A staged explosion is used to test a dust collector

Vacuuming Up to Prevent Dust Explosions

Industrial vacuum cleaners or wet/dry vacuums can help to prevent the development of dust clouds or electrical sparks that can be generated by compressed air systems.

In recent years, OSHA has increased its surveillance of facilities that generate or handle combustible dust, as part of its Combustible Dust National Emphasis Program (NEP). One of the more startling things OSHA has found in the course of this program is that many of these facilities were not even aware they were handling what is considered combustible dust, nor were they aware of the safeguards necessary for the safe handling and removal of dust and related materials from industrial locations.

This increased monitoring has come about as a result of more than 280 dust incidents of varying severity that occurred between 1980 and 2005. During this period, 119 workers were killed and more than 700 were injured in dust explosions.1 In addition, many of the facilities in which explosions occurred were extensively damaged.

OSHA reports many of these dust-related problems can be corrected if facilities revamp their housekeeping practices. This includes training cleaning workers on best practices for cleaning and removing dust from industrial locations. Dust from floors and other areas often is removed by sweeping or using air movers, including those not designed for potentially hazardous conditions. Both of these practices can lead to explosions and are among the top violations cited by OSHA. In fact, several of OSHA's documents—such as the "Dust Control Handbook for Minerals Processing"—specifically state that operations should "eliminate the use of compressed air jets to clean accumulated dust from the equipment or clothing [of workers] and substitute a vacuum cleaning system."

Taking this a step further, they also recommend that cleaning workers use vacuum systems that "clean spills and dust accumulations…[and] avoid brooms and shovels," in essence suggesting the use of industrial vacuum cleaners or wet/dry vacuums designed specifically to vacuum up dust and debris, as well as liquids and spills. Using these systems can help to prevent the development of dust clouds, which can easily be triggered into an explosion, or electrical sparks that can be generated by compressed air systems, which also can result in an explosion.

Industrial Vacuum Systems
The first industrial vacuum systems designed for use in industrial locations were introduced in 1954. They were developed specifically for use in textile mills, which historically have had serious problems with both dust and explosions. However, when most people--even in industrial-type facilities--think about industrial or wet/dry or similar vacuum systems, they think of shop-type vacuums, such as those purchased in hardware stores.

Some facilities even have attempted to employ these shop vacuums in industrial locations and found them to be ineffective at removing industrial dust and heavy debris. In addition, they can create electrical sparks that could prove hazardous. Because these hardware-store systems are typically designed for residential use, when they are used for heavy-duty cleaning in industrial settings, their life expectancy is often reduced, making them cost prohibitive. A more appropriate option would be an industrial jumbo vac designed specifically for industrial cleanup, described later.

While they differ in design and capabilities, shop and industrial wet/dry vacuum cleaners typically work similarly. The vacuum motor and fan are situated over the machine, which often looks like a large bucket or can. The vacuum creates an airstream, allowing the wand to collect dust and liquids and pull them into the bucket; at this point, the airstream slows down, allowing the droplets, heavier dust, and debris to fall out of the airstream and down into the bucket. The lighter items collect into external filtering systems. In most cases, after vacuuming is completed, the user removes the motor/vacuum system on top of the bucket and empties the filter bags.

"The beauty of some of these systems," said Sean Martschinke, product manager for Tornado®, which manufactures a wide variety of wet/dry and industrial vacuum cleaners, "is the ability to quickly recover large amounts of either dry and wet material. Depending on the type of recovery required, most users can find an industrial vacuum to fit their needs, allowing operators to complete their cleaning tasks faster and more effectively."

According to Martschinke, debris that can be picked up with more advanced and effective wet/dry systems, often called jumbo vacs in industrial locations, includes the following:

  • Heavy oils
  • Sludge
  • Iron dust and chips
  • Sandblasting remnants and pellets
  • Slag and scale
  • Sawdust
  • Flour

"Quite obviously, a shop vacuum purchased from a hardware store was never designed to clean and remove this type of debris, at least on a regular basis," Martschinke added. "Selecting the right industrial vacuum system from the start is not only a cost savings and more effective, but can promote safety, as well, which can mean preventing an explosion."

How to Select an Industrial Jumbo Vac
Martschinke said while there are many types of industrial vacuum cleaners, there are two main types, air powered or electric powered. If working in an environment where reducing the risk of explosions is a factor, then select an air powered unit. Typically, the options are single-air, dual-air, and quad-air jumbos. Also, most manufacturers offer both a wet/dry vacuum and a wet-only vacuum.

The single-air system has one vacuum motor appropriate for recovering water, cutting and machine oil, solvents, and powders. This system should have a minimum of 15 hp and maintain 30 to 60 psi (pounds per square inch, a way of measuring the power of the vacuum system) for light recovery and 60 to 100 psi for removal of heavier debris. A 15 hp compressor will normally provide enough power for this type of unit.

The dual system, as the name implies, has two vacuum motors and is designed for the recovery of heavier items, including heavy oil, paint stripper, sawdust, and general plant debris. "The dual unit requires 90 cubic feet per minute and 100 psi for maximum pick-up, which is normally provided by a 25 hp compressor. It also requires a 3/4-inch input airline," he said.

The largest jumbo Martschinke described is the quad-air machine, which has four vacuum motors and is designed for very heavy-duty cleaning operations. This unit requires input of 180 cfm and 100 psi. This is usually provided by a 5- hp compressor. With 50 hp and psi of 50 to 100, "I would recommend this system for manufacturing and industrial plants. Otherwise, one of the smaller units will likely meet most industrial location [wet/dry vacuum] needs," he explained.

All of these systems are fitted with a 55-gallon steel drum, which he said is necessary for use in an industrial location. This allows for larger debris recovery and reduces the number of debris dumps, which helps to improve worker productivity.

Some final advice Martschinke offered is to understand the difference between cfm (cubic feet per minute) and water lift, both of which should be listed on the machine. While both measure the recovery capabilities of the machine, they are not the same. "Water lift is primarily a measure of the effectiveness of recovering liquids," he said. "However, the cfm indicates how much air moves through the unit and how well the unit will recover dry debris. If looking to recover liquids, select a machine with a higher water lift, but if the task calls for recovering dry debris, the machine should have a higher cfm. The higher the rating, either cfm or water lift, typically translates into more rapid recovery."

References

1. U.S. Chemical Safety Board; http://www.csb.gov/assets/1/7/UFCW.pdf

This article originally appeared in the September 2014 issue of Occupational Health & Safety.

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