The Dust Sampling Plan

After deciding to carry out combustible dust tests the first thing you should do is to gather dust sample(s) and sent them to the lab, right? Actually, no. NFPA 652 requires that a written sampling plan be developed with a rational reason for why the sample locations were chosen. So what is so important about a written sampling plan?

The purpose of the combustible dust tests is to determine the hazards presented by the dust that is actually in your facility and in your process. The actual hazard presented by YOUR dust may be substantially different than in another facility handling the same type of dust but that has a different process. For example, I have been in a facility that handles grain where the grain goes directly from a storage bin into a process. In this case a sample of grain from the storage bin taken from the storage bin accurately reflected the dust in the system. At the same time a different facility across town used the same grain (it actually came from the same source) but their process included a hammer mill between the storage bin and the process. In this case a sample of grain taken from the storage bin does not represent the hazard in the system because the fugitive dust emanating from the hammer mill and the product stream to the process were much smaller than the dust found in the storage bin and had a much higher explosibility. (See previous entry.) While the grain in both facilities started out the same, the hammer mill process changed hazards associated with the dust. The end result was that the two facilities were very different.

This simple example helps demonstrate why a written plan is required. A written plan requires time to be taken to evaluate and record the reasons why a sample accurately reflects the hazards in a facility. A written plan will help deflect/answer questions if an audit of system or safety documentation were to occur. A non-existent or slipshod sampling plan will leave many questions unanswered and leave the door wide open for further inquiries. On the other hand, a well thought-out and written plan will provide answers to many, if not all, of the auditor’s questions.