2420 Silica

Question 1

What is Silica?

Answer 1

SiO2
Silicon dioxide, a chemical compound.

One of the most commonly occurring minerals on earth.

Usually a major component of sand. Quartz is silica.

Question 2

What is silicon?

Answer 2

Si
Silicon

A chemical element.
Hard, brittle, crystalline solid.

8th most common element in the universe, and is rarely found in pure form in the earths crust.

Question 3

What is silicate?

Answer 3

Any anion of silicon and oxygen.

Often used to denote types of rock that a predominantly composed of silicon oxides.

Silicates constitute the majority of the earths crust. (eg, sand)

Question 4

What are the differences between crystalline and amorphous silica?

Answer 4

Crystalline silica is always more toxic than amorphous silica.

Question 5

What is crystalline silica?

Answer 5

Any compound of silicon dioxide that has a regular structure.

Question 6

What is amorphous silica?

Answer 6

Any compound of silicon dioxide that has an irregular structure.

Question 7

What workplaces and activities are at highest risk of crystalline silica dust overexposure?

Answer 7

Trade contractors (construction)

Building construction

Heavy and civil engineering construction

Metal ore mining

Cement and concrete product manufacturing

Question 8

What are silicones?

Answer 8

Silicones are polymers including any inert compound of repeating siloxane units.

Siloxane units are chains of alternating Si and O atoms.
Si-O-Si-O-Si

Question 9

Name a type of silicate mineral that is a famous hazardous material.

Answer 9

Asbestos.

Question 10

What is siloxane?

Answer 10

A siloxane is a compound including alternating chains of silicon and oxygen atoms.

Eg, Si-O-Si-O-Si

Question 11

Differentiate crystalline and amorphous solids.

Answer 11

Both are solids, and so there are atoms fixed in position with each other that vibrate.

Crystalline solids form repeating patterns, where the patterns of connected atoms all look the same (crystals, metals, salts).

Amorphous solids form irregular patterns, where the sections of atoms each look differently. (glass, wax)

Question 12

Compare the risks of silica exposure in processing silica sand versus making glass.

Answer 12

Both of these processes involve working with silica.
Silica sand is a crystalline silica, whereas glass is an amorphous silica.
The crystalline silica is more toxic than the amorphous form, as such the risks for the silica sand processing are higher than the making of glass.

Question 13

Discuss diatomaceous earth.

Answer 13

Diatomaceous earth is a siliceous sedimentary rock consisting of fossilized diatoms.
It is an amorphous silica in it’s natural state which is not very toxic.
It can be exposed to high heats to change it into a crystalline silica called “calcined diatomaceous earth”. This is more toxic and is often used as a ine filtration medium (example, in pool filters).

Question 14

Discuss “total”, “inhalable”, and “respirable” as occupational hygiene terms.

Answer 14

These terms all refer to the size of molecule where they can enter into the respiratory tract and cause illness.

Total, means the maximum size where the particle will cause illness (typically 100 microns and smaller)

Inhalable means the particles are small enough that they will pass the upper respiratory tract and enter the middle respiratory tract.

Respirable means the particles are small enough to pass to the lower respiratory tract and alveoli. (typically under 5-10 microns)

Question 15

What pictograms are applicable to silica?

Answer 15

Harmful to health.

No others.

Question 16

What factors affect the health effects of silica exposure?

Answer 16

The form of the silica (amorphous vs crystalline)

The silica particle size (are the particles small enough to get into lungs)

The dose, concentration x time (how much exposure)

Individual susceptibility

Question 17

What is silicosis?

Answer 17

A recognized occupational disease cause by exposure to silica dust.

Question 18

What are the health effects of concern related to silica?

Answer 18

Crystalline silica dust particles small enough to be respirated can cause:

• silicosis
• lung cancer
• COPD & pulmonary emphysema

Three forms of silicosis:
1, Acute silicosis (v.high concentrations, symptoms within a few weeks up to 5 years)
2, Accelerated silicosis (high concentrations, symptoms in 5-10 years post exposure
3, Chronic silicosis (low concentrations, symptoms after 10 years)

Question 19

Discuss pneumoconiosis

Answer 19

Pneumo (relating to the lungs)
Coniosis (dust)

“black lung”, “miner’s lung”, “dusty lung”, “brown lung”

Silicosis and asbestosis are both types of pneumoconiosis.

An interstitial lung disease where dust particles cause fibrosis in alveoli.

Question 20

What is the IARC?

Answer 20

The International Agency for Research on Cancer

Question 21

Is silica a carcinogen?

Answer 21

Crystalline silica is a known carcinogen.

Crystalline silica is an IARC group 1 carcinogen (known human carcinogen)

Question 22

List common materials that contain silica.

Answer 22

Rock and sand
Topsoil and fill
Concrete, cement, and mortar
Masonry, brick, and tile
Granite, sandstone, and slate
Asphalt (containing rock and stone)
Fibrous-cement board containing silica

Question 23

What are common work activities that expose workers to silica?

Answer 23

Abrasive blasting
Jackhammering
Cutting brick/tile
Grinding concrete
Road construction
Hauling gravel
Concrete demolition
Sweeping concrete dust

Question 24

What legislation governs the safety of silica in the workplace?

Answer 24

• No public safety legislation (as with toxic process gasses)
• General OHS legislation for hazardous material
• Specific legislation in BC OHS Regulation (Part 6) - includes prescriptive legislation.