast can create confusion.
No. Zone suitability is determined by the complete certification and equipment marking. Lens colour affects the visual signal but does not establish the hazardous area classification.
Send Thorne & Derrick the hazardous area classification, intended alarm meaning, signal mode, viewing conditions, voltage and required colour for product selection support.
Explore red, amber, green, blue and clear visual signalling options with LED, xenon, steady, flashing and rotating configurations.
Steady, flashing, strobe and rotating beacons communicate different types of warning and status information. Although each produces a visible signal, the way that signal attracts attention and conveys meaning can vary considerably.
A steady beacon provides continuous illumination. A flashing beacon switches between illuminated and non-illuminated states. A strobe beacon produces brief, high-intensity pulses, while a rotating beacon creates the appearance of a moving light.
Thorne & Derrick supplies a comprehensive range of hazardous area ATEX beacons with steady, blinking, strobe, xenon-flash and electronically rotating visual signals.
For an introduction to hazardous area visual signalling, read What Is an ATEX Beacon?
Quick answer: use steady illumination for persistent status indication, flashing or strobe signals where increased attention is required, and rotating signals where a distinctive moving visual warning supports the site alarm philosophy.
| Signal Mode | Visual Behaviour | Typical Purpose | Important Selection Data |
|---|---|---|---|
| Steady | Continuous illumination | Persistent equipment, plant or process status | Optical output, colour, viewing distance and continuous-duty rating |
| Flashing or Blinking | Repeating on-and-off pattern | Warning, changing condition or attention signal | Flash frequency, duty cycle, colour and control method |
| Strobe | Brief, rapid or high-intensity pulses | Prominent alarm or emergency warning | Flash energy or optical intensity, frequency and current consumption |
| Rotating | Moving beam or electronically sequenced segments | Distinctive warning or recognisable plant-status signal | Rotation rate, field of view, mechanism and maintenance requirements |
Important: the most attention-grabbing signal is not automatically the correct choice. The selected mode must agree with the site alarm philosophy and remain distinguishable from other alarms and equipment-status indicators.
A steady beacon remains illuminated while the electrical supply or control signal is present. It provides a continuous reference rather than repeatedly attracting attention through movement or flashing.
This makes steady signalling particularly useful for showing a persistent operating state or condition.
Continuous illumination may attract less immediate attention than a changing or moving signal. A steady beacon can also become part of the visual background where several continuously illuminated indicators are present.
Viewing distance, mounting position, lens colour and contrast against the surrounding environment should therefore be assessed.
A flashing or blinking beacon changes between illuminated and non-illuminated states at a defined frequency. The changing light level can attract more attention than a steady signal.
In many LED products, the pattern is produced electronically. The flash rate may be fixed or selected from the modes available within the product.
Flash frequency describes how often the signal repeats. The correct frequency should be determined by the product capability and site alarm philosophy.
Two alarms with similar colours and flash frequencies may be difficult to distinguish. Signal patterns should therefore be coordinated across the installation.
“Flashing” is a broad description for a light that repeatedly switches on and off. A strobe is a more specific type of flashing signal that produces brief and often high-intensity pulses.
A xenon strobe discharges stored electrical energy through a xenon flash tube. Its output is commonly specified using flash energy in joules and flash frequency.
An LED strobe creates its pulse electronically. Its optical performance is not automatically equivalent to a xenon flash with a stated joule rating.
| Comparison | LED Strobe | Xenon Strobe |
|---|---|---|
| Light source | Light-emitting diodes | Xenon flash tube |
| Signal generation | Electronically controlled LED pulses | Discharge of stored electrical energy |
| Common performance data | Optical intensity, pattern and pulse frequency | Flash energy in joules and flash frequency |
For a fuller technology comparison, read LED vs Xenon ATEX Beacons.
A rotating beacon creates a moving visual signal that appears to sweep around the installation. This movement can make the signal recognisable even where several fixed lights are present.
Rotating signals can be produced mechanically or electronically.
A mechanically rotating design uses a motor and rotating reflector or light assembly to direct the beam around the beacon.
Rotation speed, motor life and moving-part maintenance should be considered when specifying this type of product.
An electronically rotating beacon illuminates LED segments in sequence. This creates the appearance of movement without a motor-driven reflector.
Different electronic rotation patterns or speeds may be available, depending on the model.
No single signal mode is the most visible under every condition. Visibility depends on the product output, signal pattern and installation environment.
