ISA 60079-28

This standard explains the potential ignition hazard fromequipment using optical radiation intended for use in explosive gasand combustible dust atmospheres. It covers EPLs Ma, Mb, Ga, Gb,Gc, Da, Db and Dc. It also covers equipment, which itself islocated outside but its emitted optical radiation enters suchatmospheres. It describes precautions and requirements to be takenwhen using optical radiation transmitting equipment in explosivegas and combustible dust atmospheres. It also outlines atest method, which can be used to verify a beam is not ignitioncapable under selected test conditions, if the optical limit valuescannot be guaranteed by assessment or beam strengthmeasurement.

This standard contains requirements for optical radiation in thewavelength range from 380 nm to 10 μm. It covers the followingignition mechanisms:

• optical radiation is absorbed by surfaces or par ticles,causing them to heat up and, under certain circumstances, this mayallow them to attain a temperature which will ignite a surroundingexplosive atmosphere;

• direct laser induced breakdown of the gas at the focus of astrong beam, producing plasma and a shock wave both eventuallyacting as the ignition source. These processes can be supported bya solid material close to the breakdown point.

NOTE 1 See items a) and d) of the introduction.

This standard applies to optical fibre equipment and opticalequipment, including LED and laser equipment, other than asdetailed below:

• Non-array indicator LEDs used for example to show equipmentstuatus or backlight function.

• Luminaries involving light sources as follows.

– LED light sources for Gc and Dc applications.

– light sources, other than LED, that are continuous anddivergent for all EPL applications.

• Optical radiation source for Gc and Dc applications whichcomply with Class I limits in accordance with us Code of FederalRegulations, 21 CFR Part 1040.

• Optical radiation sources for Mb, Gb or Gc, and Db or Dcapplications which comply with Class 1 limits in accordance withIEC 60825-1.

NOTE 2 Class I limit evaluations in accordance with US Code ofFederal Regulations, 21 CFR Part 1040 are based on normal operatingconditions. Class 1 limit evaluations in accordance with IEC60825-1 are based on normal operating and single faultconditions.

This standard does not cover ignition by ultraviolet radiationand by absorption of the radiation in the explosive mixture itself.Explosive absorbers or absorbers that contain their own oxidizer aswell as catalytic absorbers are also outside the scope of thisstandard.

This standard specifies requirements for equipment intended foruse under atmospheric conditions.

This standard supplements and modifies the general requirementsof ANSI/ISA-IEC 60079-0. Where a requirement of this standardconflicts with a requirement of ANSI/ISA 60079-0, the requirementof this standard will take precedence.

NOTE  Although one should be aware of ignition mechanism b)and c) explained in the introduction, they are not addressed inthis standard due to the very special situation with ultravioletradiation and with the absorption properties of most gases (seeAnnex B).

NOTE Safety requirements to reduce human exposure hazardsfrom fibre optic communication systems are found in IEC60825-2.

Edition:

1.1

Published:

08/21/2013

ANSI:

ANSI Approved

Number of Pages:

52

File Size:

1 file , 890 KB