P

r 2007 41

manuscript submitted online January 2007. revised manuscript 

accepted for publication September 2007. discussion of this 

peer-reviewed and approved paper is invited and must be 

submitted to Sme Publications dept. prior to march 31, 2008. 

Back injury control measures for 


manual lifting and seat design
 

S. gallagher and a.g. mayton 

S. Gallagher and A.G. Mayton are senior research 

scientist and lead research scientist, respectively, with nIoSh, 

Pittsburgh, Pennsylvania. Paper number tP-07-003. original 

Abstract 

Back injuries account for a high proportion of lost workdays in the mining industry and are a leading cause of 

disability in mine workers. Two risk factors for low back 

injuries are manual lifting and whole-body vibration exposure when operating mobile equipment. Recent research 

has shed light on possible mechanisms through which low 

back injuries may occur, and the results of these studies can 

be used to improve the design of lifting tasks and seats to 

decrease injury risk. This article discusses recent research 

results and how this knowledge can be leveraged to reduce 

the risk of low back pain. 

Introduction 

The mining industry has long 

been associated with a high incidence of low back disorders and pain 

(Klein et al., 1984; Leigh and Sheetz, 

1989; Brinckmann et al., 1998). It is 

believed that the higher incidence of 

these injuries among miners is the 

result of high exposures to postural 

demands, heavy manual work and 

exposure to whole-body vibration (WBV). Recent work 

indicated that miners involved with heavy lifting (especially in restricted spaces or on uneven ground) or who 

have been exposed to whole-body vibration in undamped 

seats experience noticeable changes in their spines, consistent with degeneration of the intervetebral discs of the 

spine (Brinckmann et al., 1998).As described here, there 

is increasing evidence that disc degeneration plays a large 

role in the development of low back pain, particularly 

chronic back pain. 

Figure 1 shows the rate of back injuries for various 

industrial sectors in the United States from 1992 through 

2001 (NIOSH, 2004). One can see a general decline in the 

rate of back injuries for all sectors over this timeframe. 

During the first half of this period, mining was typically 

the fourth highest sector (out of nine) in terms of back 

injury rate. During the latter half of the period, mining 

shows some improvement in relation to other industry 

sectors and was among the lowest sectors in terms of 

back injury rate in 2001. However, it should be noted that 

mining was the third highest sector in the preceding year. 

Clearly, some improvement can be seen over this time 

period. However, back injuries remain a leading cause 

of lost time and represent a tremendous cost to the U.S. 

mining industry. 

Back injuries are also a significant international issue in mining. 

In Australia, for example, workers 

compensation statistics for the state 

of New South Wales from 1998 to 

1999 found that 30 percent of all 

workplace injury claims involved the 

back. The mining industry was the 

second worst industry in terms of 

incidence of male back injury, with 

40.6 claims per 1,000 wage and salary earners (Stewart 

et al., 2003). Back injury rates among miners in Scotland 

(Lloyd et al., 1986) and degenerative changes to the spine 

in German coal and salt miners (Brinckmann et al., 1998) 

have all been found significantly elevated with respect 

to comparison populations. These statistics highlight the 

need for solutions to reduce back injury risk in the mining industry to better control costs and reduce disability 

among mine workers. 

Causes of back pain 

Until recently, medical doctors generally assumed that 

back pain was the result of muscle strain, ligament pain 

or so-called “trigger points” (Bogduk, 1997). However, 

research supporting these mechanisms of pain has been 

scant. There are three mechanisms that have shown high 

associations with back pain in controlled scientific studies: 

•	 sacroiliac pain (present in 13 percent of back 

pain sufferers) (Maigne et al., 1996), 

•	 facet joint pain (present in 15 percent of back 

pain sufferers) (Schwarzer et al., 1994) and 

•	 disc disruption and degeneration (present in 

39 percent of chronic back pain sufferers) 

 (Moneta et al., 1994). 

The latter mechanism, which bears the highest relationship to back pain that has yet been shown, will be the 

focus of this section. 

Scientists now believe they know how back pain may 

develop in cases involving disc disruption and degeneration (Bogduk, 1997). When the spine experiences a 

sufficient load, the first structure to fail is the vertebral 

endplate, a structure that attaches the disc of the spine to 

the vertebral body and that is important in disc nutrition 

(Fig. 2). The body’s response to the fracture is to attempt 

to heal the fracture by “mortaring” the fracture with scar 

tissue. Unfortunately, the scar tissue impedes the flow of 

nutrition to the disc itself (discs are dependent on nutrition from blood vessels in the vertebral bones), and if 
the supply is reduced sufficiently, the disc will start to degenerate. As this degeneration process proceeds, fissures 

or tears in the fibers of the disc start to develop from the 

inside out. If any of these tears is a Grade 3 fissure (Fig. 