Consider:
The product should be positioned so that the intended audience can see and interpret the signal from the required working locations.
A signal mode does not automatically carry one universal meaning across every site. Its purpose should be defined within the alarm philosophy, operating procedure or project specification.
For example, one installation may use steady illumination for normal equipment status and flashing red for an alarm. Another site may reserve flashing signals for evacuation and use rotating amber for machinery movement.
The meaning must therefore be documented, communicated to personnel and applied consistently.
Lens or LED colour helps distinguish between alarm and status conditions, but it can also affect the apparent optical output.
The visibility of red, amber, green, blue, yellow or clear signals can differ according to the light source, lens construction and surrounding lighting.
Manufacturer performance data should be checked for the exact ordered colour.
Signal mode can affect the beacon’s current consumption and control requirements. The exact electrical data should be checked for the selected voltage, colour and operating pattern.
Confirm:
Check the ordered variant: a product family may offer several modes, but this does not necessarily mean that every configuration can change modes remotely while in service.
The visual signal alone does not determine whether a beacon is suitable for an explosive atmosphere. The complete certified construction and equipment marking must match the installation.
Check:
Read more about ATEX and IECEx certification of hazardous area equipment.
The installation zone should also be confirmed using the guide tohazardous area zones and explosive atmosphere classification.
These products illustrate different signal behaviours. The complete technical and certification requirements must still be checked for each application.
The MEDC FB11 filament and FL11 fluorescent units provide steady illumination for persistent warning or status indication.
The Eaton FHF dSLB20 LED provides steady, blinking, strobe and electronically rotating operating patterns.
The Eaton FHF dSLB20 xenon version provides 5J and 15J strobe options with an approximate frequency of 60 flashes per minute.
Selection should begin with the hazardous area and site alarm requirements rather than a preference for the most visually dramatic product.
| Requirement | Signal to Consider | Reason |
|---|---|---|
| Persistent equipment or process state | Steady | Provides continuous status indication |
| Abnormal condition requiring attention | Flashing or Blinking | Changing signal can attract attention |
| Defined high-intensity pulsed warning | Strobe | Produces brief and distinctive visual pulses |
| Recognisable moving visual signal | Rotating | Creates an identifiable sweeping or sequenced effect |
For the complete selection process, including zone, certification, temperature, voltage and environmental conditions, read How to Select an ATEX Beacon.
A beacon may form only one part of the alarm arrangement. Audible and visual signals are often combined where personnel may not always be looking towards the beacon or where high noise, hearing protection or visibility restrictions affect alarm recognition.
The alarm design should establish whether a beacon, sounder or combined unit is required.
Explore the wider range of hazardous area sounders, beacons and combination units.
A changing signal can attract more attention, but actual visibility depends on optical output, viewing distance, colour, ambient lighting, mounting position and surrounding visual conditions.
A strobe is a type of flashing signal characterised by brief pulses. The term flashing can also describe slower or less intense on-and-off patterns.
Normally, no. Electronically rotating products create the effect by illuminating LED segments in sequence rather than using a motor-driven reflector.
Some LED products provide several internally selectable modes. Confirm whether the selected variant supports the required patterns and whether they are chosen during installation or controlled remotely.
Steady illumination is commonly suited to persistent status indication. Flashing or rotating modes may be more appropriate where the condition needs to attract immediate attention.
No. Zone suitability is determined by the complete equipment certification and marking, not by whether the visual signal is steady, flashing or rotating.
Send Thorne & Derrick the hazardous area classification, required alarm behaviour, viewing conditions, voltage, colour and installation environment for product selection support.
Explore steady, flashing, strobe and rotating signalling devices for Zone 1, Zone 2, Zone 21 and Zone 22 installations.
Published 13 Mar 2020
Press Release Date: 02.04.2020 uploaded by Chris Dodds (T&D Sales + Marketing Manager) World’s First Fully Certified ATEX Doors Thorne & Derrick International, the Experts in Equipment for Explosive Atmospheres, today announce the signing of a Commercial Distribution Agreement...
Published 04 Jul 2019
Press Release Date: 04.07.2019 uploaded by Chris Dodds (T&D Sales + Marketing Manager) Category: Stockist Distributor Agreement Announcement Thorne & Derrick International announce that they have signed a Preferred Distributor Agreement with Raytec, the world leading manufacturer of LED...
