DSS062: Designing Hose Systems to Handle Combustible Dust with Ross Blanford

In this episode of the DustSafetyScience Podcast, we interview Ross Blanford, Director of Sales at Masterduct Inc in Houston, Texas, about designing hose systems to handle combustible dust. Masterduct is a leading global manufacturer of flexible hose and ducting products and has over 30 years’ experience in providing the right products and utilizing the right materials for harsh and hazardous areas.

The inspiration for this episode was an article that Dr. Cloney sent to Ross. It was an overview of the 2007 Cordero Flour Mill explosion in Cuneo, Italy, which fatally injured five workers. A truck was being loaded with flour. When they used a rubber hose to load remnants, electrostatic charge built in the hose, igniting an explosion that propagated back to the silo and triggered an explosion in the head space.

This incident raises important questions, namely how well-known is this ignition source (hoses) and what precautions need to be taken? Ross, who will be presenting at the 2020 Digital Dust Safety Conference, is the best person to answer them. During this interview, he also answers questions like:

What are the different types of hoses for powder and dust conveying operations?
What industries might require these type of different hose designs in their systems?
How are hose systems certified for anti-static and electrical conductivity?
What are some difficulties with industry adoption of safe amounts of conveying hoses?
Are any new innovations coming out?

What Are The Different Types Of Hoses For Powder And Dust Conveying Operations?

“One of the frustrating things about being in the hose and ducting business is the assumption by many in the end user community that hose is just a hose,” Ross said. “On some level, that may be correct for an ordinary application or for a commercial application. For industrial applications, the opposite is true. And while many products on the market look similar, there are differences in performance and design, the safety of those using the products, and in the areas where the products are utilized.”

There are many different hose materials that can be used, including PVC, EPBM, rubber, fabric, and metal hoses. With combustible dust, the best solutions for conveying these products and for housekeeping in these environments are polyester, polyurethane, and thermoplastics as well as fabric hoses made of specific materials. They’re generally available in two different styles.

Thermoplastic Hoses

There are many different types of thermoplastic, but polyurethane is the best choice because it is more durable for industrial environments and the aggressive sort of media that tends to be transferred in combustible dust applications.

The thermoplastic polyurethane material used to manufacture the hose should have an additive in the material that makes the hose anti-static. The industry standard rating for the electrostatic level is between 10 ohm sub to the fourth and 10 ohm sub to the ninth. Grounding straps and other technologies can also be incorporated by connecting the hose or duct to dead metal that allows the static charge to ground.

An additional benefit of the polyester polyurethane hoses is that their durable quality and resistance to friction enable them to outlast PVC hoses and other hose materials at least three to one. So not only are they safer, but they also provide additional value to the end user.

Electrically Conductive Hoses

The first version of this hose type is also made from polyurethane and has the same wire helix as the anti-static version, but they’re also impregnated with carbon black material to add to the hose’s electrical resistance properties.

Because of these extra features, electrically conductive hoses are rated higher than 10 ohm sub to the fourth. They provide maximum protection against arcing and sparking caused by the electrical conductivity on their surface. A quality manufacturer will test the electrical resistance of each section of hose to the appropriate ohm rating as it’s being made to assure safe performance of the product in the field.

The difference between anti-static and electrically conductive hoses is that the additive in the anti-static hose prevents a charge from forming on the surface up to a certain point, whereas the electrically conductive hose uses a grounding wire and grounding mechanism to move any static that does form safely to ground.

What Industries Might Require These Type Of Different Hose Designs In Their Systems?

Under the SIC code system in the US, there are dozens of industries that need safe transport hoses in material conveyance and housekeeping applications where combustible dusts are present.

“Some of the more common (industries) that we see requests from are plastics manufacturing, wood products manufacturing, and metalworking applications where the metal dusts have a high risk for explosions, such as aluminum, titanium and the like,” Ross explained.

He added that Masterduct does a lot of business with chemical fume extraction facilities where the fumes are explosive, and companies that do jet fuel processing or store food and beverages because they not only require the electrical safety, but they also need hoses that are made of FDA-compliant materials.

Ross pointed out that electrically conductive hoses are a good idea in any application where there’s a combustible dust in sufficient quantities to cause an incident. “The classic fire triangle is very much in play in these applications. For the most part, it’s up to the facility management to understand the NFPA standards and identify the best hose technology based on the results of their dust hazard analysis testing.”

How Are Hose Systems Certified For Anti-Static And Electrical Conductivity?

Under the current standards in the US, the equipment that hoses are attached to are all certified under NEC 500 or NEC 501 to a class and division or a class and zone sort of system for safe operation where combustible dusts are present.

