11. GENERAL PROCESS INSTRUCTIONS

11.1 Legal basis and regulations (applies in Germany)

The dust generated during the blasting of centrifugal baskets poses both an explosion hazard and a health hazard. The safety parameters for the explosion hazard are described in VDI 2263 Sheet 1. For particle sizes below 500μm, a dust explosion hazard must always be assumed. A median value below 63 μm indicates a high proportion of fine dust, which is highly flammable in blasting systems (especially with zinc flakes). Regulations such as TRGS 900 (occupational exposure limits) stipulate strict limits for dust concentration in the workplace (e.g., 1.25 mg/m³ for A dust). Without active dust removal, these values are immediately exceeded in the case of fine dust (<63 μm).

The recommendation to have the dust tested is a legal obligation within the framework of a risk assessment (GefStoffV).

The main risks of fire and explosion are posed by dust deposits in pipes and dust extraction systems (filter systems). Dust filter systems (with cartridge or bag filters) must be designed to be pressure shock resistant and must be located outdoors. If located inside a building, complex explosion protection measures are required (valves are complex and expensive).

Alternatively, wet scrubbers can also be used. These are cheaper, but also have disadvantages. They have a higher cut point compared to dry filters, so police filters are still necessary to capture the finest dust particles. In addition, sludge is produced, which must be disposed of. Manufacturers generally prohibit the return of filtered air into the building, as the regulations for this are very strict.

These procedural instructions take the following into account in particular:

• IFA / GESTIS – Combustible dusts in blasting systems
  → Information on smoldering nests (hot spots), dust explosion classes, and paint-related ignition risks
• VdS 3445 – Fire protection in dust extraction systems
  → Fire prevention measures, handling of metallic dusts with organic components
• VDI 2263 Sheets 1 & 6 (indirectly referenced)
• DIN EN 1127-1 – Avoidance of effective ignition sources
• ATEX Directive 2014/34/EU
• Other applicable regulations for plant manufacturers (e.g., EN 15089 – Flame arresters, EN 14491 – Pressure relief, EN 14373 – Explosion suppression)

Hazards without curing

• Zinc-containing paints contain organic or inorganic binders which, when blasted,:
  • produce combustible fine dust
  • tend to form smoldering nests (BZ 4)
• According to IFA evaluation, 70–80% of blasting dusts are explosive, especially on painted surfaces
• Increased risks:
  • Filter fires
  • Dust explosions (St 1)
  • Ignition by hot particles or sparks
  • Curing before the blasting process is essential to eliminate organic components.

The process description covers thermal curing, the cooling phase, and the subsequent blasting process after curing.

• Visual inspection after baking (no coating residues, matt ash/oxide layer)
• Random checks of the blasting dust composition (if necessary)
• Documentation in the cleaning and maintenance log

• Incompletely cured paint → cure again
• Noticeable smoke development → stop process immediately
• Fire incidents → take measures in accordance with fire safety regulations