3), an inflammatory response occurs in the disc, which 

will lead to the well-known sensation of low back pain 

(Peng, 2006). 

The best approach to preventing this degenerative 

process would appear to be minimizing the likelihood of 

the initial endplate fracture. Endplate fractures can occur 

in two ways. The first is that the endplate’s strength may 

be exceeded by one very large load placed on the spine. 

Figure 1	 

Back injury rates for major United States industrial sectors, 1992-2001. 

Figure 2 

Disc degeneration is thought to be initiated with an 

endplate fracture, which inhibits disc nutrition leading 

to disc degeneration (Bogduk, 1997). 

This may occur in the case of a fall or 

an extreme jolt when riding in a vehicle. However, most experts believe 

that endplate fractures may occur 

more commonly due to fatigue failure. 

In this process, a load (perhaps when 

lifting) will result in a small fracture in 

the endplate. Subsequent loading (e.g., 

repeated lifting) will cause this small 

fracture to expand, ultimately leading to a full-fledged fracture. In this 

way, repeated sub-maximal loading 

can lead to an injury that is equivalent to an injury experienced in a onetime overload of the tissue strength 

(Brinckmann et al., 1988; Gallagher 

et al., 2005). 

An important implication of the 

effect of repetitive loading is that people can be performing tasks that they 

believe are safe, such as lifting a 23-kg 

(50-lb) bag, because they have done 

so before without pain, but in reality 

each lift may be leading to a slight amount of damage. 

The resulting accumulation of weakness in the spine may 

lead to an injury that may result from what seems like a 

fairly innocuous task (such as bending down to pick up 

a pencil), but which is really the result of damage that 

has accumulated over time. Two things that can result 

in such repetitive spine loading are manual lifting and 

exposure to whole-body vibration. The purpose of this 

paper is to describe methods by which the risks of back 

injury may be reduced in the mining industry for workers 

so exposed. 

Controlling low back risks associated

with handling materials 

A comprehensive approach is needed to reduce the 

risks associated with back pain resulting from handling 

materials. This approach includes factors such as proper 

layout of facilities and supply handling systems, development and/or use of appropriate equipment or aids and, 

when manual lifting is necessary, proper design of lifting 

tasks. Harsh mining environments can sometimes make 

aspects of this approach difficult to implement. However, 

there are usually methods that can be used to improve 

the design of supply handling systems at any mine site. 

Facilities layout. Transportation of materials is costly 

in terms of space, machinery and energy. It does not add 

value to the object being moved and it exposes workers 

to numerous hazards. In fact, given that transportation 

costs for materials typically account for 30 percent to 

75 percent of the total operating cost, there is a strong 

economic incentive to improve the efficiency of materials 

handling systems (Kroemer, 1997). However, some may 

view the reduction of risk to the workers by redesigning, 

improving or eliminating transportation barriers to be a 

more compelling motivation. Fortunately, ergonomic design of materials handling systems can benefit the health 

of the worker and the bottom line. 

Efficient material flow is associated with few transportation moves, whether on the surface or underground. 

Analysis of current materials handling practices is a criti­
cal step in the proper design of existing and planned facilities. When existing facilities are present, it is often 

difficult to change the building or the layout. However, 

improvements in material flow can often be realized. It is 

more efficient to design new facilities for the ergonomically best transport than trying to improve a design that is 

faulty (Kroemer, 1997). For this reason, it is important to 

include an ergonomist in the team planning the construction of a new facility. 

Figure 3 

Grade 3 disc fissures have been strongly associated with 

chronic low back pain (Bogduk 1997). 

For existing facilities, generalized checklists have 

been developed that can help identify problem areas for 

typical materials handling operations. Problem areas may 

include (Kulwiec, 1985): 

•	 crowded operating conditions, 

•	 cluttered entries and supply areas, 

•	 poor housekeeping, 

• delays or backtracking in the flow of material, 

• obstacles in the flow of materials, 

•	 manual handling of loads weighing more than 

20 kg (45 lb), 

•	 excessive storage times for materials, 

•	 single items being handled as opposed to unit 

loads, 

•	 underutilizing materials handling equipment 

where appropriate, 

•	 excessive time required to retrieve stored parts 

or supplies and 

•	 multiple handling of the same item. 