“There isn’t a standard written into the National Electric Code for hoses as a part of the system used to handle these combustible dusts,” Ross said. “When I approached a third-party testing agency to ask why, it was explained to me that under ATEX and IECx, the certification is more of a system certification, whereas in the US, the certification process is more on individual components of a system.”

Although dust collectors, industrial vacuums, baghouses and all the other types of equipment that are involved in processing combustible dust are required to be tested and certified, this is not the case with hoses.

When addressing hoses and other flexible products, the National Fire Protection Association and, specifically, NFPA 652 refers to hoses and ducting as flexible connectors, specifically in Section 8 where they talk about housekeeping. All that’s required for hoses and tools is that they are static dissipative or conductive. In Section 9, it states that vacuum cleaning hoses should be static dissipative or conductive and grounded. No distinction is made between conductive, anti-static dissipative and or the difference between the two.

Section 9 contains more specific information on flexible connectors. According to the subsections, flexible connections in atmospheres containing combustible dust and/or flammable vapours that are longer than two meters or 6.6 feet need to have an end-to-end resistance of less than 10 ohm sub to the 8 to ground with an internal or external bonding wire connected to the equipment with the flexible connector

For atmospheres where there are no flammable vapours present but there are combustible dusts, flexible connectors are allowed that have a lesser degree of conductivity, which is defined as equal to or greater than 10 ohm sub to the eight under certain conditions.

“I talked to one of the NFPA committee members this week about these particular sections and why they were included,” Ross said. “It was explained to me that the reason these sections were included in 652 is that during investigations into explosions, it was found that hoses designed to be static dissipative or conductive that have experienced excessive wear or that are poorly installed are no longer safe and are contributing to these incidents.”

The sections include some examples of testing methodology. Rather than being a standard of performance, they state that each hose, if it were tested in this way, would be expected to perform at specific ohm rating levels in order to be considered safe. This point stresses the importance of choosing quality hoses and ducting and replacing them as needed.

I can’t tell you how many times I’ve been into a plant with and without combustible dust and seen hoses covered in duct tape and hoses desperately in need of replacement,” Ross said. “But sometimes the budgetary issues outweigh the safety based on a lack of education on these topics.”

Under ATEX, there are specific codes written around the hose technology. In Germany, where Masterduct’s parent company is based, GAS 727 is the standard associated with hose and ducting performance. The products made in Germany are certified to this standard and therefore compliant with the ATEX directive.

What Are Some Difficulties With Industry Adoption Of Safe Amounts Of Conveying Hoses?

Ross pointed out that regardless of the type of explosion protective equipment, there is a lot of ambiguity in the terminology used. For example, under the way the codes and standards are written, explosion-proof means one thing but people may mean something else when they use the term.

Likewise in the hose and ducting industry, the terms anti-static and electrically conductive mean different things and are applied in different areas for very specific reasons. But to a lot of people, these terms are interchangeable. This leads to confusion about whether or not these products are necessary and which technologies should be used in certain locations and applications.

“The other issue is cost,” he added. “Obviously, budgets are always an issue and electrically conductive hoses are more expensive. So in many cases, it’s assumed that anti-static hoses are good enough when in almost all cases, electrically conductive hoses would be the best possible solution when hazardous dusts and or vapours are present in an environment.”

He also identified lack of more specificity in certain areas of the standards as being a problem. Facility managers and safety people are left to educate themselves and implement their individual or corporate product selection standards when and if they choose to make it a priority.

Are Any New Innovations Coming Out?

Ross said that he’s always asked how long a hose will last in a certain application, but the only way to determine product longevity is to test it in that environment to see how it performs.

In 2018, Masterduct’s parent company in Germany, Masterflex, announced a new hose system technology under the family name of Ampius. The company began equipping hose systems with a digital interface that, in combination with the Ampius mobile app, allows customers to receive an interactive display of technical data associated with the specific hose as well as lifecycle data. This information would allow the customer to prevent downtime, improve their operations and save money.

Conclusion

Ross pointed out that there is still a real lack of education on the role that hose technology plays in material transfer safety. “We (Masterduct) want to educate facility management on the importance of hose safety and provide the end user with a quality product that will contribute to the safe handling of combustible dusts.”

If you would like to discuss further, leave your thoughts in the comments section below. You can also reach Ross Blanford directly:
Email: [email protected]
LinkedIn: https://www.linkedin.com/in/rossblanford/
Cell: 832-593-2440

If you have questions about the contents of this or any other podcast episode, you can go to our ‘Questions from the Community’ page and submit a text message or video recording. We will then bring someone on to answer these questions in a future episode.