Ergonomic interventions at Unimin

W.L. Porter and A.G. Mayton

Research engineer and lead research engineer, respectively, National Institute for 

Occupational Safety and Health (NIOSH), Pittsburgh, Pennsylvania

A. O’Brien

General manager, Safety and Health, Unimin Corporation, Winchester, Virginia

Abstract

In 2004, management at Unimin’s Gleason, Tennessee, operation began implementing ergonomic interventions specifically targeted to reduce the risk of musculoskeletal injuries (MSIs). Together with 

corporate and site management, Unimin identified worksite hazards and began to modify work practices 

and equipment. Some interventions were relatively simple and were implemented immediately. Others, 

such as improvements to a mobile shredder, were more complex but were eventually resolved through a 

participatory approach with employees, management, manufacturers and NIOSH. This paper discusses 

ergonomic interventions that were successfully implemented using a participatory approach to reducing 

the risk of injury.

Introduction

Unimin is an industrial minerals mining company with more 

than 100 operations worldwide. Unimin produces ball clay, 

silica, kaolin clay, dolomite, nepheline syenite and olivine. The 

Gleason, Tennessee, site is a ball clay surface mining facility 

and a processing facility. Ball clay is a product used mostly 

for ceramic fixtures and as a bonding agent in ceramic ware. 

When compared to many other Unimin mines, the Gleason site 

was experiencing a higher percentage of MSIs (categorized 

as sprains and strain injuries in an injury database generated 

by Unimin) for the period of 2000 through 2006. During that 

period, MSIs accounted for 44% of all reported incidents at 

Gleason, compared to 26% for all of Unimin. The management 

team at Gleason continuously searched for means to improve 

the working environment. To identify improvements that would 

have the most dramatic impact on MSIs, the management team 

approached miners individually and discussed their concerns 

and thoughts on work practices that required significant physical exertion or were repetitive. 

While a more formal program of integrating an ergonomics program was available to Unimin, the company chose to 

implement specific training related to their concerns with an 

aging workforce. This specific training was given to Unimin’s 

Gleason mine safety and health supervisor by NIOSH researchers. The “Age Awareness Training,” described below, was then 

given to the workforce at biweekly safety meetings until all 

the modules were addressed. The goal was to empower the 

employees with knowledge, understanding and application 

of principles related to reducing musculoskeletal injuries in 

the workplace. This resulted in ergonomic principles being 

incorporated into the established safety processes at Gleason. 

Under the guidance of NIOSH researchers several significant 

interventions were successfully implemented, which are described in the next section. The training itself was a successful 

intervention. The goal of this collaboration was to develop 

interventions to reduce the likelihood of injuries resulting from 

awkward postures or excessive forces.

Intervention process

While NIOSH researchers visited two Unimin sites prior to 

implementing the training, several jobs were observed for work 

related musculoskeletal risk factors. These jobs or tasks were 

identified by NIOSH and Unimin safety officials as physically 

challenging, most likely contributing to cumulative injury and/or 

affecting a large number of employees. An analysis of injuries 

obtained through the Mine Safety and Health Administration 

(MSHA) injury database revealed that greater than 40% of the 

Gleason site’s injuries were cumulative in nature. Unimin was 

interested in redesigning or eliminating those tasks that were 

contributing to these injuries. These improvements served as a 

catalyst for motivating employees to make additional changes 

when the training was introduced. For each of the following 

interventions, a systematic process was used. 

A similar process was successfully used in the work documented by Torma-Krajewski et al. (2007). The general process 

was to determine which part or parts were contributing the most 

to the risk of injury, involve the workers in the discovery and 

solution brainstorming process, redesign the task/equipment, 
implement the intervention, evaluate the intervention for its 

ability to reduce risk factors while minimizing introduction of 

new risk factors, and sharing success with other Unimin sites. 

The choice to implement a solution was determined based on 

worker injury and discomfort reports, number of employees 

affected, ease and cost of solution and timeliness. A solution 

was considered successful if it reduced the associated risk 

factors, eliminated that portion of the task, was accepted and 

determined successful by employees or if it resulted in reduced 

injuries. While in many cases it may take several years to see 

injury rate reductions, Unimin reported reductions in injury 

rate for this site after 18 months. Evaluation of the job post 

intervention was the immediate measure of the success in 

reducing injury risk factors such as awkward postures, forceful exertions, repetition and vibration. The following section 

summarizes each intervention including a brief description of 

the task and intervention discovery process.

