1、 Explosion proof design analysis: essential safety guarantee from structure to function
Portable total hydrocarbon analyzerThe explosion-proof design must meet the explosion-proof (Ex d) or intrinsic safety (Ex ia) standards, with the core being to block the synergistic effect of the three elements of combustion (combustibles, oxygen, ignition source) through physical isolation, energy limitation, and material selection.
Explosion proof shell design
Material and Structure: The shell is made of high-strength stainless steel or aluminum alloy, with a thickness of ≥ 3mm and a joint surface gap of ≤ 0.15mm, ensuring that the internal explosive energy cannot be transmitted to the external environment. For example, the explosion-proof chamber of a certain model of analyzer adopts double protection of hollow cylindrical joint surface and explosion-proof thread, which can withstand 1.5 times the maximum explosion pressure.
Sealing: All interfaces (such as gas, power, and data interfaces) are designed with double-layer sealing rings, with an IP66 protection level to prevent dust and water from entering and prevent external combustible gases from infiltrating the instrument.
Intrinsic safety circuit
Energy limitation: By using current limiting resistors, voltage stabilizing diodes, and other components, the voltage, current, and energy in the circuit are limited within a safe range. For example, the output voltage of the hydrogen detection module is ≤ 12V and the current is ≤ 100mA, which is much lower than the minimum ignition energy of hydrogen (0.02mJ).
Explosion proof components: Intrinsically safe sensors and circuit boards that comply with GB 3836.4 standards are used, with a surface temperature of ≤ 85 ℃ to avoid high temperature ignition of flammable gases.
Explosion proof certification and labeling
The instrument needs to be certified by ATEX (European Union), IECEx (International) or CNEx (China), and the explosion-proof mark (such as Ex d ia IIC T4 Gb) should be marked on the shell, clearly indicating the applicable gas group (Class II) and temperature group (T4 level, maximum surface temperature 135 ℃).
2、 Taboos for operating in hazardous environments: Avoiding three high-risk scenarios
When using portable total hydrocarbon analyzers in flammable and explosive places such as petrochemicals and pharmaceuticals, the following taboos must be strictly followed to avoid explosion accidents caused by improper operation.
Taboo scenario 1: Power on directly without gas replacement
Risk: If there is residual combustible gas (such as methane) inside the instrument, the high-voltage circuit may generate electric sparks when turned on, igniting the gas.
Standardized operation:
Before starting up, blow the internal gas path of the instrument with nitrogen gas (flow rate ≥ 500mL/min, time ≥ 5 minutes) to ensure that the residual gas concentration is below 25% of the lower explosive limit (LEL).
Example: Before testing in the catalytic cracking unit area of a refinery, the sampling pump needs to be turned off and the gas bag and pipeline need to be replaced with nitrogen three times.
Taboo scenario 2: Using non explosion proof accessories in oxygen rich environments
Risk: An oxygen rich environment (oxygen concentration>23.5%) can significantly reduce the lower explosive limit of combustible gases, and non explosion proof sampling pumps or data cables may become ignition sources.
Standardized operation:
Only use explosion-proof certified accessories (such as explosion-proof sampling pumps, intrinsic safety data cables), and avoid using ordinary rubber pipes or plastic joints.
Case: A chemical plant experienced an explosion when an oxygen pipeline leaked due to the use of a non explosion proof sampling pump, resulting in casualties.
Taboo scenario 3: Failure to cut off power, replace battery or charge
Risk: Electrified operations in explosive gas environments may generate arcs and ignite gases.
Standardized operation:
Before replacing or charging the battery, move the instrument to a safe area (such as a fume hood or outdoors) and turn off the power switch.
When charging, use an explosion-proof charger to avoid overcharging (voltage ≤ 12.6V) or overdischarging (voltage ≥ 10.8V).
3、 Safe usage process: full chain control from preparation to closure
Check before use
Confirm that the explosion-proof label of the instrument matches the gas group on site (e.g. Ex d ia IIC is suitable for environments such as hydrogen and ethylene).
Check if the air circuit connection is secure and test the interface for leaks using soapy water (leakage rate ≤ 1 × 10 ⁻⁶ Pa · m ³/s).
Key points of on-site operation
During sampling, keep the probe perpendicular to the discharge port to prevent gas from flowing back into the instrument.
If the concentration of combustible gas is detected to be close to 50% of LEL, immediately stop the detection and evacuate the scene.
Post use maintenance
Blow the gas path and sensor with nitrogen to avoid residual corrosion of components.
Keep the storage environment dry (relative humidity ≤ 75%), temperature -20 ℃~50 ℃, and avoid direct sunlight.
4Portable total hydrocarbon analyzerEmergency response: rapid response to fires and leaks
Fire: cut off the power immediately, put out the initial fire with dry powder extinguisher, and prohibit water or foam extinguisher.
Gas leakage: Quickly close the gas source valve, open the ventilation system, evacuate personnel to the upwind safe area, and set up a warning line.