Recently, we discovered online a page dedicated to dry ice cleaning at gas stations. Dry ice blasting in ATEX zones, particularly at service stations, is a delicate operation that requires specific precautions. This process, which uses Carbon dioxide ice projected at high speed, generates static electricity that can cause explosions in the presence of fuel vapors or flammable gases.
This article details the risks associated with using dry ice blasting in ATEX zones and proposes solutions to ensure safe intervention.
Why does dry ice blasting generate static electricity?
Le cryogenic cleaning relies on the projection of Carbon dioxide ice which (changes from solid state to gas state), leaving on the ground only (transition from solid to gaseous state) upon contact with the surface. This process, combined with friction waste, particles of CO₂ and the exact nature of the cleaned materials, generates static electricity. In a dry environment such as a service station, this static electricity is less effectively dissipated, increasing the risk of electrostatic discharge.
Several factors contribute to this generation of static electricity:
- Mechanical friction: the contact between CO₂ particles and the surface creates electron transfer and static electricity accumulation.
- Insulating materials: surfaces made of plastic or insulating materials accumulate more electrostatic charges.
- Dry environment: the dry air at service stations limits static electricity dissipation.
ATEX zones at a service station: classification of risk areas
Service stations contain different ATEX zones classified according to the probability and duration of explosive atmospheres:
- Zone 0: Explosive atmosphere present permanently (e.g., inside fuel tanks).
- Zone 1: Explosive atmosphere likely to form occasionally (e.g., around fuel pumps).
- Zone 2: Explosive atmosphere present very occasionally and for a short duration (e.g., near pumps)
Dry ice blasting in ATEX zones: risks and solutions
The main risk of cryogenic cleaning in ATEX zones is ignition of waste, fuel vapors by an electrostatic discharge. To minimize this risk, two main solutions are available to professionals:
1. ATEX-certified equipment
The use of ATEX-certified equipment is essential for working in ATEX zones. These devices are designed to limit static electricity accumulation and discharge. They incorporate notably:
- Grounding: to evacuate electrostatic charges.
- Antistatic systems: to minimize static electricity generation.
- Spark-resistant materials: To prevent spark formation in case of impact or friction.
2. Temporary zone downclassification
Temporary downclassification of an ATEX zone before dry ice blasting is another option. This procedure involves:
- Ventilation: Eliminating flammable vapors through adequate ventilation.
- Neutralization of ignition sources: turning off electrical equipment and running motors.
- Atmospheric monitoring: using flammable gas detectors.
Concrete example: dry ice blasting at a service station
Let's take the concrete example of a service station:
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Zone 1 (around pumps): Since the risk of explosive atmosphere is present, dry ice blasting can be performed, but only with ATEX-certified equipment. This specific equipment incorporates antistatic devices and grounding to prevent any electrostatic charge accumulation. Furthermore, adequate ventilation is essential to disperse fuel vapors and minimize the risk of ignition.
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Zone 2 (adjacent areas): In this area where the risk is lower, temporary downclassification is feasible. Before proceeding with cleaning, you must ensure that all potential ignition sources are eliminated (turn off electrical equipment, motors, etc.) and ventilate the area to evacuate flammable vapors. Continuous atmospheric monitoring using gas detectors is also recommended to ensure the safety of the operation.
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Zone 0 (inside tanks): Due to the permanent presence of an explosive atmosphere, dry ice blasting is strongly discouraged inside tanks. Other cleaning methods, specific to this type of zone, should be prioritized.
Dry ice blasting in ATEX zones is an effective solution, but it is crucial to comply with safety standards and to use appropriate equipment or temporarily downclassify the zone (the most sensible option). A rigorous risk assessment is essential to ensure the safety of operations.
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