Mine Worker Fatigue and Circadian Rhythms

MINE SAFETY

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Mine Worker Fatigue and

Circadian Rhythms

How biological clocks respond to light and darkness

By Max Martell

The mining industry often uses shift work

schedules with the intention to have

a productive working mine around the

clock. However, one potential side effect

of operating on a 24/7 basis can be the

disruption of circadian rhythms, which re-

sults in worker fatigue — the mental state

between wake and sleep.

Fatigue from shift work has the poten-

tial to decrease productivity and increase

accidents in organizations where workers

are overly fatigued (Dawson et al., 2000).

In open pit mines fatigue-related ac-

cidents account for up to 65% of truck

driving accidents alone (Schmidt, 2015).

The detrimental effects of severe fa-

tigue include more than loss of produc-

tivity and accidents. Several potential

health effects are directly associated with

fatigue, including trouble sleeping, de-

creased alertness, slower reaction time,

and a weakened immune system. Workers

suffering from fatigue also show a general

decline in cognitive abilities, such as prob-

lem solving and working memory. More

serious health consequences of long-term

chronic fatigue may include diabetes, obe-

38 E&MJ • FEBRUARY 2018

sity, heart disease, and an increased risk of

cancer (Kecklund and Axelsson, 2016).

Although one cause of fatigue is lack

of adequate sleep, fatigue is not the

same as sleepiness. Additionally, fatigue

can result from the disruption of circa-

dian rhythms, also known as the body’s

“biological clock.” Circadian rhythms

are highly affected by the natural cycle

of daylight, and varying exposure to light

causes a disruption. Hence, shift workers

are inherently at risk of circadian disrup-

tion, with their working hours extending

into the night or early morning. This dis-

ruption can cause us to have problems

with getting enough sleep. Even one night

of poor sleep — deﬁ ned as either less

than seven consecutive hours or frequent

waking — can have negative effects on

our health (Watson et al., 2015).

Light and Circadian Rhythms

Short wavelengths of light, which are

mostly blue, are abundant in daylight.

The human eye’s responsiveness to these

short wavelengths is what causes the sen-

sitivity of circadian rhythms to daylight

(Figueiro et al., 2016). During the day,

the plentiful bright, blue light creates

alertness. At night, the lack of blue light

signals the brain that it is time to sleep.

However, for night shift workers, work-

ing at night and sleeping during the day

disrupts the normal day/night progression.

Furthermore, artiﬁ cial light sources such

as shop lights and computer screens dis-

rupt the natural cycle of light and dark after

sunset. These light sources are often high

in short wavelengths and attempt to mimic

daylight, since that spectrum of light im-

proves both visibility and alertness. This

leads to a disruption in circadian rhythms

by confusing the body into thinking it is

still daytime. As a consequence, workers

on the night shift can experience difﬁ culty

sleeping after their shift.

We also face a risk of circadian disrup-

tion during the day. When we do not get

enough blue light exposure throughout

the day, our body does not fully wake up.

Just as with the previous scenario, when

our biological clocks do not align with

the natural light cycle, the misalignment

can delay our normal period of sleep and

cause us to have trouble sleeping.

Underground miners are one group at

high risk for circadian disruption. Not only

do they often work shift schedules and

long hours, they may spend the majority

of the day underground, where artiﬁ cial

sources supply all of the light. Even with

bright white lights, like LEDs and ﬂ uores-

cents, it is very difﬁ cult to get light expo-

sure equivalent to that of daylight while

underground. On some underground min-

ing equipment, amber colored lights ﬁ lter

out much of the blue light. The problems

are made worse by the low reﬂ ectivity of

the environment, making the ambient

light darker as it reﬂ ects back very little

of the available light. Consequently, much

less light reaches the eye than normal.

Making the problem worse still is the ag-

ing population of the mining workforce.

As we age, our ability to see shorter wave-

lengths of light decreases, adding to the

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challenge of getting enough light expo-

sure while underground (Boyce, 2014).