It is often helpful to describe the flow of materials 

using a diagram or flowchart that shows the sequence 

and location of materials handling activities or that 

represents a listing or table of steps associated with 

movement of a specific material (Gallagher et al., 1990; 

Kirwan and Ainsworth, 1992). This type of analysis can 

be helpful in identifying unnecessary materials handling 

activities and other inefficiencies associated with the 

supply handling system. An example is shown in Fig. 4. 

Figure 4 

Example of flowcharting of materials handling practices for concrete blocks at two mines. The procedure at Mine A 

involves more steps and several manual transfers of the block, which are inefficient and hazardous to the worker. Mine B 

accomplishes the delivery of block in fewer steps and entirely by mechanical means. 

Obviously, such an analysis has the potential to reduce 

unnecessary manual materials handling, which, in turn, 

will reduce the repetitive loading on the spine that leads 

to low back pain. 

Use and development of mechanical-assist

devices 

Use of hoists for materials handling. One technique 

that has met with considerable success in the mining 

environment is the implementation of standard hoist 

mechanisms (in the mine and on the surface) to assist 

with handling timber, track and other bulky materials, as 

shown in Fig. 5. Several mines have reported that installing hoists at central destination and delivery points can 

eliminate a significant amount of manual handling of 

heavy objects (Selan et al., 1997). 

Development of specialized vehicles. Another technique that mines have had success with is in the devel-
o p m e n t o f 

v e h i c l e s t o 

perform specialized functions. In many 

c a s e s, s u c h 

vehicles have 

been built entirely out of 

salvaged parts 

and supplies, 

making these 

solutions quite 

c o s t - e f f e c ­

tive. Figure 6 

shows a materials-handling 

cart called the 

“Zipmobile” 

(named after 

the miner who 

d e v e l o p e d 

it). This cart 

rides on the 

handrails of 

the longwall 

conveyor and 

transports supplies along the 

longwall face. 

I n s t e a d o f 

manually moving supplies beneath the longwall shields, 

miners can simply load up the cart and pull the supplies 

down the longwall face (Selan et al., 1997). 

Another example of a specialized mining application 

is the belt car shown in Fig. 7. The belt car was made 

from a recovered supply car, but it was modified to allow it to carry a 150-m (500-ft) roll of conveyor belt.The 

modifications consisted of cutting a hole in the bottom 

of the car (to allow for a larger roll of belt) and installing a pair of stanchions to hold the roll. Using this cart 

allowed the mine to have a roll of belt mechanically 

loaded on the car, which could then be driven next to 

the tailpiece. This allowed miners to splice 150 m (500 

ft) of belt without having to do any manual handling of 

the belt other than pulling it off of the roll to perform 

the splice. 

Figure 5	 

Installing hoists at central destination 

and delivery points can eliminate a 

significant amount of manual handling. 

Developing specialized mining tools. One problem 

identified by many mines is that there are a limited number of tools specifically designed for mining tasks. To 

address this problem, several mines have made efforts to 

develop in-house tools for specific mining applications. 

Figure 8 shows an example of a tool used to help remove 

conveyor belt rollers.This tool, which has a two-handed 

handle on one end and a prong that fits into a hole on 

the belt roller on the other end, provides leverage to 

facilitate the removal or installation of belt rollers and 

prevents the miner from directly handling the roller 

(which can get quite hot). Many other tools have been 

developed for mining applications. These tools largely 

rely on innovative ideas developed by miners familiar 

with the demands of the jobs they perform everyday 

(Selan et al., 1997). It should be clear that many opportunities exist for reducing the physical demands of mine 

workers through development, adaptation or use of mechanical-assist devices in the mining environment. 

Design of lifting tasks 

When the manual handling of materials cannot be eliminated through more efficient system design or through the 

use of appropriate mechanical assist devices, it is often 

possible to reduce the demands associated with manual 

lifting through appropriate design of lifting tasks. Unfortunately, manual lifting tasks are often considered unavoidable, and thus, not much thought is put into principles that 

can significantly decrease the load on the low back. However, there are some fairly straightforward design criteria 

that can reduce the loads experienced by workers during 

lifting tasks. The following sections briefly describe some 

principles that can help this goal. 