Figure 1 — Mineworker demonstrates power connection.

Figure 2 — The rubber “boot” to protect the male cable 

connector from dirt, dust and damage. 

Interventions

Shredder power cable connector. Due to the nature of ball 

clay, some unusual equipment is required to process it, such 

as a clay shredder, which shreds raw clay and disperses it onto 

a stockpile. The shredders used at Gleason are mobile and, on 

average, are moved twice daily using a front-end loader. Each 

time the shredder is moved it must be connected/disconnected 

to a power source. Because the connector weighs 9 kg (20 

lbs) and is difficult to handle, forceful exertions and awkward 

postures occur when performing this task. 

During discussions with the employees, Gleason mine 

management became aware of difficulties in connecting and 

disconnecting the shredder power cable (Fig. 1). Issues of 

concern included:

• the aluminum sleeve became bent, which made it difficult 

to connect and disconnect from the receptacle;

• hardened and built-up clay on the connectors made it 

difficult to insert into the receptacle;

• dust on the aluminum sleeve made it more difficult to 

connect; and

• awkward postures (rounded back, arm position with 

respect to the body and standing on uneven ground) 

occurred when connecting and disconnecting the cable 

to the power source. 

Based on the above issues, a possible solution of using 

an off-the-shelf cable connector was considered. Features of 

this connector were its light weight, 2.4 kg (5.2 lbs), and its 

ability to form an easier connection — it had concealed components that remained hidden until the connection was made, 

which kept the male end free of dirt and debris. The connector also eliminated arc flash exposure and had an accessory 

tool especially designed to aid in connecting/disconnecting. 

A significant capital investment was needed to purchase the 

male/female connectors and the accessory tool and to install 

all related equipment. 

Mine management obtained a sample of the parts necessary 

for installing the new connector from an equipment vendor. 

They, in turn, asked nearby mines regarding any experience 

their operations had in using this type of connectors. The feedback received from the other operations was negative — the 

external recessed areas of the connectors became clogged with 

clay particles, and if excessive force was used when making 

a connection, parts of the connector easily bent. Based on this 

feedback and a potential capital investment of more than $11,000, 

the mine management rejected the new connector option. 

Subsequently, mine management came up with other options in conjunction with maintenance personnel and shredder 

operators. This resulted in the following actions: 

• A rubber boot (Fig. 2) for the aluminum sleeve was 

installed on the male end to prevent the sleeve from 

bending and to keep it clean. The rubber boot was made 

from a protective cover for a dust collector cartridge that 

the mine normally stocks.

• An electric grinder was used to file burrs on the inside 

of the connectors to make insertion of the plug easier.

• A spray lubricant, commonly known as “Super Slick,” 

was applied to the contacts and sleeve of the connector 

to reduce friction when inserting the connector into the 

receptacle.

The shredder power cable connector intervention is summarized in Table 1. The Gleason mine safety and health supervisor 
estimated the cost of this intervention as $500 in materials and 

worker hours. The supervisor indicated that the “employees 

liked the results” and described the intervention process and 

outcome as “very good.”

Cable handling. Another issue associated with the shredder 

was how to minimize injury risk when handling the power 

cable. The specific components of this task included unraveling 

the cable from its storage device, holding the connector and 

dragging the cable to and from the power source receptacle 

and then placing the cable back on the machine in preparation 

for another move. 

Initially, a mechanized cable reel was considered as an 

option to reduce the physical cable handling. A cable reel 

manufacturer was enlisted to assist with this option. Given 

the available space to mount the reel within the frame of the 

shredder, an initial design was developed and supplied to mine 

management. One major limitation of the power reel was that, 

although it provided cable retrieval capability, employees 

would still have to pull the cable off the reel to connect it to 

the power source. Also, an estimated cost of the power reel 

solution for four shredder machines exceeded $38,000. After 

considering the limitations and costs of the power cable reel, 

mine management rejected this option. 