Measuring Fatigue

People experience fatigue to varying de-

grees, and fatigue-causing factors affect

some more than others. A person’s age or

general health might affect their sensitiv-

ity to fatigue. However, there are ways to

measure fatigue, which can be a positive

ﬁ rst step in addressing it.

Subjective Methods–Subjective meth-

ods for measuring an individual’s fatigue

include surveys and self-questionnaires,

such as the Fatigue Severity Scale (FSS).

Although this scale does not exactly mea-

sure “severity,” it does help to evaluate

the impact that fatigue has on a person’s

daily life. In the same way, the Psycho-

motor Vigilance Test (PVT) determines the

impact of fatigue by measuring reaction

time and alertness, and the Karolinska

Sleepiness Scale (KSS) assesses subjec-

tively how sleepy a person feels. Thus,

these methods give us a way to under-

stand the problem on an individual level.

Objective Methods–More direct meth-

ods, such as measuring a person’s core

body temperature or taking blood samples

to measure hormone levels, can deter-

mine if there is a disruption of circadian

rhythms. However, these procedures are

highly invasive and cannot easily be done

in real time, making them impractical for

measuring fatigue in a working mine. Sa-

liva tests to measure the hormone mela-

tonin, a common indicator for circadian

rhythms, are somewhat more practical.

Other methods seek to identify fatigue as it

happens. These include facial recognition

and eye-tracking technology, which monitor

a worker’s apparent fatigue level. This ap-

proach can make workers uncomfortable,

however, as they might consider it an inva-

sion of privacy or disruptive to their work.

Dealing with Fatigue

A more active way of addressing worker

fatigue is to use a preventative method.

To control worker schedules and help

limit shift work and excessive overtime,

mine operators can implement a fatigue

management system. These types of sys-

tems may help to manage fatigue result-

ing from shift work by ﬁ rst detecting and

tracking it, and then making changes to

either avoid or manage fatigue over time.

Yet for underground miners, even with a

fatigue management system in place there

is still the problem with lack of sufﬁ cient

light. In this case, a lighting intervention

may help to prevent the disruption of circa-

dian rhythms. Other workers facing a sim-

ilar issue are those working in Antarctica,

who spend the sunless winter months in

dark, isolated areas where the only light is

from artiﬁ cial sources. Similarly, the crew

aboard U.S. Navy submarines may spend

months at sea without natural light while

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40 E&MJ • FEBRUARY 2018 www.e-mj.com

utilizing strict shift work schedules. Both

were able to successfully adopt a lighting

solution using highly blue-enriched light

sources to provide enough illumination

and short-wavelength light throughout the

day to reduce the misalignment of circadi-

an rhythms (Najjar et al., 2014; Young et

al., 2015), which also led to an increase

in alertness and quality of sleep.

Using these lights during the night

shift, however, would contribute to the

disruption of circadian rhythms. Yet work-

ers still need light to do their jobs. One

potential solution is to use light sources

with longer wavelengths of light falling in

the red spectrum. Research has shown

that red light can increase alertness and

performance without impacting circadian

rhythms (Figueiro et al., 2016).

Such a lighting solution would be chal-

lenging to implement in a mine environ-

ment, and the exact nature of an interven-

tion remains a subject for future research.

However, improving the lighting conditions

has the beneﬁ t of making hazards more vis-

ible to miners, and NIOSH researchers are

hopeful that it can also serve as an effective

fatigue intervention in underground mines.

Max J. Martell is a Mining Engineer work-

ing at the National Institute for Occu-

pational Safety and Health’s Pittsburgh

Mining Research Division. He can be

reached at: (412) 386-5855; Email;

[email protected].

Disclaimer

The ﬁ ndings and conclusions in this pa-

per are those of the authors and do not

necessarily represent the ofﬁ cial position

of the National Institute for Occupation-

al Safety and Health, Centers for Disease

Control and Prevention.

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