Reduce the moment. A moment of inertia (or moment) acting about the spine is defined as a force (e.g., 

the weight of a lifted object) times the distance from the 

spine to the object’s center. This distance has a multiplying effect on the force requirements of lifting a load.Thus, 

an 11 kg (25 lb) load being held 0.9 m (3 ft) away from 

the body will result in approximately twice the moment 

about the spine than a 18 kg (40 lb) load held just 0.3 m (1 

ft) in front of the body (Fig. 9). In this way, lighter weights 

can actually cause greater low back stress than heavier 

loads. Recent research has shown that the load moment 

(the weight of an object multiplied by its distance to the 

spine) is one of the best predictors of the likelihood that 

someone will experience a low back injury (Marras et al., 

1999). This means that not only can reducing the weight 

of an object decrease spinal stress, but reducing the horizontal distance to the load being lifted plays a vital role 

as well. Some ways of reducing the distance to the center of the load include eliminating physical barriers that 

prevent the worker from getting close to the load, pulling 

objects close to the body before lifting and reducing the 

size of the object. 

Reduce bending. Recent studies have shown multiple hazards related to bending the trunk forward 

when lifting. Bending forward creates an additional 

moment about the low back due to the weight of the 

torso, which the spine muscles must counteract through 

increased contraction. Spinal tissues have been found 

to fail more quickly when this additional load is imposed (Gallagher et al., 2005). In addition, it was recently found that when spine ligaments get stretched 

in sustained or repeated forward bending, the spinal 

muscles (through a feedback mechanism) actually lose 

strength and are more prone to muscle spasms (Solomonow et al., 2003). Recovery from the effects of even a 

brief period of ligament stretching can take 24 hours or 

more (Solomonow et al., 2003). While restricted spaces 

in underground mines often limit what can be done to 

limit forward bending, easier changes are often possible 

in other areas or facilities. One of the most effective 

design changes that can be made is to simply limit the 

number of items that must be manually lifted off the 

floor. Ideally, items should be stored about waist height 

and should be stored no lower than knee height and no 

higher than shoulder height. 
Figure 6 

This cart rides on the handrails of the longwall conveyor, 

facilitating movement of supplies along the longwall face. 

Figure 7 

The belt car allows miners to splice 150 m (500 ft) of belt 

without having to do any manual handling of the belt 

other than pulling it off of the roll to perform the splice. 

Seating design and whole-body

vibration (WBV) exposure 

WBV refers to mechanical energy oscillations that 

are transferred to the body as a whole, usually through 

a supporting system such as a seat or platform. Typical 

exposures in the mining industry include operation of 

equipment such as haul trucks or front-end loaders in 

surface operations and shuttle cars or mantrips in underground mines. A comprehensive NIOSH review of 

epidemiologic results concluded substantial evidence 

of an association between exposure to WBV and back 

disorders (Bernard et al., 1997). Clearly, the repeated 

bouncing and jostling of the body experienced when driving over rough haul roads can be expected to impart significant loads on the lumbar spine, which may accelerate 

the degenerative changes detailed in previous sections 

of this paper. In addition, the development of vibration 

standards (e.g., ISO 1997) demonstrates that exposure 

to WBV may negatively impact worker safety, comfort, 

working efficiency and performance. 

There are two basic types of vibration: sinusoidal and 

random. Sinusoidal vibration is characterized as a waveform that is repeatable at regular intervals. It is most often employed in laboratory studies. On the other hand, 

random vibration is irregular and unpredictable. It is the 

type of vibration most often encountered in the work 

environment (Sanders and McCormick, 1993). Furthermore, the term damping is associated with attenuation 

and is simply the dissipation of vibration energy with time 

or distance (Griffin, 1990). 

Vibration exposure can affect the human body in various ways determined by the characteristics of vibration 

that include frequency (the number of oscillations per second), magnitude (or amplitude) and duration of exposure. 

The direction of vibration (vertical, lateral and fore-aft), 

along with the mass and body part locations, also contributes to the effects of vibration exposure to the human 

body. Moreover, vibration transmitted to the human body 

can be either amplified (magnified, increased) or attenuated (reduced, lessened) according to posture, frequency 

and seating type (Sanders and McCormick, 1993). 

