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Portable Safety Lighting

Published: 01st Apr 2008

ARTICLE CONTINUES BELOW

ATEX safety lighting and LED technology

Portable safety lighting for use in explosive atmospheres has undergone many changes in recent years. Design standards have been subject to regular review and update, the ATEX Directives have been introduced; combined, these have brought about more onerous design and manufacturing requirements and greater standards of safety. Technology is moving at a pace, the development of battery, electronic control and LED technology offering real benefits to users.

Hazardous areas

‘EX’ hazardous areas are where explosion and fire hazards can be found, caused by potentially explosive gas, vapour, mist or dust atmospheres. Hazardous areas occur in many industries, including petrochemical, marine, distilling, offshore, aviation and the utilities. They are most likely to be found in areas where flammable materials are stored or used in manufacturing or power generation, and in enclosed or partially enclosed spaces, such as process vessels, storage tanks, warehouses, culverts, sewers, tunnels and shafts.

Explosion risk

Explosion occurs when all the elements of the fire triangle are present; the ‘fuel’, oxygen to support combustion, and the ignition source.

The fuel will be a potentially explosive gas, vapour, mist or dust. Fuels can range from the obvious: propane from gas cylinders, and the ‘everyday’: petroleum vapour, to the apparently innocuous: baking flour or aluminium powder. The fuel needs to be mixed with oxygen, most likely in the form of air, and be airborne and in the correct ratios to be within the ‘explosive limit’. Finally the ignition source must have sufficient energy to cause combustion resulting in fire or explosion. Ignition sources include open flames, exposure to hot surfaces, high temperatures, friction, mechanical impact, electrical sparks, and electrostatic discharge.

Explosion results in uncontrolled flame and pressure effects in the form of heat radiation, flames, pressure waves and flying debris, and from the harmful products and the depletion of the breathable oxygen in the ambient air. Injuries sustained by workers can be fatal; damage caused to plant can be catastrophic.

If one of the three elements of the fire triangle is eliminated, combustion cannot occur. ATEX compliant electrical apparatus is used in explosive atmospheres because the design mitigates, or completely eliminates, the risk that such equipment will become an ignition source.

With ‘ATEX’ lighting equipment the major ignition risks considered in design and approval are:

  • High temperatures (lamps/light sources, battery packs and electronic components in short circuit fault conditions)
  • High-energy incentive sparks (battery pack short circuits and circuit faults)
  • Electrostatic hazards (from the enclosure)

Hazardous areas and legislation

The 99/92/EC (ATEX Workplace) Directive covers the “minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres”. The Directive lists a set of legal obligations for employers, requiring a risk assessment based strategy for the prevention of explosions and fire. All workplaces within the EU where explosive atmospheres may be found are required to comply with this Directive. In the UK the 99/92/EC Directive has been implemented as the Dangerous Substances and Explosive Atmosphere Regulations 2002 (DSEAR). These regulations also include the fire safety aspects of the 98/24/EC Chemical Agents (CAD) Directive.

The 94/9/EC (ATEX Equipment) Directive deals with “equipment and protective systems intended for use in potentially explosive atmospheres”. Only ‘ATEX’ equipment CE marked compliant with this Directive may be sold within the EU for use in applications where potentially explosive atmospheres may be found.

ATEX requires that all equipment for use in explosive atmospheres must be risk assessed for safe use, to include:

  • Confirmation that equipment has an approval for use in explosive atmospheres (ATEX approval for newer equipment, existing ‘Ex’ equipment may continue to be used)
  • Verification that equipment is appropriate for use in the explosive atmospheres to be encountered (temperature class, gas group, hazardous area zones)
  • Consideration of where mobile or portable work equipment is used (zones, temperature classes or gas groups)
  • Environmental conditions the equipment will encounter (resistance to water, dust, chemical attack, impact and harsh conditions, etc.)
  • Confirmation that equipment is operated and maintained with due regard to safety

ATEX lighting selection

A wide variety of ‘ATEX’ explosion-protected lighting is available. To ensure safe use, the correct selection criteria are critical:

  • Characteristics of the explosive atmosphere (temperature class, gas group, zone)
  • Amount and type of light required for task
  • Task duration
  • Conditions (e.g. wet, harsh)

ATEX portable lighting and new technology

Technological advances - batteries and control circuits

Rechargeable battery technology has made great advances in recent years. Lithium Ion (Li-Ion) rechargeable battery chemistry has emerged as the battery technology of choice for high-end electronic equipment from cell phones to laptop computers. Li-Ion cells coupled with sophisticated electronic controls now being utilised in rechargeable ATEX torches to maximise functionality and user benefit; key advantages include:

  • Very high power density with low weight
  • Environmentally friendly
  • Low self-discharge and no memory effect
  • Fast charge rate
  • Battery status indication
  • Multifunction light output modes (high/low power, flash mode)

Only where significantly greater levels of light output and operational duration are required does Li-Ion battery technology fail to deliver. Products, such as self-contained battery powered work lights, fall back on high capacity Lead Acid technology.

