Exploring Pneumatic Conveying Technology for Dry Bulk Solids from a Health and Safety Perspective
Common areas of increased profitability and safety when implementing a vacuum conveying system for transport of bulk dry materials.
- By Doan Pendleton
- Aug 01, 2024
Workplace injuries in any organization take a bite out of profits. There is a wealth of data, statistics and surveys from scores of organizations regarding occupational illness and injuries. The statistics regarding the number of injuries and illnesses that occur on the job and purported annual costs of 250 billion dollars is astronomical and difficult to digest at an organizational level and can therefore dilute the significance of injury costs to a single organization.
To bring these costs closer to an organizational level it is necessary to first identify the most common injuries and illnesses in the manufacturing arena. In the goods producing industry, which accounts for account for 35 percent of all occupational illness and injury cases, “manual materials handling is the principal source of compensable injuries,” according to OSHA.
When practical, designing the hazard out of the process through engineering is the best practice for reducing them. While 4 out of 5 manual materials handling injuries affect the back (lifting, repetitive motion, slips and falls), when manually transporting bulk dry materials, additional safety hazards such as poor respiratory environment and fugitive dust problems — hazards that can be effectively eliminated with pneumatic conveying systems — are present.
Pneumatic conveyors use vacuum to gently and quickly move materials from point to point with nothing in the way to impede the efficiency of its movement. Used to convey, batch, and weigh dry materials from fine powders to plastic pellets and caps, pneumatic conveyors consist of five basic pieces of equipment that come together to work as one – a pick up point, convey tubing, a vacuum receiver, a vacuum producer and a control module.
From simple systems that semi-automate a process to more sophisticated systems that offer complete automation, improved safety always enters the equation when utilizing a pneumatic conveying system. While there is no single equation to determine the return on investment (ROI) that fits all organizations engineering out a safety hazard, data does exist to help determine how pneumatic conveyors contribute to the bottom line in terms of reduced or eliminated hazards, and gains in productivity.
OSHA’s $afety Pays (SP) worksheet calculates costs associated with specific injuries and includes a dollar amount of additional sales (and increased production) needed to cover those costs. Also, it can assist managers in quantifying the benefits of reducing or eliminating hazards when implementing a pneumatic conveying system.
One of the most effective methods to justify costs of ergonomic improvements is through production enhancements. Just shaving seconds from a single process can have a huge impact. An example from ASSE’s website, ROI of Ergonomic Improvements: Demonstrating Value to the Business, validates how shaving 3.2 seconds from a task can reduce direct labor costs by $29,000 per year.
Fall Hazards
It is not unusual for organizations to seek out pneumatic conveying solutions for the express purpose of eradicating ergonomic hazards. A common dilemma in the industrial world is the manual transport of materials to raised platforms where ingredients are dumped into hoppers. This action represents not only ergonomic hazards, but also a fall hazard. Although the majority of organizations seeking to eliminate this type of hazard have yet to experience a fall event, proactive executives seek out automated solutions to safeguard workers.
When increased demand turned up the notch on production for a particular product, a chemical manufacturer’s primary goal was to eradicate an ergonomic issue by removing the need for workers to dump 20-40 drums containing powder chemicals, that weighed up to 225 pounds each, from a raised platform. Although the company hadn’t had any injuries with that process, its policy was to wipe out any potential.
Although the job required a single operator, the organization staffed it with two people to reduce the potential for injuries. Initially, the company tried a bucket elevator. That method, however, created a lot of dust in the air and still presented an over-exertion hazard when dumping the product into the elevator. The company also considered a hoist system, but that would have required operators to do some drum handling which would have made the process significantly slower than their existing method.
The size of the pneumatic conveying system depends upon the desired speed at which product is transferred from one place to another as well as the distance between two transfer points. Because the company wanted to eliminate an ergonomic issue and timing wasn’t an issue it chose to utilize a smaller conveying system.
To move several hundred pounds of material in 30 minutes, a Tube Hopper was utilized to transfer the claylike material up a level into a volumetric feeder. Another Tube Hopper was also added to a separate line that pulled granular material from awkward shaped drums weighing over 200 pounds each, up into a liquid mixing tank.
Although the time to transfer the products stayed relatively the same with the new units, the job went from requiring two people to a single operator and eliminated a hazard. The company wasn’t looking to cut any people, but they did save some money by it and the unit paid for itself in the first year of use.
Elevated falls are less frequent but more severe than same-level falls in the workplace. In 2011, falls, slips and trips claimed the lives of 666 workers and one in four resulted from a fall of less than 10 feet.
The manufacturing industry experienced 47 of the fall fatalities in 2011. OSHA’s SP worksheet, does not include cost data for fatalities, but a 2003 mean estimate of direct costs for a single fatality in the workplace was approximately $900,000.