Different parts of the body have different natural 

frequencies (frequencies at which the structure will naturally vibrate). When an external force excites the body 

part at its natural frequency, vibration of this body part 

will occur at maximum amplitude, which is larger than 

the original vibration. This condition is called resonance 

(Sanders and McCormick, 1993). The large oscillations 

that occur create potentially harmful stresses within the 

body part. 

It is also important to consider the level or magnitude 

of vibration during WBV exposure. Reactions to various 

levels of vibration have been noted for passengers using 

public transportation: 0.32 m/s2 is not uncomfortable, 0.8 

to 1.6 m/s2 is uncomfortable and greater than 2.0 m/s2 is 

extremely uncomfortable (ISO, 1997). 

Figure 10 shows the perceived effects of WBV exposure according to various vibration frequencies. At 

different frequencies of exposure, subjects increased the 

vibration magnitude to a level that if increased further 

would surely result in damage.They responded according 

to where they sensed pain or discomfort in their bodies 

(Magid and Coermann, 1960). Back pain in this figure is 

perceived to occur between 8 to 12 Hz. Whereas, general 

discomfort of the whole body was shown to occur from 

of 4 to 9 Hz. Typically, a mine shuttle car has a natural 

frequency between 1.5 to 2.5 Hz for full-load and no-load 

conditions, which is below the frequencies of concern 

shown in Fig. 10. Nevertheless, a terrain-induced jar/jolt 

(mechanical shock) could could produce the frequency of 

a denoted part of the body part since a jar/jolt contains 

multiple frequencies. 

Thus, the repeated exposure in a vibration environment exhibiting frequencies found in Fig. 10, coupled 

with magnitudes greater than 2.0 m/s2

, should be avoided 

to reduce the potential risk for damage to the back and 

other parts of the body. 

Probably the best approach to protect against the 

health effects of whole-body vibration is to isolate the 

person from the vibrating source with an adequate suspension system, either on the seat or in the vehicle being 

operated or both (Tong et al., 1999). It should be noted 

that simply providing a seat cushion to the operator is not 

necessarily a good solution, because a soft cushion may 

not protect against WBV exposure (the person bottoms 

out) and may even amplify vibration — the ratio of output to input transmitted vibration is greater than 1. In addition, overall RMS (root-mean-square) acceleration has 

been shown to decrease with increasing cushion density 

(Gagliardi and Utt, 1993). However, proper seat design 
can play an important role in enhancing worker health 

and safety. Understanding the vibration environment is 

an important part of designing a safe, comfortable seat. 

Figure 8 

Use of this specially developed tool provides leverage 

to remove belt rollers and prevents having the miner to 

directly handle the roller. 

Seat design considerations 

Improving seated postures in mining equipment. 

Mine workers who operate heavy mining equipment or 

vehicles may assume different seated postures depending on the design of the vehicle workstation or operator 

compartment. For example, in underground low-seam 

coal mines, shuttle car operators must assume partially 

or, in some cases, fully reclining seated work postures due 

to mine environment, operational or equipment design 

constraints. These conditions have risks of worker injury 

through reduced visibility, increased fatigue from poor 

seating conditions or awkward postures and reduced 

work performance. 

On the other hand, large surface mining equipment 

provides the vehicle operator better opportunity to assume proper-seated postures. Vehicles in surface operations are generally thought to provide ample space within 

a workstation. While this may not always be the case, 

these vehicles would at least have greater vertical clearance or headspace compared to an underground vehicle 

constrained by a vehicle canopy. The increased vertical 

clearance can be used to add a seat suspension system 

that requires limited travel (or stroke) in the vertical 

direction. 

The seated posture for mine vehicle operators, particularly in the context of a vibration environment, is crucial as it defines the initial configuration of the body and 

that of the spine in particular. Kittusamy and Buchholz 

(2004) noted that two important risk factors for developing MSD in construction equipment operators are exposure to WBV and nonneutral body postures. Construction 

equipment is essentially the same as those operating at 

surface mines with some exceptions.Thus,this would also 

apply to surface mining equipment operators. 

A key objective is to ensure that vehicle operators 

have an optimum seat that includes energy absorption 

properties to minimize the risk factors from WBV exposure. A seated posture also affects the worker performance as the upper body muscles and ligaments work 

to maintain the body in the seat. Kazuhito and Hanai 

(1999) showed that during vibration exposure, a small 

change of posture (such as bending the knees or back) 

can noticeably affect the transmission of vibration energy 

to the body. 