Technological advances - LEDs

The greatest technological advance in recent years for portable lighting for use in potentially explosive atmospheres has been the LED.

What are LEDs?

LEDs or light-emitting diodes are solid state semiconductor devices, essentially electronic components. When energised they emit narrow-spectrum light, in the form of electroluminescence, an opto-electrical phenomenon where a material emits light in response to an electric current passed through it.

Background - LEDs

LEDs were first commercialised in the 1970s as indicators and in digital displays. Nichia demonstrated the first high-brightness blue LED in 1996, which led quickly to the first white LED. LEDs have seen greater and greater use in portable lighting over the last 10 years. White LEDs were originally restricted to low power devices. It was not until the development of the high-power 1-watt LED in 2000 that a serious contender to the filament lamp emerged.

White LEDs

The majority of “white” LEDs in production today are modified blue LEDs covered with a yellow phosphor coating. The emitted blue light ‘excites’ the yellow phosphor, converting to a broad spectrum ‘white’ light source. Since yellow light stimulates the red and green receptors of the human eye, the resulting mix of blue and yellow light gives the appearance of ‘cool’ white.

Advantages of LEDs

  • Efficiency - LEDs produce more light per watt than incandescent bulbs; Halogen torch bulbs typically deliver 10 to 15 lumens per watt, LEDs applied in torches are now delivering 25 to 40 lumens per watt. This is a significant advantage in battery devices where power is limited but light output and duration are so important
  • Robustness - LED ‘solid state’ technology offers an inherently robust construction with a greater resistance to the external shock and rough use expected from harsh environments. By comparison, incandescent lamps use a comparatively fragile tungsten filament light source, susceptible to fracture from knocks or drops
  • Long life - LED manufacturers suggest a single device can give 50,000 hours of light (5 continuous years of use). LED light sources are ‘fitted for life’ and should more than last the life of a torch, requiring zero maintenance. The typical life of a torch filament bulb is 20-30 hours
  • Failure - The most common way for LEDs to fail is the gradual dimming of light emitted, rather than the abrupt burn-out of filament bulbs
  • Optics - LEDs give an excellent, controlled light, which is considerably whiter than halogen bulbs. Portable lighting manufacturers are starting to develop products with bespoke LED optics, some offering very impressive solutions with smooth, even beams. Good LED optical solutions can offer excellent beams without the shadows, rings and black holes caused by the jagged filaments in incandescent bulbs
  • Output characteristics - LEDs are more robust over variances in supply power. LEDs have a relatively linear relationship between current supplied and light emitted; if power drops by a set percentage, light will drop by a comparable amount and light colour will not significantly change. By comparison incandescent lamps are very sensitive to changes in the supply power. Typically, a 5% reduction in operating power will reduce light output by about 20%, additionally light ‘colour temperature’ will drop significantly from white to yellow
  • ATEX equipment benefits - LEDs offer real advantages for portable hazardous area equipment. They are a ‘cool’ solid-state technology; they do not present the hazards of hot filaments in incandescent lamps, but lend themselves to higher levels of protection with the opportunity of use in category 1 equipment for Zone 0

Disadvantages of LEDs

  • Cost - LED torches and portable lighting are generally found to be more expensive than comparable incandescent products. The technological requirements of the LED require electronic control and strict thermal management, necessitating the incorporation of heat sinks to ensure reliability. For critical applications users are now able to justify purchase based on total life time cost, in such cases LED products with a higher initial purchase cost can be shown to have a lower ‘cost of ownership’ than those fitted with incandescent bulbs

ATEX lighting showcase - LED lights in use in industry

Recent developments in lighting technology are pushing the boundaries of safe lighting technologies to give a safe yet far more useable light.

In the past, to be safe a lamp’s performance was limited by the fact that certain technologies were not permitted - for example halogen filled filament lamps - because of the high temperatures at the source of the light, and high energy dense alkaline cells, which could not be used for fear of short circuit that would produce enough heat to ignite a gas and thus cause an explosion.

