Tackling the respirable hazards of crystalline silica in construction and related industries

For workers in professions such as
construction, abrasive blasting,
quarrying and stonemasonry,
some of the safety hazards and risks of
injury are obvious. Significant
occupational health hazards are also
posed to the respiratory system,
however. These hazards are less obvious
and health effects can occur over longer
periods of time if correct controls are not
in place.

Dust is generated when workers chip, cut,
drill or grind stone and rock and in many
cases this dust is created from a base
material which contains crystalline silica.

The dust may initially look innocuous,
but respirable crystalline silica can cause
disabling illnesses and may even in the
most serious cases result in cancer1.

Indeed, some 789 deaths from lung
cancer were attributed to silica in a 2010
Health and Safety Executive Research
Report, while there are more deaths due
to silica in the construction industry than
in any other sector2.

What is crystalline silica?
Crystalline silica is a fundamental
constituent of soil, sand, granite and
many other minerals. It is used as a raw
material in many processes and is found
in a wide range of building materials, such
as kerb stones and tiles. It is most
commonly found in quartz but is also in
other minerals such as cristobalite and
tridymite. When materials containing
crystalline silica are crushed, cut or
abraded, respirable crystalline silica may
be released.

If inhaled, respirable crystalline silica can
penetrate deep into the lungs, causing scar
tissue to form and hindering the lungs’
capacity to absorb oxygen – a condition
called silicosis.

What are the main health
problems?
The diseases associated with exposure to
respirable crystalline silica are
exceptionally unpleasant and, as well as
silicosis and lung cancer, include chronic
obstructive pulmonary disease (COPD).

Silicosis can occur in two main forms
depending upon the duration of the
exposure and the concentration of silica.

The most common form is chronic
silicosis, caused by prolonged exposure to
medium to low concentrations of silica,
with symptoms ranging from fatigue and
shortness of breath to chest pain. Chronic
silicosis can be extremely disabling and
may lead to premature death3.

Acute silicosis is caused by excessive
contact with exceptionally high
concentrations of silica, and symptoms
can present after only a few months.

These include severe, disabling shortness
of breath, weakness and weight loss,
which can be fatal 4.

Lung cancer is the most common form
of cancer-related death and exposure to
silica is the second largest cause of
occupational lung cancer, second only to
asbestos2. Its symptoms include shortness
of breath, coughing blood and weight
loss. While it is widely associated with
smoking, there is some evidence that
suggests that lung cancer is even more
common in smokers who are exposed to
silica.

COPD is the name given to a number
of lung conditions, including chronic
bronchitis and emphysema, which
prevent the sufferer from breathing
properly. As the condition progresses, this
worsens and can become extremely
debilitating. The symptoms of COPD are
similar to those of asthma but while
asthma can be controlled, once COPD
develops the damage to the lungs cannot
be reversed5.

Who is affected and where?
Exposure to silica occurs in multiple
construction operations – these can range
from cutting paving stones and
kerbstones with rotary cutters, through to
abrasive blasting with sand to remove
paint from concrete structures and other
surfaces. Other operations which may
result in contact include using pneumatic
drills, rock drilling, concrete mixing,
concrete drilling, demolition and
tunnelling operations.

Silica exposure is also an issue in
cement and brick manufacturing, china
and ceramic manufacturing, and the steel
and foundry industries. Meanwhile,
exposure can occur in the maintenance,
repair and replacement of refractory brick
furnace linings.

What does the law say?
Exposure to respirable crystalline silica
(RCS) is governed by the Control of
Substances Hazardous to Health
Regulations (COSHH).

The Workplace Exposure Limit (WEL)
for respirable crystalline silica is 0.1mg/m?
averaged over an eight-hour period and
legally, exposure levels must not exceed
this limit.

Over a period of 15 years, even at this
daily exposure limit, workers still have a
one in 40 chance of developing silicosis.

Reducing the exposure level to
approximately half this amount cuts the
risk by five times. However, exposure at
three times the limit would increase the
risk of developing silicosis by eight times6.

It is because of these risks that the
Health & Safety Executive (HSE) states
that, for the construction industry,
exposure to silica must be controlled to as
far below the WEL as is reasonably
practicable.

Managing exposure
There are three steps to which employers
should adhere in the hierarchy of control
in order to minimise exposure to
hazardous substances. The first is the
elimination or substitution of working
methods and materials, followed by
engineering controls. Both of these must
be thoroughly explored before the final
step – the use of personal protective
equipment (PPE) – is considered.

The first step requires employers to
establish whether or not the product
containing the hazardous substance, or
the process generating it, can be
eliminated or substituted. For silica, this
might involve using a material containing
less, or ideally zero, silica, or eliminating
the need for cutting kerbstones, for
example, by using pre-cut products.

