In life sciences manufacturing, safety in handling bulk powders and combustible dust can fall through the cracks. The bottom line? As per fire and building codes, if your manufacturing process generates dust, you must perform a dust hazard analysis to establish whether you’re dealing with a fire or explosion hazard. If you are, you need to know how to mitigate the risk throughout your facility.
There’s an understanding that flammable liquids, like pure ethanol, are potential fire hazards and proper safeguards must be in place when handling large quantities. But it’s common in the industry to believe there’s no risk when handling combustible dust. Manufacturers may claim that, since they’ve had no incidents, even after years of operation, there’s no risk.
When working with powder and dust, the risk of combustion is real and must be taken seriously. Always assume dust is combustible until proven otherwise. The need to comply with code exists for a reason.
There are four steps you need to take to evaluate your combustible dust risk and mitigate it.
1. Determine if you have a combustible dust
A combustible dust consists of dust particles no larger than 500 µm presenting a flash-fire or explosion hazard when suspended and ignited in air, according to the National Fire Protection Agency (NFPA). Unlike the definition for a flammable liquid, this code definition is not easily applied to a powder product and additional methods must be used to establish combustibility.
Combustible dust can be suspended in air as a dust cloud or accumulate on surfaces. Combustible dusts can be generated during the manufacture of oral solid dosage products—pills, tablets, capsules, soft gels, gummies—through the use of components, such as powdered organics (e.g., lactose, sucrose) and some APIs in powder form. For example, this is a risk in a weigh/dispense area for dry powder ingredients used in API and OSD processing operations. The fine dust of protein isolate powders used in the making of plant-based protein foods is also combustible.
A flash fire can occur when combustible dust (fuel) is dispersed in the air (oxidizer) and exposed to a source of ignition. A relatively small explosion of powder suspended in air can aerosolize the dust accumulated on surfaces, which can lead to a significantly larger and more destructive detonation.
Without information demonstrating a dust is non-combustible—like a material safety data sheet (MSDS)—you have to assume it is and must send dust samples to be analyzed in a laboratory using standardized tests.
Even when an MSDS says a dust is non-combustible, the way a powder is processed might convert it into a combustible dust. An example is starch pellets that are non-combustible until they’re ground up to combine with an API to make gummies. Or consider what happens when a combustible powder is combined with a non-combustible API to make a tablet. Is the formulated drug product combustible? The only way to find out is to analyze the final product.
Important properties of a combustible dust include:
- Minimum explosion concentration (MEC) – The lowest concentration of a combustible dust when suspended in air that can support a fire.
- Minimum ignition energy (MIE) – The minimum spark energy capable of igniting a dust cloud.
- Kst – The maximum rate of pressure rise describes the explosion severity of a dust cloud.
- Pmax – The maximum pressure spike that occurs upon ignition.
The lower MEC and MIE, and the higher Kst and Pmax, the more explosive and hazardous dust becomes.
You have combustible dust—now what?
2. Undertake a dust hazard analysis
Unlike the flammability of a liquid, which is based on its boiling point and flash point, the combustibility of a powder is more complicated. And, unlike flammable liquids, the presence of dust doesn’t automatically mean there’s a combustion hazard. Instead, it’s dependent on the conditions in which a combustible dust is handled and processed.
Compliance with the combustible dust provisions of NFPA codes is mandatory. You can’t assume a dust is non-combustible and not hazardous, even if you’ve never had an incident in your facility (NFPA 5.2.3) and the code has to be applied to both existing facilities and new construction (NFPA 1.5.2).
NFPA 652: Standard on the Fundamentals of Combustible Dust lays out the requirements for a dust hazard analysis (DHA) for all new and existing processes. A DHA is a review to identify and evaluate the potential fire, flash fire, or explosion hazards associated with the presence of combustible dust in any process system and building area. An authority having jurisdiction (AHJ), like a fire marshal or building permitting officers in a county or state, can request this code-required document.
What’s included in a DHA?
A DHA contains a defined boundary of the scope of the analysis. It documents the combustible powders present within this scope, as well as their properties (e.g., MEC, MIE, Kst, Pmax, and explosion class rating). It also provides a brief description of each application of the ways the powder is handled and processed, including the quantities of powder and whether it uses an open or closed process.
