ISA 60079-28

This standard  explains the potential ignitionhazard from equipment using optical radiation intended for use inexplosive gas atmospheres. It also covers equipment, which itselfis located outside but its emitted optical radiation enters suchatmospheres. It describes precautions and requirements to be takenwhen using optical radiation transmitting equipment in explosivegas atmospheres. It also outlines a test method, which can be usedto verify a beam is not ignition capable under selected testconditions, if the optical limit values cannot be guaranteed byassessment or beam strength measurement.

NOTE 1 Throughout this standard, reference is made toequipment protection levels (EPLs) as a means to determine theapplicability of requirements (see ISA 60079-0 for the definitionof EPLs). While NFPA 70 (NEC) does not preclude marking of theequipment protection level (EPL), the concept of a risk assessmentto establish the selection of equipment for specific areas based onthe assigned EPL for the specific area is not currently recognized.Therefore, when applying this standard, the EPL designations shownare to be understood as meaning equipment.

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 21 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 to show equipment status (suchas standard pan el-mount indicator LEDs).

• Luminaires with divergent light sources.

• Optical radiation sources for Gc applications which complywith Class I limits in accordance with US Code of FederalRegulations, 21 CFR Part 1040.

• Optical radiation sources for Gb or Gc applications whichcomply with Class 1 limits in accordance with IEC 60825-1.

NOTE 3 Class I limit evaluations in accordance with US Codeof Federal Regulations, 21 CFR Part 1040 are based on normaloperating conditions. Class 1 limit evaluations in accordance withIEC 60825-1 are based on normal operat ing 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– 60079-0. Where a requirement of this standardconflicts with a requirement of ANSI/ISA– 60079-0, therequirement of 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.

NOTE Safety requirements to reduce human exposure hazards fromfibre optic communication systems are found in IEC 60825-2:

NOTE Types of protection “op is”, “op pr”, and “op sh” canprovide equipment protection levels (EPL) Ga, Gb, or Gc. Forfurther information.

Edition:

12

Published:

12/05/2012

ANSI:

ANSI Approved

Number of Pages:

52

File Size:

1 file , 630 KB