Direct costs are budgeted costs, or insured costs. Indirect costs are those that are not budgeted (not insured) and eat away at profits. Indirect costs are estimated to be anywhere from 2 to 20 times the direct cost. These costs include training replacement employees, accident investigation and implementation of corrective measures, lost productivity, fines and penalties, repairs, any other costs not covered by insurance, including loss of employee morale.
Fall fatalities demonstrate a worst-case scenario in the workplace and have a severe impact on employee morale, and high indirect costs that are conservative at one million dollars. Most commonly, falls, trips and slips result in back injury or some other musculoskeletal disorder (MSD); however, statistically MSDs from those hazards are calculated separately. MSDs include any injury, damage or disorder of the joints or other tissues in the upper/lower limbs or the back.
Back Injury
In the manufacturing arena, 4 out of 5 materials handling injuries affect the back and require a median of 10 days for workers to recuperate. Using the $afety Pays worksheet, calculating with a 5 percent profit margin, a strain has indirect costs in excess of $33,000 and requires an additional $672,122 in sales to recoup those costs. Anytime organizations can eliminate the possibility of back injuries, injury costs should be taken into consideration when determining ROI.
While working on a major efficiency project that culminated in the building of new rooms for a blending area, a tea manufacturer wanted to also cut down the amount of lifting that the operators were doing manually in the production department.
Previously, the operators were manually weighing individual hundred-pound batches into barrels, using forklifts to transfer them to the top level, and then dumping them into hoppers by hand.
One of the biggest concerns for the tea manufacturer was the breakdown of the materials themselves. Pneumatic conveying is a very gentle way to move product and once that was proven to the manufacturer in a testing facility; the system was designed to automate the process.
Now rather than operators using forklifts to bring barrels up to the mezzanine level, and manually scooping materials into the hopper, operators insert a wand into the barrels and product is pneumatically transferred from the wand to the blenders, eliminating all the forklift traffic and wear and tear of the workers’ backs.
In addition to eliminating ergonomic issues and potential costs associated with injury, the company had a 20 percent increase in productivity.
Fugitive Dust Control
Pneumatic conveying systems are fully enclosed, protecting materials from air, dirt and waste. Because product does not escape from a pneumatic conveying system, particulates that can endanger workers respiratory health or settle on equipment and surfaces posing an explosion hazard are prevented from entering the environment.
Any time a pneumatic conveying system is employed, costs associated with housekeeping diminish as well as the potential for a dust explosion. Much could be written about combustible dust explosions and the benefits of pneumatic conveying systems; however, it should be made clear that the cost of employing even the most sophisticated pneumatic conveying system would be far less than that of a dust explosion.
Since the inherent nature of the pneumatic system prevents loose powder from becoming airborne, it makes for a cleaner and safer environment all around, and a greater number of organizations are looking at safety reasons for engaging a pneumatic conveying system.
Several years ago, a manufacturer of cable faced a major materials handling problem--two of the fourteen ingredients used in its process were toxic. The ingredients were received in powder form in 50-lb bags which were opened on the production floor, hatched on platform scales and manually dumped into a mixer or blender. Despite extensive use of exhaust ducting and respiratory protection for the workers in the area, engineers were still concerned with the impact of toxic contamination on the environment and the threat of not meeting OSHA regulatory standards.
Indirect costs for a single dust disease, according the SP worksheet, are around 25,000 with an additional $509,000 needed in sales to recoup the cost. The worksheet lists other respiratory illnesses as well as illnesses associated that can be caused by dusty environments such as dermatitis. A single injury for dermatitis can result in indirect costs around $10,000 with over $200,000 of additional sales to make up for those costs.
The cable company eliminated the need to dump 50-pound bags of toxic material into a mixer manually by converting to a monorail-mounted hoist. The device lifts and positions semi-bulk bags to an unloader, which forms a dust-tight seal against the ring on the discharge opening. Agitator pads and an auger under the storage bin help to deliver material into a weigh hopper on the floor below at a controlled rate. The material is then conveyed to a blender on an upper floor.
The entire flow path is enclosed resulting in a safer environment and because of the bulk packaging, the cost per pound of materials is lower. In addition, handling costs in receiving, storing and discharging the materials are substantially lower.
Manual materials handling is the number one source of compensable injuries in the manufacturing sector. Many of those injuries could be avoided by employing a pneumatic conveying system —
often for less than combined direct and indirect costs associated with those injuries. Nearly 100 percent of the time, solving a workplace hazard with a pneumatic conveyor system increases profit through production efficiencies.
This article originally appeared in the July/August 2024 issue of Occupational Health & Safety.