Afterwards, the mine management team considered a lowcost and simple solution to the cable-handling issue offered 

by an off-shift shredder operator who was listening to the 

conversation between the NIOSH researchers and a fellow 

operator. This involved a procedural change to cable handling 

that constituted a method of looping the cable in 3-m (10-ft) 

lengths (as seen in Fig. 3b), so that only a 3-m (10-ft) length of 

cable is handled at a time instead of a haphazardly overlapping 

bundle. NIOSH researchers determined that overlapping the 

cable (as seen in Fig. 3a) while unwinding it increased the force 

required by approximately one third, i.e., mean forces for small 

drag at 82.3 N (18.5 pound-force) with no cable overlap versus 

113 N (25.5 pound-force) needed when overlapped cable. 

This intervention, including training for all workers, was 

implemented by Gleason Mine management quickly and at no 

cost. The Gleason mine safety and health supervisor stated that 

this intervention “was a good partial solution” and was accepted 

fairly well, although a few operators still try to “manhandle” 

the cable. This solution, even though not optimal as yet, helped 

to reduce the amount of load handled by 28% and raised the 

awareness of the employees while a more cost-effective solution can be further explored. Table 2 presents a summary of 

the cable handling target task.

Primary risk factors

• Forceful exertions. 

• Awkward postures, in particular, a rounded-back arm

position with respect to the body and standing on 

uneven ground.

Root cause

 Connector becomes dirty and bent, which increases 

 the difficulty plugging and unplugging the connectors.

Improvement description

• Added a rubber boot to the aluminum sleeve to keep

it clean and prevent bending. 

• An electric grinder was used to file burrs on the inside

of the connectors to make insertion of the plug easier.

• A spray lubricant was applied to the contacts and

sleeve of the connector to reduce friction when

inserting the connector receptacle.

Table 1 — Target task: Shredder power cable connector.

Figure 3a — Shredder cable haphazardly overlapped.

Figure 3b — Shredder cable evenly looped.

Cleaning and maintaining tub. A third intervention concerning 

the shredder was for the “tub,” which requires regular cleaning 

and maintenance. As above, issues were identified as a result 

of feedback from the shredder operators. Injury risk factors 

for this task included awkward postures while climbing into 

or leaning over the side of the tub to remove large pieces of 

rock. Before the intervention, employees would climb over 

the side of the tub to clean it out, to change knives and to 

remove large pieces of rock and clay. This placed employees 

in postures that could lead to back and shoulder strains. The 

tub has a diameter of 1.6 m (62 in.) and is 1.4 m (55 in.) high 

(measured from the base inside the tub). Considering that half 

the male population and 95% of the female population have a 

shoulder height of less than 1.4 m (56 in.), the tub height posed 
a significant barrier. Both men and women would have to lean 

over the rim of the tub to retrieve rocks, typically weighing 

23 to 27 kg (50 to 60 lbs) and then throw them over the tub 

at shoulder height. Mine management was concerned about 

workers’ safety and the potential musculoskeletal injury risks 

when climbing in and out of the tub, leaning over the tub wall 

and lifting rocks out of the tub. 

A team consisting of mine management, maintenance personnel and shredder operators conducted intensive brainstorming 

sessions to reach a low-cost effective solution. It resulted in 

cutting the tub to create a hinged door (Figs. 4a and 4b). This 

intervention demonstrated the following benefits:

• It reduced the risk factors associated with leaning over 

the side and climbing over the side of the tub. The worker 

was now able to walk into the tub to perform cleaning 

or maintenance duties.

• It reduced the injury risk associated with lifting heavy 

rocks to shoulder height and above to throw them over 

the top of the tub side. Instead workers are able to use 

the door of the tub to easily slide out rocks and debris.

• It allowed operators to safely carry maintenance tools 

into and out of the tub. 

The cleaning and maintaining tub target task is summarized 

in Table 3. The Gleason mine safety and health supervisor 

estimated $1,200 as the total cost of this intervention for all 

three shredders. The supervisor said, “This intervention has 

been very well accepted. The process of brainstorming by the 

maintenance department and shredder operators...[with] the 

solutions reached by the parties involved was good. This was 

a remarkably simple, but very worthwhile intervention.”