Armed with this data, a manufacturer can determine if a dust is combustible by comparing its properties with known combustible powders, such as powdered sugar, wheat flour, or starch. Alternatively, it can be assigned an explosion class based on its Kst.
Who conducts a DHA?
Per NFPA 652, the owner/operator is ultimately responsible for the DHA, but can use a competent third party to undertake the analysis. Avoid third-party DHAs from those unfamiliar with your process, since they can be more restrictive than necessary or too lax for safety. You have an obligation to follow the recommendations of the DHA regardless, since it is a code-developed document. Instead, choose to have a competent analysis from those who have experience with your industry.
What is the methodology for conducting a DHA?
A DHA analyzes the likelihood of hazardous dust conditions, the probability those conditions lead to deflagration or fire, and the life safety impacts of a deflagration or fire.
Conduct an area-by-area analysis of the risks
A DHA follows the powder through the process, providing a risk analysis of each area in the facility. For each operation this includes identifying the potential for:
- Open flames or hot surfaces
- Sparks from electrical equipment
- Static buildup
- Mechanical friction
- Auto-ignition
Proprietary risk-ranking tool
At CRB, we assign each area a level of risk based on the likelihood of the presence of a combustible dust cloud or adequate accumulation of dust, whether an ignition source is present, and the severity of a potential deflagration, explosion, or fire. The total score for each area is fed into our proprietary risk analysis tool. We then compare this score with code regulations, as well as historical examples from multiple completed projects, which provides an objective analysis. This ranking determines what needs to be done to minimize the risks.
3. Ensure mitigation
For each area, we make recommendations based on the risk analysis related to electrical classification of the room, facility and equipment design, housekeeping practices, and dust control steps. Depending on the risk ranking, appropriate mitigations can range from requiring no action to needing all safeguards in place to meet an unacceptable level of risk. Additional recommendations tend to be high level. For example, equipment needs to be fabricated according to the electrical classification, the equipment may need to be grounded and bonded, the building is designed to minimize dust accumulation, and operations need to take place at temperatures lower than the auto-ignition temperature of the powders.
Case study
Manual pouring spreads dust
A manufacturer making nutraceutical tablets performs small volume tableting operations by filling five- or 10-gallon sacks with powder and manually carrying those sacks to an elevated platform. At the platform, the operator used to open the sack and hand-scooped material into the feed chute of the tablet press.
Observation of the process revealed that, even though the operator was careful, over time powder would accumulate on top of the tablet press to a depth that made it impossible to see the surface color of the top of the press. In addition, the operator told of a time when the open sack of powder was accidently spilled and material fell from the platform to the floor, like a waterfall, causing a thick plume of powder to cascade throughout the small room.
Combustible dust presents an explosion risk
Third-party testing determined the powder was combustible with a Kst indicative of explosion class St 1. CRB conducted a dust hazard analysis on this process, resulting in identification of a significant risk. The area was classified as a Class II, Div 1 environment, meaning powder was present in sufficient quantities during normal operations to support a deflagration. We recommended the manufacturer significantly improve housekeeping measures—essentially cleaning as they went—until they were able to close the system by installing a vacuum transfer system with closed piping to the tablet press.
4. Find a DHA partner
Combustibility of powder operations is often overlooked by our clients despite the NFPA requirement for the evaluation of all dusts to establish their level of explosivity. Typically, a manufacturer won’t have this information on-hand for their dust products, but it’s easily attainable from reputable labs around the world. A dust hazard analysis is essential to determine the level of risk within each step of the process and the proper level of mitigation to address the risks.
CRB has the experience to partner with you to deal with dust hazards in your operations. Our services include evaluating third-party data to determine level of combustibility, performing DHAs, and risk mitigation. Bringing these services in-house allows us to perform a DHA specific for your process. We conduct the DHA early enough in a new construction that our engineers are able to implement its recommendations without unforeseen cost or schedule impact. It ensures we carry out a proper level of risk assessment and provides project controls so we can identify a proper scope of work—we are able to control the project.
