NFPA 652-2016, Standard on the Fundamentals of Combustible Dust, provides the basic principles of and requirements for identifying and managing the fire and explosion hazards of combustible dusts and particulate solids. The standard is intended to provide the minimum general requirements necessary to manage the fire, flash fire, and explosion hazards posed by combustible dusts and directs the user to other NFPA standards for industry-specific and commodity-specific requirements.
The standard contains requirements for dust hazards analysis (DHA) which is a systematic review to identify and evaluate the potential fire, flash fire, or explosion hazards associated with the presence of combustible particulate solids in a process or facility. DHA is part of a prescriptive approach to combustible dust safety but a performance-based approach can be used which relies of a dust risk assessment (DRA).
A DRA involves an assessment of the likelihood, vulnerability, and magnitude of the incidents that could result from exposure to hazards. It is a process that:
1. Identifies hazards.
2. Quantifies the consequences and probabilities of the identified hazards.
3. Identifies hazard control options.
4. Quantifies the effects of the options on the risks of the hazards.
5. Establishes risk tolerance criteria (maximum tolerable levels of risk).
6. Selects the appropriate control options that meet or exceed the risk acceptability thresholds.
Steps 1 through 3 typically are performed as part of DHA.
DRAs can be qualitative, semi-quantitative, or quantitative. Qualitative methods are usually used to identify the most hazardous events. Semi-quantitative methods are used to determine relative hazards associated with unwanted events and are typified by indexing methods or numerical grading. Quantitative methods are the most extensive and use a probabilistic approach to quantify the risk based on both frequency and consequences.
Many practitioners will favor the use of risk matrices, which are commonly used in process hazard analysis (PHA), and layers of protection analysis (LOPA), which is a useful step beyond risk matrices that provides more objective risk estimates. Fully quantitative risk assessment likely will be used only for the most severe hazards.
Further guidance can be found in:
Procedure for dust hazard analysis (DHA), Primatech white paper.
P. Baybutt, Process Hazards Analysis, in Handbook of Loss Prevention Engineering, Wiley-VCH, Weinheim, Germany, 2013.
P. Baybutt, Layers of Protection Analysis, in Handbook of Loss Prevention Engineering, Wiley-VCH, Weinheim, Germany, 2013.