The new NFPA 652-2016 Standard aims to improve management of combustible dust through assignment of responsibility and introduction of plans and procedures, regular inspection of ignition sources, and limitation of the impact of a deflagration or explosion through construction, protection, insulation and cleaning (maintenance).
The standard’s four key principles are:
- Life safety
- Mission continuity
- Mitigation of fire spread and explosions
- Compliance following a prescriptive approach or a performance-based design approach
This article takes a closer look at a plant owner’s obligations with respect to combustible dust hazards. In Canada, provincial occupational health and safety statutes require that any hazards to which a company’s employees or subcontractors are exposed be identified and that related control measures be implemented.
In addition, workers exposed to such hazards must be given appropriate training and be provided with protective equipment. The NFPA 652-2016 Standard is in agreement with these requirements and allows for their specification when combustible dust is present.
Under NFPA 652-2016, the owner is responsible for:
- Determining the combustibility and/or the explosibility hazards of existing materials at the plant (e.g., combustible dust)
- Properly identifying, assessing and managing all the fire, flash fire and explosion hazards associated with combustible dust
- Communicating the hazards to affected personnel and employees (including subcontractors)
Step 1: Determining combustibility
Owners of industrial installations are frequently unaware that their processes generate combustible dust or that combustible dust is found at their facilities. As a result, they have no idea of the dangers combustible dust represents in terms of fire, flash fire or explosion. When dust, powders or other residues at an industrial facility are thought to be combustible, the owner must ascertain whether or not those materials are ignitable by identifying:
- Normal and abnormal production conditions
- The nature of the products at the plant
- The combustibility and explosibility of these materials through either:
- Data deemed representative for the material and process in question
- Laboratory analysis of a dust sample from the site
Note that the NFPA 652-2016 Standard makes recommendations regarding the representativeness of samples and safeguarding sample integrity. Although laboratory analysis procedures are clearly established under ASTM, EN, and other standards, there is no official procedure or protocol for on-site sample collection.
Just because there has been no incident or accident to date does not mean the dust at an installation is non-combustible or non-explosive (a. 5.2.3) and, therefore, without danger. For example, with over 20 years of experience in the field as risk management experts, BBA engineers often face comments like “I’ve worked here for 25 years and there’s never been a problem with dust!” or “We experimented in the yard and the dust doesn’t burn—even with a blowtorch!”
Given the consequences of a wrong diagnosis on dust combustibility or explosibility, and because “representative sampling” can be a significant challenge in an industrial context, owners should hire an outside expert for the first phase of determining whether materials at the plant are combustible.
Step 2: Identifying, assessing and managing hazards
Plant owners must ensure that a risk analysis for combustible dust is carried out at their industrial installations. The NFPA 652-2016 Standard clearly defines what must be included in a dust hazard analysis (DHA). The DHA is both mandatory and retroactive!
The analysis must :
- Identify at-risk areas: identify the location of all sectors and buildings as well as all equipment used for processing, treatment (e.g., dust collectors, cyclones) and storage (e.g., silos) where combustible dust is likely to be found or produced.
- Analyze potential ignition scenarios: identify possibilities and mechanisms that may lead to fire, deflagration or explosion under normal and abnormal operating conditions. All ignition sources must be assessed and all known hazards must be properly identified:
- Reactivity hazards (e.g., aluminum or oxidizable metal dust + water reactivity)
- Smoldering fire (layer or pile of particle solids)
- Flaming fire of a layer or a pile
- Deflagration resulting in flash fire
- Deflagration resulting in dust explosion in equipment
- Deflagration resulting in dust explosion in rooms and buildings (e.g., secondary explosion)
- Identify the measures to be applied: formulate recommendations and inspection solutions to mitigate and manage identified hazards.
The analyses and technical recommendations must be made by qualified persons, within the meaning of the standard, who will be responsible for the results and opinions expressed. A qualified person must have:
- The right training
- Relevant experience
- The necessary knowledge
- Proven skills
To conduct a DHA, the plant owner must set up a multidisciplinary team that is generally led by qualified persons. The team typically includes resources who are familiar with:
- Process and maintenance operations
- Process equipment
- Protection devices (e.g., detection, fire, explosion) and emergency procedures
- Operational history
- The properties of the material at the plant
Step 3: Hazard communication and hazard management system
Owners are responsible for implementing a hazard management system, which must be retroactive under the NFPA 652-2016 Standard. This means the employer is responsible for creating operating procedures for safe operation of the installations and equipment in order to prevent or mitigate the risk of fire, flash fire and explosion.
It is good practice for a program to include:
- Training requirements: to inform all personnel about existing hazards:
- For employees, contractors, temporary workers and visitors: training and hazard awareness regarding combustible dust, based on their level of exposure
- For maintenance staff: training on how to operate protective and preventive devices
- Safe operation requirements: to implement operating procedures and practices that will lead to a maximum level of protection, as well as inspection and maintenance requirements for:
- Process equipment (e.g., lubrication of bearings)
- Control equipment (e.g., dust collection systems)
- Protection devices and systems (e.g., fire detection, spark and ember detection, deflagration venting, chemical suppression)
- Emergency procedures: to establish emergency planning and response requirements (e.g., Emergency Preparedness Plan – EPP) in the event of a fire, a flash fire, an explosion or any other incident; such a plan must be reviewed and validated at least annually
- Incident investigation system: to make sure that any incident (e.g., fire, deflagration) is well and promptly investigated, and that relevant findings are properly addressed
- Management of change: to implement follow-up measures that ensure the protection and mitigation actions continue to be applied, per the requirements of the NFPA 652-2016 Standard. The following temporary or permanent changes will have to be addressed:
- New materials (process)
- Changes in work teams and the assigned tasks
- Replacement of technology and process equipment
- Changes to procedures, installations and buildings
The NFPA 652-2016 Standard published in September 2015 requires that a number of measures be implemented to manage the fire, deflagration and explosions hazards associated with combustible dust.
Under the standard, the owners of industrial installations must ensure that the combustibility and explosivity of materials at the plant has been determined and that all hazards linked to the presence of combustible dust have been identified and properly managed. It is also their duty to effectively inform employees and subcontractors of the kind of hazards found at the plant and to introduce a follow-up and change management plan to make sure that the protective and mitigation actions will continue to be applied.
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