Operating safety lights in potentially explosive atmospheres: Are “Ex” certifications to be trusted?
11 September 2012
Early in April 2012, a third party commissioned DEKRA Certification BV to test six brands of ‘intrinsically safe’ alkaline (4 x AA) powered hand lamps and to validate performance claims published by the different vendors and to verify if the lights were compliant with the issued ATEX certifications.
Elements needed to cause an explosion –the ‘Triangle of Fire’
The results of the study –“Photometric and mechanical testing of six different type of professional torches”*- are a cause of concern leading to the publication of this paper, the scope of which is to explain the basic technical prerequisites which luminaries should fulfil to qualify as ‘Intrinsically Safe’. At the same time, this article will provide operational warnings as, on closer inspection, some luminaries should prove safer than others.
In brief, the DEKRA test report concluded that five out of six flashlight samples did not live up to some of the vendors’ performance claims, for example by overstating lumen ratings, and three samples failed the immersion tests, with water leaking into the battery chamber, in non-compliance with the issued ATEX certifications and IP ratings.
What is Intrinsic Safety?
As pictured below, to cause an explosion three elements must be present: Oxygen, flammable compounds and a spark or a flame. As general definition, equipment termed as ‘Intrinsically Safe’ is incapable to cause electrical sparks or sufficient thermal energy to ignite flammable compounds present in an explosive atmosphere, may they be gases, vapours or dust.
In battery powered luminaries, three main components might cause a spark or a flame:
a) Batteries – they might leak, gas out or short-circuit.
b) Light source – incandescent bulb might break or explode; LED circuits can short-circuit
and components may overheat or become faulty.
c) Enclosure and material - electrostatic discharge can cause sparks.
Gassing alkaline batteries
Handheld flashlights and headlamps require a power source to operate; these can be
rechargeable or non-rechargeable battery cells, e.g. Li-ion, NiMH, NiCd, alkaline, lithium, and so on. Batteries store energy to be released as ‘electrical power’, and depending on chemistry, some batteries are more energetic than others. Yet, batteries may leak over time, gas out or short-circuit damaging the electronics and the enclosure of the luminary. Gassing batteries are of special concern as there are risks that they might explode inside the compartment leading to injuries or, in the worst case, initiating a major explosion. Picture 1 shows an exploded flashlight (with pressure valve) after the inserted alkaline batteries gassed out. Noteworthy is and as the picture shows, ‘safety gas valves’ seem not to offer much protection when batteries start gassing.
As light sources, most handheld flashlights and headlamps use either incandescent bulbs, e.g. Xenon or Krypton, or LEDs. Obviously, light bulbs can burnout or break when lit. Also, light bulbs will become very hot during operation –the brighter the hotter-, heating up the luminary enclosure (and batteries), sometimes to critical temperatures sufficient to ignite flammable gases or dust. Therefore, light bulbs have to pass electrical and the housings mechanical and environmental stress tests before the light will be certified as ‘Intrinsically Safe’.
In case luminaries include an LED light source, it is mostly ignored that LED chips not only generate considerable heat but that they require an electrical circuit and a heat-sink to operate. The Achilles tendon of all LEDs is the electrical circuit, which must be designed and manufactured in accordance with approved safety norms and standards so neither the circuit nor any of its components will short circuit and cause electrical sparks.
Incandescent light bulbs can be directly connected to batteries without having to take polarity into consideration. Therefore, the electrical circuit is rudimentary and consists of a bulb, batteries, contacts and likely a switch.
Exploded lithium batteries
LED emitters are diodes allowing the current to flow in one direction only. In a very simple circuit, LEDs are direct driven, similar to a light bulb. A more expensive option is to drive the LED with a regulated circuitry. But which of the two is more efficient and safer? In terms of performance, the LED with the regulated circuit will fare better than if direct driven; however, electrical safety can only be guaranteed if the regulated circuit includes current limiting resistors, a fuse, and is reverse polarity protected. In addition, all components which might heat up must be insulated, creepage between conductive tracks must be avoided and clean and solid soldering is a prerogative.
Considering the above two circuit types, it is important for the user to know:
a) Direct-driven LEDs are connected directly to the batteries and will be very bright in the first few minutes but then lose rapidly around 50% of the light power! The below graph shows the drastic drop in luminous flux from 96 lumens to 53 lumens within a few minutes (notable is that the DEKRA tested sample is advertised by the vendor to emit “200 lumens”!). For cost considerations and simplicity of engineering, the majority of “intrinsically safe” lights rely on direct driven LED circuits!
b) IC-controlled LED circuits regulate the current supply either by pulse modulation (PWM), constant current (CC) or alternatively by applying constant voltage (CV). In other words, a Microcontroller constantly senses and optimises the forward current respectively forward voltage applied to the LED keeping the light output constant and so reducing negative thermal effects.
IC-controlled LEDs are safer and show a far better performance than direct-driven LEDs.
This graph shows the light performance using a direct-driven LED circuit. Source: DEKRA Certification, Test Sample 2
Enclosures of intrinsically safe lights are predominantly made of plastic, which might have conductive or non-conductive properties. Non-conductive polycarbonate (PC), e.g. Lexan, is the most common and cost effective plastic. Conductive anti-static materials like carbon fibres and “XAG” are expensive and preferred if lights are to be certified for safe use in highly explosive atmospheres. Before a flashlight can be certified as ‘Intrinsically Safe’, the entire enclosure has to pass various laboratory tests which include impact and drop tests, water and dust immersion (IP rating) and, depending on certification, temperature stress and electrical resistivity tests.
