(193d) Case Study: The Importance of Reliable Inertisation and Earthing of Ignition Sensitive Powder Handling Systems

This ?learning from? will show how ignoring a defect on a magnetic sieve lead to the eventual increase of oxygen in a powder handling system to the point that an ignition occurred, probably through an electrostatic discharge, resulting in a fire. The electrostatic charge build up probably occurring due to insufficient earthing of a conductor.

This case study will attempt to reconstruct the incident and include fire and explosion data for the material(an antioxidant for the plastics industry of low Minimum Ignition Energy) being handled.

The identified causes of the incident will be shown and the measures chosen given.

One organisational measure, in particular that of SAMACO(Safety Maintenance and Control) was chosen.

The aim of this paper is to encourage people to establish a system of simple but regular controls of specific safety equipment, using their operation staff, in so doing reduce the probability of incidents.

A SAMACO systematic will be presented in depth.

The main message:

Involve your process operators in some well chosen and regular controls of equipment required to ensure safety.This will help reduce incidents, improve safety and reduce unplanned downtime.

The Incident

In one of our powder handling plants in the Asia North region there was a fire.

The operators noticed something burning and investigated.

They found burnt product in and around a particular piece of equipment used to mill powder

The Causes

? The investigation showed that air had leaked into the equipment through the lid of a magnetic sieve which was partially open.

? The lid had a fastener which had broken but had not been fixed for some time.

? The dust flowing from the equipment above down to the mill causes electrostatic charge separation.These charges built up on the magnetic sieve because the magnets were conductive but not earthed. Most probably a spark discharge occurred between the magnets and the earthed housing of the magnetic sieve.

? The dust and air concentration was high enough to make an ignitable mixture and this caught fire.

Technical measures

? The lid fastener was repaired

? The magnets were actively earthed using copper earthing cable

? Additional nitrogen inlet points were installed

Organisational measures

? Management put in place controls of the integrity of the system through regular checking of the sealing and earthing of the equipment.These are done and recorded by the operators on a regular basis. If they see something not right they deal with it right away.

This programme used here is what we call SAMACO(Safety Maintenance and Control)

The 4 steps to implementing SAMACO

Step 1: Chose the crucial safety equipment you want to control and check

Step 2: Define what controls you want to do and how often

Step 3: Choose who will do the controlling

Step 4: Appoint a coordinator who will oversee the programme

Review the programme

? Management should review the success of the programme regularly

o Is it having the effect that it should?

o Are we seeing less breakdowns and incidents?

o Are we controlling the right equipment?