Figure 4a — Shredder tub with door installed.

Figure 4b — Worker easily removing large rocks when 

using door.

Primary risk factors

Primary risk factors

• Awkward postures. 

• Contact stresses while climbing into or leaning over

 the side of the tub.

• Forceful exertions while trying to remove large

 pieces of rock. 

Root cause

 Lack of acces to tub interior.

Improvement description

 Added a hinged door by cutting the side of the tub.

Table 3 — Target task: Cleaning and maintaining tub.

Handling sodium silicate. Another task that was improved 

as a result of the NIOSH-Unimin collaboration was the handling of a clay additive, sodium silicate. The sodium silicate 

is added in 23 kg (50 lb) increments to the ball clay slurry up 

to three times a day. Originally the additive was dispensed 

into a bucket and then carried along a catwalk for about 15 

m (50 ft) (Fig. 5a). This catwalk was very narrow and forced 

workers to carry the bucket one handed in front of or behind 

their body or to walk sideways. 

NIOSH researchers recommended extending the piping 

for the additive over to its destination to eliminate carrying 

the load. As shown in Fig. 5b, it would still be necessary to 

pour the additive into the slurry by bucket, but workers would 

no longer carry it 15 m (50 ft). The cost of implementing the 

intervention was approximately $300. The installation was 

straightforward because the additive was already piped. They 

simply added a pump and lengthened the pipe. The employees 

liked the idea and quickly put it in place. 
The implementation of this intervention eliminated carrying 

the heavy load using awkward postures. The result is a reduction of the risk of sprain and strain injuries to the back and 

shoulders. Adding a hose with a metered valve to deliver the 

additive directly without any manual handling could enhance 

this intervention even further. Table 4 summarizes the handling 

sodium silicate target task.

Table 4 — Target task: Handling sodium silicate

Primary risk factors

• Forceful exertions. 

• Awkward postures while handling heavy and 

 awkward materials.

Root cause

 Station and catwalk were not setup to directly add the 

 additive. The additive has to be manually carried and 

 added.

Improvement description

 Extended the additive dispensing pipe to the delivery 

 point to eliminate carrying the load. It is still necessary 

 to pour the additive into the slurry by bucket.

Figure 5a — Pre-intervention handling and carrying of the 

bucket (arrow depicts walking path).

Figure 5b — Post-intervention filling of the bucket (occurs 

at end of path way shown in Fig. 5a).

Age Awareness Training. Age Awareness Training (AAT) 

was developed by NIOSH in response to the concern that an 

increasing number of older mine workers are remaining on 

the job. The training discusses normal age-related changes 

that have the potential to affect worker health and safety. Also 

addressed by the AAT is how these normal changes can be 

mediated through modifications to the workplace or improvements to personal health behaviors. The AAT includes seven 

training modules covering topics such as hearing, vision and 

the musculoskeletal system. 

During the collaboration it was determined that at the Gleason 

facility the median age was 45.5 (range 22 to 68) years and the 

median length of mining experience was 19.5 (range 0 to 40) 

years. This diversity of the workforce led to a decision to use 

Gleason as a field test location for the AAT during the summer 

and fall of 2006. The first “kick off” module (Introduction) 

was given at the start of a monthly safety meeting to about 60 

employees and was followed with biweekly safety talks on 

each of the modules. Educating workers on issues related to 

the physical and cognitive aging process can be an effective 

way to reduce the possibility of injuries. 

The Gleason mine safety and health supervisor commented: 

“Overall, the vision module (the first to be given in the biweekly 

format) was received rather well and has provoked some good 

discussion and a few projects.” For example, one intervention 

resulting from the vision module was applying antiglare film 

on the windows of the mobile equipment at the mine pit. The 

effect of glare on an aging population was identified by the 

module as: “After age 40, changes in the lens and the vitreous 

gel [of the eye] cause the resistance to glare to decline by 50% 

every 12 years.” Given that older workers may have problems 

adapting to situations with glare, adding antiglare film reduced 

the risk of injury to the workers by allowing them to be able 

to distinguish any possible hazards. 

