DSS018: Top Five Mistakes Companies Make in their Dust Collection System Design with Diane Cave

In this episode of the Dust Safety Science Podcast, we talk to Diane Cave, Regional Manager of Eastern Canada at Element6 Solutions. Diane has over 15 years’ experience with dust collection system design, explosion protection systems, combustible dust hazard assessment, and NFPA compliance.

You may remember that in Episode Four, we interviewed Jeramy Slaunwhite about the Nova Scotia dust collector safety program. Diane was one of the explosion protection specialists working on those 150 or so dust collection systems that were audited by the province. In the current episode, she shares the top five mistakes she has seen companies make in their dust collection system design.

Mistake No. 1: Un-engineered modifications to the dust collection system design

When facilities install a dust collection system, it’s engineered for the equipment in place at the time. The problem is that processes change: machinery and equipment are added, subtracted or replaced but the dust collection system is not updated accordingly. The employees may add more ducting or a hood, or dead-end ducts, but these are not taken into account in the current status of the dust collection system.

Diane has walked into facilities where there have been three or four more branches added to the original engineered system. The manager may not see it as a problem because the same amount of air is involved, when in reality there are now issues because:

Static pressure and airflow requirements in the system have been changed, which affects where the air goes.
In many cases, the air required at a certain hood is starved, and the hood won’t pick up the dust because the air isn’t moving fast enough.

Mistake No. 2: Undersizing the fan

Several factors could result in the dust collector fan being undersized:

Static pressure from the hood through the ducting back to the dust collector must be calculated correctly
Dirty bags reducing the efficiency of the dust collection system
The presence of a return air system

Over time, the dust collection system will wear down, and if that wear and tear isn’t accounted for in the sizing of the fan, it will lose flow over time and dust could end up settling in the ducting.

When Diane sizes a dust collection system, she allows for certain parameters for that eventual relaxing of the system. They include:

Four to six inches of pressure loss across a dust collector for dirty filters
Allowing for flexibility in fan sizing so that over the lifecycle of the system, there will never be a point where the flow at the hood velocity is so reduced so that it can no longer pick up material.

Mistake No. 3: Underestimating airflow requirements at the hood

Diane often sees people underestimating the necessary airflow requirements for the hood. For example, if no one accounts for how much material a saw is spitting out and the air isn’t taking away the material fast enough, it can choke the hood and cause it to stop working.

For example, if an application moves material at 2,000 feet per minute but the hood has only a face velocity of two hundred feet per minute, the dust will just blow past it. You have to account for the application to make sure that your hood is sized with enough air to actually catch the dust.

Diane recommended a handbook called Industrial Ventilation: A Manual of Recommended Practice for Design, which includes parameters and guidelines for hoods and airflow.

Mistake No. 4: Putting the hood in the wrong location

Diane has walked into many facilities where the hood is placed in the wrong location. For example, with a conveyor belt system dust is created when the material is dumped from one belt onto another. The logical move would be to put the hood at that transition point, but she has seen instances where the hood is three feet up on the conveyor, away from the dumping point.

Facility managers often assumed that a dust collection system is like an HVAC system: it can be positioned three or four feet from a source and still suck in dust. Diane recently visited a facility with four-inch ducts coming down and the hood sitting six feet above the dust source, which was a powder-dumping application. The powder dispersed before the dust collection system could take effect.

Mistake No. 5: Not having a hood

The fifth mistake is not having a hood at the dust pickup location. Diane called this an ‘elephant trunk’ hood where they may take a vacuum hose or a chunk of six-inch pipe and tack it on the end of the system. This does not usually work well. With a tapered hood, there is a wide-enough airflow for collection.

Other Challenges

Diane mentioned additional challenges to the effectiveness of a facility dust collection system.

Pedestal fans. In warmer climates, pedestal fans are often used in facilities without air conditioning. When the fan is pointed directly at dust sources, it blows the dust away from the hood, which is not designed to fight against the airflow created from a pedestal fan.
Incorrect duct diameter size. If a duct is six inches and the dust source is more than six inches away, the effectiveness of the system is diminished. If a twelve-inch tapered hood is installed, the distance for collection is doubled.

Conclusion

Diane’s observations led her to believe that facilities have become complacent about how well their dust collectors work. They find it acceptable if the system only picks up 20% of the dust when it should be collecting over 90%. There’s a large disconnect between how dust collectors should operate and how they actually work in the field, but it’s a situation that can hopefully be corrected using awareness and education.

If you would like to discuss further, leave your thoughts in the comments section below.

You can also reach Diane Cave directly:
[email protected]
1-920-476-1269
LinkedIn