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Prenormative research on the use of optics in potentially explosive atmospheres

Objective



Background
Optical sensors and communications networks in hazardous
plants are increasingly replacing their electrically
operated equivalents. Optical sensors are unaffected by
electrical or magnetic interference and are inherently
safer in hazardous atmospheres; however, safety factors
will impose limitations on transmitted optical power or
energy. A previous project, also EC-supported,
investigated the use of optical methods of measurement in
potentially explosive atmospheres and defined the most
likely hazard as light falling on dust or fibres and
causing a local temperature rise. That project resulted
in a recommendation for safe levels of continuous optical
power for even the most easily ignited gases.

Objectives
The current project is investigating the safe use of
optical methods of measurement and communication in
industry, particularly where explosive atmospheres may be
present. It extends the previous study to include pulsed
optical sources and also address the change in hazard
presented (by pulsed or continuous optical sources) when
the dust is itself is combustible. Safe optical powers
or energies for industrially important hazardous gases,
solvents and dusts will also be investigated. The project
is expected to result in recommendations for safe optical
power and energy levels for inclusion in standards,
leading in due course to safer operating procedures.

Work programme
Task 1: Explosion initiation by pulsed light sources
The safe levels of pulsed optical energy permissible in
various gases and dust clouds will be determined, as a
function of pulse duration, repetition rate and number of
repetitions.
Task 2: Explosion initiation by optical irradiation of
combustible particles
The objective is to determine safe levels of optical
power, power density or energy when the optical beam,
pulsed or continuous, is illuminating combustible or
active dust particles.
Task 3: Variation of explosive atmospheres
Using pulsed and continuous radiation, safe levels of
optical power or energy in industrially important gases
and vapours, such as the hydrocarbons and solvents, will
be investigated.
Task 4: Input to standards and directives
The data generated during the project, and other relevant
information, will form the basis for a recommendation on
safe power and energy levels. This will be provided to
the standards committees CEN TC305, TC 114 and CENELEC
TC31 in suitable form for incorporation into standards
and directives for safe equipment or particles in
potentially explosive atmospheres, including ATEX 100a
and prEN1127-1.

State of progress
The project proceeded according to plan during the first
six months. For Task 2, the materials initially chosen
for investigation were: iron oxide (non-rust), iron rust,
coal, soot and an inert material (Kaowool). For Task 3
the selected gases were: acetylene, ethylene, heptane,
ethanol, propanol, propane, butanol and mixtures of
heptane-ethane and hydrogen-methane. Dusts chosen include
starch, sulphur and lycopodium. Industry and standards
organisations have been invited, by means of a publicity
campaign, to put forward their views on further gases,
dusts and materials which are of particular importance to
industry.

Coordinator

IMPERIAL COLLEGE OF SCIENCE, TECHNOLOGY AND MEDICINE
Address
Prince Consort Road
SW7 2AZ London
United Kingdom

Participants (3)

Bundesrepublik Deutschland
Germany
Address
100,Bundesallee
38116 Braunschweig
Health and Safety Executive (HSE)
United Kingdom
Address
Broad Lane
S3 7HQ Sheffield
Institut National de l'Environnement Industriel et des Risques
France
Address
Parc Technologique Alata
60550 Verneuil-en-halatte