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Safe Confined Space Entry for Chutes, Silos and Hoppers

Edited by mhd on 31. Jan. 2020
An estimated 7% of the U.S. fatalities recorded by MSHA between 1995 and 2011 occurred in a confined space. To reduce that number, conveyor operators are wise to understand exactly how a confined space is defined, and to consider what they can do to prevent serious injuries.
Proper air cannon placement in chutes and silos can reduce ongoing buildup. (© Martin 2020)
Proper air cannon placement in chutes and silos can reduce ongoing buildup. (© Martin 2020)

Many factors can cause bulk materials to adhere to the sides of chutes, silos and hoppers – including humidity, moisture content, size/texture of the raw material or increased production volume – resulting in lost capacity or clogging. Ongoing accumulation reduces flow and eventually stops production in order to address the issue, causing expensive downtime and requiring extra labor to clear the obstruction.

“Clearing extensive buildup often involves confined space entry, but the consequences of untrained staff entering a chute, silo or hopper can be disastrous, including physical injury, burial and asphyxiation,” said Product Engineer Daniel Marshall. “Without proper testing, ventilation and safety measures, entering vessels containing combustible dust could even result in a deadly explosion.”

What is Confined Space Entry?

An estimated 7% of the U.S. fatalities recorded by MSHA between 1995 and 2011 occurred in a confined space. (© Martin 2020)
An estimated 7% of the U.S. fatalities recorded by MSHA between 1995 and 2011 occurred in a confined space. (© Martin 2020)

The Occupational Safety and Health Administration (OSHA) defines “confined space” as an area not designed for continuous employee occupancy and large enough for an employee to enter and perform assigned work, but with limited or restricted means for entry or exit. [1] “Permit-required confined space” means a confined space that has one or more of the following characteristics:

  • The vessel contains or has the potential of containing a hazardous atmosphere such as exposure to explosive dust, flammable gas, vapor, or mist in excess of 10 percent of its lower flammable limit (LFL). Atmospheric oxygen concentration below 19.5 percent or above 23.5 percent;
  • There is the potential for material to engulf, entrap or asphyxiate an entrant by inwardly converging walls or by a door which slopes downward and tapers to a smaller cross-section; or
  • Contains any other recognized serious safety or health hazards.

Entering a Confined Space

Working in confined spaces typically requires:

  • Special personnel training
  • Safety harness and rigging
  • Extensive preparation
  • Added personnel for a ‘buddy system’

“Systems designed to minimize permit-required confined spaces can provide a significant return on investment, and the best time to reduce the amount of confined-space entry for component maintenance and replacement is during the specification and design stages of a project,” Marshall continued. Many manufacturers offer systems and products that can reduce the need for confined space entry.

Never do this: confined space entry by untrained personnel is a formula for serious injury. (© Martin 2020)
Never do this: confined space entry by untrained personnel is a formula for serious injury. (© Martin 2020)
The rear chute wall in this image is bolted onto side flanges, allowing safer access. (© Martin 2020)
The rear chute wall in this image is bolted onto side flanges, allowing safer access. (© Martin 2020)

Examples would include:

  • Modular chute designs with abrasion-resistant liners.
  • Chutes that hinge open and lay down for liner replacement.
  • Skirtboards with external liners.
  • Belt cleaners that can be serviced without confined space entry.
  • Flow aids such as air cannons and vibrators to reduce buildup.
  • Modular air cleaners for specific locations rather than centralized dust collection.
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