1、 Practical application of optical radiation equipment in potentially explosive environments
The invisibility, multiple optical paths, and energy overlap of light radiation propagation have actually caused many safety hazards and even caused many accidents. Therefore, the safety research of optical radiation equipment and transmission systems has become a key focus of its research. In explosive environments, optical equipment is often used in conjunction with electrical equipment. For example, lighting fixtures, lasers, and light-emitting diodes used in communication, surveying, sensing, and measurement activities（LED）Optical equipment such as fiber optics. These devices are typically installed in or near explosive environments, and radiation may pass through explosive environments. Due to the inherent characteristics of radiation, it may ignite explosive environments around it. Additionally, the presence of absorbents can significantly affect ignition. The country has clear explosion-proof testing andExplosion proof certificationStandard regulations. For light radiation equipment used in potentially explosive hazardous environments, the stateGB/T3836.22There are also corresponding explosion-proof technical requirements.
2、 There are four possible mechanisms by which light radiation can ignite:
1. After the surface or particles absorb light radiation, the temperature increases, and under certain conditions, it can reach the temperature required to ignite the surrounding explosive environment
2. When the wavelength matches the absorption band of the gas, a certain amount of combustible gas undergoes hot spot combustion
3. Radiation within the ultraviolet wavelength range causes oxygen molecules to undergo photolysis, resulting in photochemical ignition
4. The laser at the focal point of the strong light beam directly causes gas decomposition, generating plasma and shock waves, which ultimately become ignition sources. Solid materials approaching the decomposition point will exacerbate this process.
What we are talking aboutGB/T3836.22Optical radiation equipment is only applicable to1And the4The wavelength range of the point is380nm-10µmIgnite the possibility.
3、 Three explosion-proof types of optical radiation equipment
Explosion proof electrical optical radiation equipmentopThere are three explosion-proof types available to prevent ignition caused by light radiation in potentially explosive environments. theseExplosion proof typeSuitable for all optical systems.
These three types of explosion-proof protection are:
Intrinsically safe type of optical radiation, explosion-proof type“op is”；
Protective type optical radiation, explosion-proof type“op pr”；
Optical system with interlocking device, explosion-proof type“op sh”；
1Intrinsically safe type of optical radiation, explosion-proof type“op is”
（1）Refers to visible or infrared radiation that does not ignite a specific explosive environment under normal conditions or specified fault conditions. The energy, power, or irradiance in the visible or infrared spectrum that can cause the irradiated body to absorb and ignite is very small, and safety can be achieved by limiting the beam intensity. The principle of intrinsic safety optical radiation is applicable to free radiation, without restricting the presence of absorbers in the environment, and has great flexibility in use.
（2）The optical radiation power or irradiance of different device categories and temperature groups are detailed in the table below
（3）The matching use of intrinsic safety optical radiation equipment
Optical devices that adopt the principle of intrinsic safety should provide fault protection measures when the power/energy exceeds the standard to prevent the occurrence of excessive light radiation in potentially explosive environments. And a hazard/danger analysis should be conducted to determine when these devices are needed. Consider the failure mode of the light source, power isolation, and whether there is an explosive environment to determine whether additional protection is needed. Like laser diodes or light-emitting diodes(LED)If such a light source overheats under power exceeding fault conditions, it will malfunction. The thermal fault characteristics of certain light sources can provide necessary power over limit fault protection measures(10A sample experiment). The circuit with current and/or voltage limiting devices installed between the light source and the power supply can prevent power exceeding faults similar to intrinsic safety circuits.
（4）Protection level of intrinsic safety optical radiation equipment（EPL）
The protection measures for power exceeding the standard fault should be in line with the equipment protection level（EPL）Adapt accordingly. aboutGaGrade equipment, such as current and/or voltage limiting devices, should be able to provide power over limit fault protection after applying two countable faults. For a thousandGbLevel equipment, apply a countable fault. aboutGcGrade equipment should be rated without considering any faults. The thermal fault characteristics of certain low-power light sources, such as light-emitting diodes, can be used for power over limit fault protection of any protection level.
2Protective type optical radiation, explosion-proof type“op pr”
（1）Protective optical radiation requires limiting radiation within optical fibers or other transmission media, and assuming that radiation will not escape from the restricted range. The radiation limitation measures determine the safety level of the system. Conduct hazard analysis based on assumed conditions (fault conditions or normal operation) and propose safety requirements.
（2）Adopting explosion-proof type standards that comply with relevant requirements（GB/T 3836When it comes to the casing of the series, a ignition source is allowed inside the casing, but it cannot ignite the external environment of the casing.
（3）Fiber optic internal radiation: Under normal operating conditions, fiber optic cables can prevent light radiation from escaping into the environment. For foreseeable faults, armor, conduits, cable trays, or cable conduits can be used to provide protection.
（4）Radiation inside the shell: The shell may contain ignition sources if it meets the requirementsGB/T3836The series of standards specifies the requirements for explosion-proof types (explosion-proof enclosures)"d"Positive pressure shell''p"If there are restrictions on the breathing shell, there may be flammable radiation inside the shell. However, radiation escaping from the casing should be protected in accordance with the requirements of this section.
3Optical system with interlocking device, explosion-proof type:“op sh”
（1）If the radiation limitation measures fail and the failure time is less than the ignition delay time, and the radiation becomes a non intrinsic safety state with an interlocking disconnection device, this protection type should be adopted.
（2）The interlocking disconnection device should be activated according to the requirements determined by the hazard analysis. Regarding standards (such asGB/T 20438、GB/T 21109)The prescribed method. Can be used to analyze the safety probability or hazard reduction factor of devices with different protection levels, as shown in the table3As shown.
4、 Applicable standards for explosion-proof certification of optical radiation equipment
1. Domestic standards:GB/T 3836.22-2017Explosive Environment22Part: Protection Measures for Optical Radiation Equipment and Transmission Systems
2. International standards: DIN EN/IEC 60079-28-2015 Explosive atmospheres - Part 28: Protection of equipment and transmission systems using optical radiation
5、 Applicability of Explosion proof Protection Types for Optical Radiation
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