Coltman (1983) studied increasing the effectiveness 

of energy-absorbing seats through improved design and 

qualification test criteria. Some major findings were: 

•	 measurement of spinal force and moment 

provided the most reliable means of relating 

test performance to spinal injury, 

•	 seat pan acceleration is not a good indicator of 

test severity or injury potential and 

•	 placement of the feet can significantly influence 

seat and occupant response to load on the 

occupant. 

In view of the above, important seat features should 

include adjustability and vibration attenuation features 

in three directions, adjustability of the suspension system 

to accommodate operator differences and, in particular, 

adjustability of low back support. Because designing a 

suitable and effective seat is application specific (and 

ideally requires measurements to quantify the vibration 

environment), the following are offered as general guidelines to consider: 

•	 minimize vibration transmitted to the body, 

preferably with seat attenuation capabilities in 

three directions (including a seat suspension 

primarily for vertical vibration) and energy 

 absorbing foam padding; 

•	 allow for proper spinal alignment to minimize 

disc pressure with foam padding (that provides 

comfort in addition to energy absorption) and 

with an adjustable backrest; 

•	 minimize muscle activity associated with main 

taining proper postures (the appropriate seat 

mechanisms, e.g., padding, backrest and lumbar 

support will do the work to maintain proper 

posture instead of the muscles); 

•	 maximize circulation to buttocks, thighs and 

knees with proper seat height, seat cushion 

dimensions and seat pan angle (SAE, 1988); 

•	 be adjustable for individual differences; 

•	 provide supportive cushioning or padding; 

•	 not interfere with visibility; 

•	 allow for movement of the head or other body 

parts; and 

•	 provide easy access to controls and monitors. 

Finally, the mine engineer/purchaser of new equipment or seats should consult with the equipment dealer/ 

manufacturer as to the availability of seats that include 

the above features. 

Reducing transmissibility of vibration 

Minimizing transmitted vibration through the seat to 

the vehicle operator is an important goal of mine health 

and safety researchers. This is accomplished by suspending first the vehicle, primarily at the wheel units (near the 

forcing source of the vibration) and secondarily by suspending the seat and workstation. In underground mining 

vehicles, wheel suspensions are not the norm. However, 

in larger off-road surface mining vehicles, this is often the 
case.When wheel suspension systems are neither possible 

nor practical, the next option is isolating or suspending 

the vehicle seat and, if possible, the operator cab/deck. 

For example, vibration isolators have been used on farm 

tractors for the operator cab/deck. 1,2 A properly designed 

suspension system of the vehicle and operator workstation will lessen the required level of vibration isolation 

at the vehicle seat. 

In addition, a major U.S. manufacturer of mine 

shuttles (Joy Mining Machinery) offers wheel and seat 

suspensions and NIOSH-design seats.The four-wheel independent suspension system consists of eight elastomeric struts,3 which is an available option on select shuttle car 

models (Coal News, 2005). In addition, this manufacturer 

provides the NIOSH-design seats (for low-coal models) 

and foam padding options as standard equipment on 

all new shuttle car low- and mid-coal seam models. The 

low-coal shuttle car seat includes low back support with 

an adjustable lumbar pad and easier adjustment in the 

fore-aft direction. 

Moreover, the seat design with the most efficient isolating and damping properties should include seat padding and a suspension system with optimized stiffness and 

damping parameters. Ideally, this would be accomplished 

with an active seat suspension designed to provide adaptive optimization through changes in seat stiffness and 

damping properties as a function of vibration frequency 

and level of magnitude (Amirouche et al., 1997). In turn, 

this can result in lower accelerations and power absorption of the human body and thus, lower the risk of operator injury and illness. 

Figure 9 

Low back stress in lifting is a function of the weight of 

the load times the distance to the base of the spine. A 

lighter weight object lifted at a distance (25 lb * 3 ft = 

75 ft-lbs) can create greater back stress than a heavier 

weight lifted closer to the body (40 lb * 1 ft = 40 ft-lbs). 

Unique mining issues affecting seating 

Harsh underground mining conditions make it difficult 

to design an effective and reliable seat with a reasonable 

life. Because mud and water are often present, an underground mine vehicle seat must be made to withstand this 

punishing environment. Components must be rugged 

enough to hold up under the large forces and loads that 

can be generated during operations from the coal, rock 

and other heavy equipment. Seat cover material should 

be used that features a tough vinyl material and when 

punctured, does not tear. Mayton et al. (2005) described 

such seat designs using unique viscoelastic foam padding 

on mid-coal seam and low-coal seam mine shuttle cars. 

