Client Background
The company operates a cereal processing and packaging facility in the UK, producing rolled oats and oat flour for the UK retail market. The site has four milling lines, each with hammer mills, pneumatic conveying systems, and cyclone separators. A central baghouse dust collector services multiple process streams.
Client Problem
Operators on Line 3 noticed intermittent surges in the pneumatic conveying system.
Unknown to them, the reverse pulse filter cleaning system was partially blocked leading to reduced airflow that allowed fine oat flour to settle inside ducting.
A spark from a misaligned metal component in the hammer mill ignited the suspended dust cloud within the mill housing. The resulting primary flash fire was largely contained within the equipment, but the overpressure caused dust to be dislodged from overhead beams in the surrounding area.
Client Objectives
The client needed to understand how and why the event occurred. While early findings suggested equipment failure, there were indications that deeper issues played a role. To gain this clarity, Sigma-HSE undertook a structured root cause analysis.
Insights and results
The root cause analysis identified the following contributing factors:
Mechanical Failure
The hammer mill had not been inspected for over 18 months. The worn rotor created a partial blockage. The reverse pulse filter cleaning system had been inspected, but the documentation confirming this was missing.
Dust Accumulation
Housekeeping audits were irregular. Significant deposits of fine dust were found on horizontal surfaces and in poorly ventilated areas.
Ignition Source
The hammer mill’s internal wear plates were overdue for replacement. Metal-to-metal contact produced sparks.
Deficient DSEAR Compliance
The last hazardous area classification and risk assessment was five years old and did not account for changes in production volume.
Organisational Culture
Operators reported a culture of “fix it when it breaks” rather than preventive maintenance. Production demands were prioritised over scheduled shutdowns.
