1. Gaynor Guthrie Medical Inspector
Silica Dust:
You Are More At Risk Than You May Think
Who are you:
Priority inspection topic for the forthcoming year – Silica
Gaynor Guthrie
Medical Inspector

2. “It’s only dust you know!”
This is what hear all the time – 95% of people talk to.

3. What is the Problem?
Silica is found in sand but is not a hazard as it is not fine enough to be inhaled – see next slide
Silicon dioxide (SiO2)

4. Why is it a Problem? Particles need to be “respirable” to cause harm
Issue is Respirable Crystalline Silica or RCS
RCS particles can penetrate to deep lung
Cutting, drilling, grinding or polishing silica containing products such as kerbing, paving, blocks and concrete produces airborne dust. This contains a range of crystalline silica particle sizes, some of which can be inhaled.
The larger inhaled particles enter the main passageways of the lungs (bronchi) but are prevented from passing through the very small passageways due to their size. They tend to get coughed out.
3) Respirable particles are the tiny particles which are small enough to reach deep into the lung to the alveoli which are the little sacs at the end of the tiniest passage. Here oxygen is taken up by the blood and carbon dioxide is released from the blood into the air.
4) Freshly cleaved particles of RCS are more dangerous than ‘aged’ silica eg those generated during many common workplace tasks such as drilling, cutting, grinding or polishing.

5. Why is it a Problem? A micron is one millionth of a meter.
Human hair varies between 40 to 100 m thick.
Respirable dust = 10 m or less
The particles of sand are too big to be respired.
RCS is 10um or less so can be reach deep into the lung.
RCS is invisible under normal conditions.

6. Silicosis ?10 to 20% construction workers exposed
Silicosis usually follows at least 10 years of exposure to RCS
It causes stiffening and scarring of the lungs. Nodules visible on X-Ray
Symptoms are coughing and breathlessness
Progressive, even after exposure stops
1) It is not known for sure how many construction workers are exposed. One HSE study put the number of workers regularly exposed to RSC at around 10% of the total workforce.
Another HSE funded study has taken data from the international CAREX database and estimated that between 1990 – 93 around 450,000 workers were exposed. Whatever the true figure it is likely to be significant.
2) Risk depends on how much crystalline silica the worker is exposed to and how long the exposure is.
The risk of developing disease for construction workers depends on the accumulated dust burden (i.e. dose) of individuals over many years. Each exposure episode builds on previous exposures and so the risk of developing ill health increases. Consequently there is a need to control every single occupational exposure.
3) By the time the worker develops symptoms, the disease is usually in an advanced stage.
The only way to detect silicosis in an early stage is with a chest X-Ray. (Nb Ionising radiation has its own risk of increasing risk of lung cancer)
4) Slowly progressive. Even if worker is removed from exposure, the disease can progress.
5) An acute form of silicosis following very high exposure is less common but can be rapidly fatal (a few months)
What could this mean in practice for a construction worker exposed to RCS above the exposure limit over a long period, for example from the age of 20 to 40, who goes on to develop associated lung disease? In the early stage of lung disease an individual may notice some occasional breathing difficulties, occasional breathlessness when running and possibly bouts of persistent coughing. Later on as the disease progresses an individual may need an inhaler and find that they cannot sleep properly through the night. They cannot play sport and walking long distances may also be difficult. By the time the individual reaches 60 they could be housebound and in need of regular portable oxygen from a cylinder via a mask. Their doctor may be advising them that they could soon need a wheel chair. In layman’s terms this means “a young healthy lad starting work at 20 who cannot breathe at 60”.

7. Silicosis Irreversible Increased risk of Tuberculosis (TB)
After 15 years of exposure to RCS at the WEL of 0.1mg/m3, the risk of developing silicosis is 1 in 40
Silicosis is under-reported.
1) Irreversible even if remove worker from exposure
2) Risk of developing tuberculosis proportional to severity of silicosis on X-Ray.
3) Risk of developing silicosis after 15 years at the old MEL of 0.3mg/m3 is 1 in 5.
4) Often reports refer to small number of deaths drawn from large worker populations, so you don’t hear about it much. But, statistics on lung cancer much better..

8. Normal chest X-Ray
Normal chest X-Ray
Taken from Wikipedia

9. Tuberculosis
Reproduced from wikipedia. The tuberculosis is the cluster of opacities where the arrow is pointing

10. Lung cancer There is an association between silicosis and lung cancer
Over 500 silica related lung cancer deaths in construction in 2004 – Over 10 a week
Silica is the second most important cause of occupational lung cancer after asbestos
1) It might be that it is necessary to have silicosis before you get silica induced lung cancer.
The association between silicosis and lung cancer is more pronounced in smokers.
Commonest cause of lung cancer is smoking (responsible for 90% cases).
2) However, HSE estimates that approximately 2,000 deaths per year in construction are due to occupational lung cancers, most of which asbestos-related.

11. Lung cancer
Reproduced from Wikepedia. The lung cancer is the opaque area within the box.

12. Lung cancer Second commonest cancer in men after prostate
Symptoms: cough (phlegm and blood), pain on breathing or coughing, shortness of breath, weight loss
Only 7% men survive 5 years after diagnosis

13. Chronic Obstructive Pulmonary Disease (COPD)
Persistent obstruction of airflow into lungs
Irreversible (unlike asthma)
Progressive
Main cause is smoking
Silica exposure associated with COPD
Construction workers 2 to 3 times risk
Symptoms: breathlessness, cough with phlegm
COPD is a disorder in which there is persistent obstruction of airflow into the lungs. COPD encompasses chronic bronchitis and emphysema.
2) COPD mostly irreversible. A small portion of the narrowing in airways can be reversed in some people with inhalers etc but most can’t. Overall, once you have developed the condition you are stuck with it. Asthma involves reversible obstruction of airflow into the lungs.
3) Condition produces symptoms in middle or old age: SOB, cough with phlegm
4) Both diseases progressive over time unless the cause is removed unlike silicosis.
5) HSE estimates 4,000 deaths/year across industry due to COPD due to occupational causes.
Construction workers show two to 3-fold increase in COPD illness and mortality compared to age and smoking matched reference groups. In other words, working in construction is a risk factor for COPD regardless of smoking habits.
Causative agents include wood dust and silica.
6) As well as background breathlessness, cough with phlegm, people with COPD are more likely to get chest infections.

14. Health Surveillance G404 Health surveillance for RCS
Use a health professional
Risk based
Symptom enquiry (COPD, TB)
Lung function test
Chest X-Ray
1) G404 covers HS for all respiratory conditions caused by silica. Principally, COPD, silicosis, TB. (No suitable tests for lung cancer)
2) The health professional will help with RA to determine if HS necessary, particularly if Chest X-Ray needed. (Ionising Radiation adds small risk of lung cancer) Will interpret results of tests and monitor trends in groups of workers and encourage smoking cessation. Perform baseline tests: questionnaire, lung function, Chest X-Ray if needed.
3) When the MEL was 0.3mg/m3 HSE guidance stated that chest X-Ray should be done at particular frequencies, every 5years for 20 years then every 3 years.
Since the WEL came down to 0.1mg/m3, the guidance has been the frequency of health surveillance including X Ray should be risk based.
3) Baseline assessment always appropriate where risk of silicosis.

15. How Much is a Problem? COSHH sets WEL for dust: General Dust
10 mg.m-3 (inhalable)
4 mg.m-3 (respirable)
Respirable Silica
0.1 mg.m-3 (8-hour TWA)
If you inhaled the small amount of RCS illustrated in a day you would exceed the WEL
Any questions?