IP ratings indicate the level to which the flashlight is water and dust-proof. Water immersion is part of the product certification test programme. After the tests, the product will be IP rated, e.g. IP 67 or IP 68. As an example, IP 67 certifies that the product is dust-proof and suitable for immersion in depths up to one metre. In the mentioned DEKRA report, three out of the six flashlights (50%) failed the one metre immersion test, despite two of the vendors claiming that the affected models are “suitable for diving”!
Norms, Certifications and Inconsistencies
The above comments refer predominantly to ATEX which stands for “Appareils destinés
à être utilisés en ATmosphères EXplosives”; ATEX applies mainly to the European Community (EC). However, countries, such as the US, Canada, Australia, Russia, Japan all implement different Directives –UL, FM, ETL, IECEx, TIIS, to mention a few. It is outside the scope of this paper to explain the nuances and differences of these Directives other than to state that the general product test methods follow and apply schedules similar to ATEX.
In accordance with the various Certification Schemes, ‘Intrinsically Safe’ products can only be distributed if the facilities of certified vendor are audited by a Notified Body (Accredited Organisation). Still, vendors who market “Ex certified” lights under their own brand may not necessarily be the original manufacturer but employ uncertified subcontractors in third countries instead. Many subcontractors do not have any ‘Ex’ Quality Assurance Module in place and the production facilities are not inspected and audited by any Notified Body. In other words, US or European vendors may purchase flashlights either as “Complete Knocked Down” (CKD) kits or as finished products from uncertified subcontractors located in different jurisdictions.
In the case of CKD kits, the vendor assembles the parts at his facilities and sells the products as intrinsically safe lights under his own brand, certified by a Notified Body in his name. So customers purchase, in good faith, a branded and ‘Ex’ certified flashlight or headlamp which might turn out to be unsafe if used in hazardous areas.
This graph shows the light performance with a safe IC-controlled LED circuit Source: DEKRA Certification, Test Sample 1
In the following example, an unnamed European ‘Ex’ safety company markets an alkaline battery- powered headlamp certified to ATEX II 2 G Ex ia T4, - (ia approves the lamp for Gas Zone 0, an area in which explosive gases are continuously present). However, the LED board (pictured below) is made in China by an uncertified subcontractor. The circuit as shown does not include any current limiting resistors or a fuse, components are without insulation and
conductive tracks are closer than permitted, risking current creepage. And yet, the headlamp was approved and certified by a Notified Body in Germany.
Comments on images below:
The headlamp is powered by 2 x AAA batteries (3V).
The light source : 0.5W “two-pin” LED. ATEX Certification: II 2 G Ex ia T4
a) Battery short-circuit current is 5.44A
b) Without fuse and current limiting resistor, the short-circuit across the batteries is calculated to be 27.2W, yet only 0.33W is permitted
c) Inductance is 360µJ, exceeding the permitted 160µJ
See comments above
The aforementioned DEKRA report and the cited examples should sound alarm bells to
users who operate luminaries in hazardous areas. Branded flashlights and headlamps with ‘Ex’ certification are no guarantee that the lights will perform as advertised by vendors and will be truly safe for deployment in potentially explosive atmospheres.
The reasons for this are:
a) Notified Bodies - To be certified as ‘Intrinsically Safe’ , products must comply with specific
norms and standards (e.g. ATEX); nevertheless, it is left to the interpretation of the Notified
Body how to implement these. For safety reasons, and in order to avoid ambiguity, it should be made mandatory that only products can be called and marketed as ‘Intrinsically Safe’ if the
entire production chain, including the main subcontractor who supplies electronic boards and LED modules, is audited and certified by a Notified Body.
b) Certifications Definitions - The various definitions, nomenclature and letterings classifying intrinsically safe products are confusing to most users. As an example, US and European norms refer to “Classes” and “Zones”.
Circuit diagram for product above
c) Vendors - For marketing purposes, some vendors tend to over-emphasise product performance. To be competitive, many ‘Ex’ certified vendors purchase electronics modules, such as complete LED assemblies or even the entire product, from ‘Ex’ uncertified subcontractors, without having any direct control over production, product quality or safety.
d) Users – In a price-driven environment, many customers put a lower priority on safety as long as the product is branded and carries some kind of ‘Ex’ certification. However, users are well advised to select only ‘Ex’ luminaries that are certified by two different organisations, e.g. ATEX and IECEx.
e) Legal Implications - In the event that an ‘Ex’ certified luminary caused an accident, fire or an explosion, the above comments lead to the conclusion that the user will, in the end, bear all responsibilities and liabilities.
And another legal question is: what will happen if a Notified Body has its accreditation
suspended or revoked? Will the products certified by this organisation have their certifications invalidated so that the products cannot be distributed any longer as ‘Intrinsically Safe’ ? The answer remains open!
*Note: DEKRA Certification BV from The Netherlands is an independent internationally accredited Test Institute. The above-mentioned study (DEKRA, Arnheim, 3 April 2012) measured the light performance (luminous flux and intensity, isolux, etc.) and investigated the physical endurance (dust and water ingress, 3 m drop test) of six alkaline (4 x AA) powered handheld torches marketed by different US (3), German (2) and United Kingdom (1) vendors. It should be mentioned that light performance of a torch is not part of intrinsically safe certifications; lumen ratings advertised by vendors are mostly unverified. The circulation of the report remains restricted.
Author: Urs Baeumle, originally from Switzerland, owns and manages Permalight (Asia) Co, Ltd, based in Hong-Kong. The company manufactures a range of professional flashlights and Parat safety lights, which are designed and produced in exclusive co-operation with Parat GmbH of Germany.