Continuing development of high power LEDs, rechargeable and primary cell battery technologies, as well as a review of the criteria for certification used in the European market, notably the ATEX equipment directive, have lead to more powerful light sources that are safer than those used in the past. As a result this has led to a consumer driven demand for more powerful lighting that is approved for safe use in more dangerous environments.

By using portable rechargeable LED based floodlights designed around shift work durations, a leading hire company with contracts in the UK offshore industry for blasting, cleaning, maintaining and painting oil storage tanks is finding that they are having trouble keeping up with the demand for their services. The approach of using “task oriented” lighting where the operator can move the light to suit their requirement, is a much more flexible method than a lighting solution involving lamps and transformers, which can cause potential trip hazards, trapped and chopped cables, as well as much longer setup times.

The major benefit is the increased level of light output from the high-power LED light sources, the latest high power LEDs operate at a level now approaching the efficiency of fluorescent lighting. Normal incandescent light bulbs produce 15-20 lumens per watt; modern fluorescent bulbs produce between 60-110 lumens per watt; and current LED methods allow for a maximum of 60-70 lumens per watt. Research into LEDs is now at an all time high with the efficiency of LEDs expected to reach 200 lumens per watt in the next 5 years. (source: www.treehugger.com/files/2005/11/white_led_break.php)

The advantage of LEDs compared with incandescent and fluorescent light sources is a much brighter and focusable light which, when combined with the right optics, produces a far more useable light. In the pictures shown previously on page 94 there are 3 examples of portable, rechargeable safety approved lighting for use in potentially explosive atmospheres in a tunnel 10 metres away from a wall. One based on incandescent bulbs, one on fluorescent lighting and the other on LEDs.

Incandescent light has a yellow light output which causes the light to be absorbed in the darkness, the fluorescent lamp although more efficient does not have the optics to penetrate the darkness for more than a few metres. The led lamp with optics to focus the light into a narrow flood has the ability to penetrate the darkness and illuminates the sides and the end wall 10 metres away.

Developments of the control circuitry in use with rechargeable LED products ensure health & safety protection for the operator and at the same time for the person holding the purse strings. Features such as short circuit protection to prevent sparks or high levels of heat from the short circuit of the recharging contact are standard requirements, but the control circuitry of new generation rechargeable safety lamps also incorporate features like:

  • Deep Discharge Protection to prevent damage to cells in the event of accidentally leaving the torch on for extended periods of time. This gives a much lower maintenance cost of the torch as a reduction in spare batteries is made form the onset as well as extending the life of the initial purchased product
  • The use of Lithium-Ion cells allow the more effective control of charge and discharge cycles leading to an extended life of the product and a lower cost of ownership over the life of the product, allowing the torch to be left on charge for extended periods of time without causing damage to the cells. Fast charge allows the bulk of the charge to be delivered in less time, battery State-of-Charge indication for charge and discharge cycles give the user real time information on the amount of life left in the battery. All this contributes to an easy-maintenance product that will have a lower requirement for spares through the life of the product

Rechargeable torches have now been in use in industries such as the fire service for many years and the true cost of ownership over the life of the product has been hard to judge. With local government budgets being more closely examined, contracts for the supply of potentially life saving equipment are being subject to closer scrutiny. Procurement strategies such as Spend to Save are being used where the whole cost of a product over it’s expected life are examined and the product that is the cheapest does not necessarily have the lowest cost when the amount of spares, replacement batteries and replacement units are taken into consideration

Advances within these products make it much easier to judge the overall cost of product overt time. LED light sources, as long as they are integrated into the product properly, are rated by the manufacturer for 25,000 hours essentially meaning they are ‘Fitted for Life’. Li-ion Battery technology coupled with the correct control circuitry also allows for a constant current to be delivered to the LED light source for a constant level of light output during the battery life prolonging both the life of the LED and the rechargeable cells. All this means that torches that use these types of technology are far more reliable than their counterparts that have no control circuitry.

As LED technology advances it is starting to be used in more cost effective products, and the correct combination of primary cell battery technology with LEDs will provide longer duration as well as a significant increase in light output over similar products using halogen or xenon incandescent bulbs.

For example the latest ATEX Certified TR-40 range of safety torches from Wolf Safety has an impressive 55 lumen output which is more than twice the light output of the TR-24 halogen bulb version which was at the forefront of ATEX Certified technology only 5 years ago. This LED version of the right angle torch for use in Explosive Gas and Dust atmospheres runs for up to 72 hours from 4 AA cells making it more cost effective, lighter weight, and brighter.

Published: 01st Apr 2008 in Health and Safety International

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