Impact of the interventions 

Initially the workforce did not readily accept ergonomics and 

the application of its principles at Gleason. However, employee 

buy-in was generated through training and employee involvement in developing the interventions. The workers became 

more proactive about problem solving and developed and 

implemented many of the interventions discussed above with 

little guidance after the initial discussion of ergonomics principles. For the nine-month period from Jan. 1, 2006, through 

Sept. 30, 2006, there has been only a single MSI reported as 

compared to the yearly average of approximately four MSIs 

(for the period of 2000 through 2005). This decrease in MSIs 

cannot directly be attributed to the interventions, but it may 

be due to increased awareness of the employees about risk 

factors. There has also been a noted reduction in the average 

modified duty days per MSI of approximately 23%. This 

reduction in modified duty days has resulted in an estimated 

savings to Gleason of approximately $14,000 in 2006. As the 

age awareness training proceeds and the application of ergonomic principles becomes part of the mine’s culture, additional 

interventions are expected to be implemented at Gleason over 

the next few years. 
Discussion

Positive results have also been realized in other private sector ergonomics programs, including one studied by NIOSH 

(Torma-Krajewski et al., 2007) and case studies investigated 

by the U.S. General Accounting Office (GAO) (1997). TormaKrajewski et al. (2007) discussed the successful implementation 

of an ergonomics process at a western surface mine (Bridger 

Coal) over a three-year period. In a manner similar to the one 

discussed in this paper, implementing interventions through 

a participative employee-based process reduced exposure to 

ergonomic risk factors. The coordinator for the ergonomics 

process at Bridger Coal stated: “Ergonomics has played an 

important role in helping Bridger Coal reach our goal of providing the safest and healthiest working environment possible 

for our employees.... The Ergonomics Program is currently an 

integral part of our company and we are confident that it will 

continue to improve and enhance the safe working experience 

at our mine.”

Moreover, GAO (1997) conducted case studies involving 

five U.S. companies with staffs ranging from 300 to 5,300 

employees. The GAO reported that officials at all the facilities 

believed their ergonomics programs yielded benefits, including reduction in workers’ compensation costs associated with 

MSIs. The case studies also showed reductions in overall 

injuries and illnesses as well as in the number of days injured 

employees were out of work and increased worker morale 

and productivity. The conclusion of the GAO report was “...

that positive results can be achieved through an approach 

incorporating certain core elements that are implemented in a 

simple, informal, site-specific manner.”

Conclusions

Several ergonomic interventions implemented at Unimin’s 

Gleason mine reduced or eliminated a number of risk factors 

that could lead to injuries. By reengineering the existing safety 

processes to include the application of ergonomic principles, cost 

effective interventions were quickly and easily developed by the 

workers themselves. These efforts also laid the foundation for 

future interventions and a better understanding of the types of 

activities and designs that lead to decreased exposure to these 

risk factors. The success of the interventions described stemmed 

from its participatory approach to problem solving; empowering 

all personnel with a voice in health and safety issues. The success achieved at the Unimin Gleason mine is also corroborated 

by results documented in the NIOSH and GAO studies cited 

previously (Torma-Krajewski et al., 2007; GAO, 1997).

Acknowledgments

The authors acknowledge the contributions by the following 

individuals involved in the implementation of interventions 

at Gleason, Tennessee: Diana Schwerha, formerly of NIOSH 

and now with Ohio University; Mary Ellen Nelson and Al 

Brautigam of NIOSH; Bob Newman and Phil Boyd of Gleason 

mine management; and the employees at the Gleason plant. 

The authors would also like to acknowledge the technical 

contributions by Lisa Steiner.

Disclaimer

The findings and conclusions in this report are those of the 

authors and do not necessarily represent the views of the National Institute for Occupational Safety and Health.

References

Torma-Krajewski, J., Steiner, L., Lewis, P., Gust, P., and Johnson, K., 2007, 

“Implementation of an ergonomics process at a U.S. surface coal mine,” 

International Journal of Industrial Ergonomics, Vol. 37, pp. 157-167.

U.S. Government Accounting Office (GAO), 1997, “Worker Protection: Private 

Sector Ergonomics Programs Yield Positive Results,” GAO/HEHS-97-163, 

pp.137.