The results of this NIOSH study showed lower energy 

absorption to the body for all of the NIOSH-designed 

shuttle car seats with unique viscoelastic foam padding. 

The padding combination best suited for the low-coal 

shuttle car (owing to constraints with vertical clearances) 

included 76-mm- (3-in.-) thick pad consisting of one 25.4­

mm (1-in.) layer of Sun-mate Pudgee (from Dynamic 

Systems Inc.) 4 set below two 25.4-mm (1-in.) layers of 

Sun-mate extra-soft. The mid-coal seam model shuttle 

car seat padding options included two 127-mm- (5-in.-) 

thick options. The first option consists of five 25.4-mm 

(1-in.) layers of Sun-mate extra-soft, and the second option consists of three 25.4-mm (1-in.) layers of Sun-mate 

extra-soft stacked below one 25.4-mm (1-in.) layer of 

Sun-mate Pudgee and a fourth 25.4-mm (1-in.) layer of 

Sun-mate extra-soft on top of the Pudgee.4 

Considering the seat cushion, operators should notice 

when the cushion cover is cracked, worn or damaged with 

padding exposed or protruding from the cover. This is a 

sign that seat cushioning needs to be repaired or replaced. 

Another indication for replacing the seat cushion or foam 

padding is when “bottoming out” occurs, which means that 

the seat is no longer supporting the vehicle operator. 

Furthermore, seats and their components installed 

on off-road heavy surface mining vehicles should also be 

designed with durability in mind. This would include the 

spring (mechanical or air), damper (shock absorber) and 

seat cover material (made from durable fabric instead of 

vinyl because vinyl causes sweating). 

Prevention and control. Attention to proper roadway 

maintenance can reduce the WBV load experienced by 

equipment and haul-truck operators and should be given 

due consideration in any program to control operator 

exposures. Moreover, the preferred approach to controlling or preventing WBV exposures and injury risk 

for the vehicle driver/operator should be engineering 

controls that emphasize workstation and job design or 

redesign (Kittusamy, 2002).Administrative controls such 

as switching out mining vehicle operators during breaks 

and lunch can also limit the WBV exposures that involve 

awkward work postures. However, controls of this sort 

should only be considered as an interim solution until 

better engineering controls are available to minimize 

injury risk to vehicle operators. 

Summary 

Low back pain remains a significant and costly problem 

in the mining industry. Research indicates that disc degeneration resulting from endplate fractures may be a common 

cause of pain. Prevention of endplate fractures requires reducing the loads experienced by the spine due to lifting and 

due to exposure to wWBV. Development of more efficient 

supply handling systems, innovative approaches to supply 

handling problems and proper design of manual lifting tasks 

can greatly reduce the risk of back pain, as can attention to 

proper design of seating. 

Engineering controls that emphasize workstation and 

job design or redesign are first preferences for controlling 

or preventing WBV exposures and injury risk to vehicle 

drivers/operators. This type of control is preferred be­
cause it deals directly with the issues of WBV exposures 

and injury risk.Administrative controls such as switching 

out mining vehicle operators during breaks and lunch 

should only be considered as interim solutions until suitable engineering controls are available. Because they 

do not address WBV exposures and injury risk directly, 

administrative controls are less preferred measures. Some 

important guidelines to consider for a vehicle seat are 

to minimize vibration transmitted to the body with energy absorbing foam padding, provide a seat suspension 

(as appropriate and practical), provide adjustable back 

support (especially for the low back) and accommodate 

individual user differences with adjustability. n

Figure 10 

How WBV exposure at different vibration frequencies can affect different 

parts of the human body (Magid and Coermann, 1960). 

Footnotes 1 https://www.deere.com/en_AU/equipment/ag/tractors/5025_series/pf_cab.html 2 http://www.macdon.com/products/9000seriestractor/ 

9000seriesspecs.html 3 http://www.joy.com/jmm/products/pdf/Haulage_Brochure_Joy.pdf 4 Sun-mate Pudgee and extra-soft can be obtained 

from Dynamic Systems Inc., 235 Sunlight Drive, Leicester, NC 28748 (http://www.sunmatecushions.com/). 

Disclaimers 

 Mention of any company or product does not 

constitute endorsement by NIOSH. 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. 

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