The next step is to use engineering
controls. For indoor processes, these can
include local exhaust ventilation. For
other processes, such as cutting kerb
stones, the HSE requires the use of water
suppression. Finally, PPE may be used if
required to reduce exposure to acceptable
levels.

In its latest guidance for the control of
silica dust in the construction industry,
the HSE goes even further, stating that
respiratory protective equipment (RPE)
must be worn in addition to other control
measures.

Specifying and selecting RPE
Specifiers can select from disposable, halfmask,
full-face or powered respirators
depending on the level of exposure,
identified through risk assessment, nature
of the task and personal preference.

Disposable respirators are available in
three levels of protection – FFP1, FFP2
and FFP3. The HSE guidance for silica
dust requires the use of respirators with
an assigned protection factor (APF) of at
least 20 – this means that exposure is
reduced by at least a factor of 20 when the
product is face fit tested and worn
properly by a trained user. If a disposable
respirator is preferred an FFP3 respirator
should be selected.

Many disposable respirators are ‘single
shift’ products and so should not be used
for more than day, while others have
cleanable face seals making them suitable
for limited re-use if kept in a good
condition. Products which are suitable for
limited re-use will be marked “R”, while
those which are for single use only will be
marked “NR” as dictated by the European
Standard EN149:2001+A1:2009.

Disposable respirators come in a
variety of shapes and sizes, from cupshapes
to ‘fold flat’ to meet individual
preferences. While the majority of
products have fixed length straps, some
come with adjustable straps to help
accommodate different face shapes.

Reusable half-mask and full face
respirators consist of a facepiece and
replaceable filters which can be reused for
days or even weeks before needing to be
changed. When fitted with a P3
particulate filter, a half-mask offers an
APF of 20, while a full face mask offers an
APF of 40. The filter needs to be changed
when the wearer experiences increased
breathing resistance.

Reusable respirators to must be
maintained if they are to offer effective
protection. Maintenance includes pre-use
and post-use checks, care and
maintenance, and consumable
replacement when necessary. Appropriate
storage when not in use is also important.

Disposable and reusable half-masks and
full face respirators are classed as ‘tight
fitting’ respirators and before first use, it
is a legal requirement to conduct a fit test.

There are two types of fit test – qualitative
(suitable for disposable respirators or
half-masks) and quantitative (suitable for
full face respirators including full
facepieces fitted to a negative pressure or
powered or positive pressure device). Fit
testing gives an assessment of facial fit to
an individual RPE wearer. Quantitative
testing gives a fit factor (an actual
number), while qualitative provides a pass
or fail result.

It should also be remembered that
wearers of tight fitting respirators must be
clean shaven, not only on the day of the
fit test but every time they use the
product. Even a small amount of stubble
can affect the quality of the seal to the
face.

Employees should be instructed to fit
the respirator well, to perform all
necessary fit checks before entering the
affected area and not to remove it in the
hazardous environment. Removing the
respirator even for a few minutes can
dramatically affect the level of protection
offered.

The role of powered respirators
Powered air respirators have a higher
unit cost but are frequently considered a
more comfortable option for wearers
working in hot or humid conditions, or
whose work is physical or lasts a long
time. They offer high levels of respiratory
protection and are also available with
integrated head, eye and face protection
which can overcome the problems of PPE
compatibility. Powered air respirators are
loose-fitting, meaning the face seal is less
critical than with tight-fitting respirators
and fit testing is not required.

As with reusable respirators, powered
air respirators must be well-maintained
with regular checks. Monthly records
must be kept and able to be produced on
demand at an HSE inspection.

As well as providing RPE and training
in its use, employers must ensure that
correct work methods are followed and
that an appropriate health surveillance
programme is established.

Training employees
The HSE requires that wearers of PPE are
trained in its use and it is recommended
that workers who may be exposed to silica
are trained on its potential health effects
and how exposure might be controlled.

Training may include:
How to conduct the task in a way
which minimises exposure
The use and maintenance of dust
suppression and extraction equipment
Care and maintenance of PPE,
including storage
How and when to wear PPE, including
correct fitting and use.

Keeping surfaces clean as this helps
prevent dust becoming airborne again.

3M is featuring an articulated
presentation on Silica on its segment page
www.3M.co.uk/construction. The
company also offers a number of services,
including quantitative or qualitative fit
testing. For product and support
information call 0870 80 800 60 in the UK
or 1 800 320 500 in Ireland. For more
information on 8300 series disposable
respirators and free product samples, visit
www.3M.co.uk/comfortcounts.

For more information please visit
www.3M.co.uk/ohes.

References
1. http://www.hse.gov.uk/quarries/silica.htm. Viewed18/10/2010
2. HSE Research Report 800, The Burden of Occupational Cancer in
Great Britain (2010).

3. http://www.hse.gov.uk/construct