Silicosis and Silica
Health Hazards of Crystalline Silica
Temporary: Coughing, and mild temporary irritation following a short exposure.
Skin Contacts: Not irritating. However if through an injury: foreign body reactions (graulomas) have occurred. Effects observable from weeks up to more than 50 years.
Eyes: Irritating. Possible corneal opacities. But documentation is not yet clear or conclusive.
Ingestion: No known effects.
Inhalation and Silicosis:
This is the main health issue, and of the greatest concern. It has been estimated that around 2 million workers in the USA are exposed to Silica and that 10% are at risk for developing Silicosis. On a more worldwide scale, this number goes up dramatically, especially more so in developing countries where protection isn't practiced/enforced.
Consider just some numbers. Australia - >1000 cases predicted annually, Japan >1000, Germany, around 3000, France around 300, and UK 1164 cases. Compare to the developing countries: Brazil 6.6 million exposed to silica, Colombia > 8 million exposures, India ~ 7 million, and China 60,000 cases of Silicosis, ~ 10 million exposed.
What happens with Crystalline Silica, is that the smaller particles become lodged in the small air passages (bronchioli) and air sacs (alveoli). Then the human body sends its natural defense mechanisms, macrophages, to attack the silica particles. The Silica kills the macrophages. The body sends more, and the cycle keeps repeating. The results are the hardening, scarring and stiffening of the lungs. In the early stages of Silicosis there may not be any signs, also note this disease continues even after the worker is no longer exposed to Silica dust.
Silicosis is nonreversible, each year about 250 American workers die with it. There is no known cure and it is preventable. In the 1930's it reach epidemic proportions, and jumped from the obscure, at that time it is estimated that 700 men died from one incident (Hawk's Nest Tunnel). Deaths fell from 1157 in the 1968 to 148 in 2002. The decrease is attributed to federal limits on the amount of exposure to Crystalline Silica. It can be traced back to as early as 1556, here it was described as pulmonary disease afflicting stonecutters and miners.
Silica related diseases are associated only with Crystalline Silica and not amorphous. Amorphous lacks structure, were as crystalline has structure.
There is no cure for Silicosis.
- shortness of breath during times of exertion or exercise. (when of the first signs)
- Mucous production high
- Severe cough
- Occasional bluish skin at ear lobes or lips
- Loss of appetite
- Chest Pain
Other complications can result from Silicosis and these are:tuberculosis, scleroderma, rheumatoid arthritis, and systemic lupes erythmatosis. As well as Lung Cancer. The International Agency for Research on Cancer (IARC) has concluded that crystalline silica in the form of quartz or cristobalite from occupational sources should be classified as carcinogenic to humans (Group 1).
Life expectancy is reduced, and though a person may not die directly of Silicosis, it is more from the complications that occur: more restricted blood flow to the lungs, and a harder working heart.
Silicosis can be detected through X-rays even when no symptoms are apparent. It shows up as nodular in appearance in the lungs. In more severe cases the nodules will be joined together.
Low concentrations over long periods of time or high exposure levels over a short period of time can lead to Silicosis.
Three types of Silicosis:
- The lungs become very inflamed and can fill with fluid, causing severe shortness of breath and low blood oxygen levels
- Develops with weeks and up to 5 years. Exposure to large levels of Silica
- Develops between 5 and 10 years – moderate exposure levels.
- Swelling in Lungs
- 10 or more years of mild or low exposure levels Undetected for years and most common
Safety for Silica:
Recommended Exposure limits (REL) for Crystalline Silica is 0.05 mg/m^3 (50g/m^3) as a TWA for up to 10 hours/day during a 40-hour workweek [NIOSH 1974].
It should be noted that the lungs cannot expel Crystalline Silica at or below 10 microns in size, in particular particles freshly cleaved and around 1mircron are the most hazardous.. Your mucous membranes can handle particles greater than 10 microns and is removed from the respiratory tract. As expectorant (flam) or swallowed – this all takes place in your larger airway passages.
NIOSH recommends: the use of half-facepiece particulate respirators with N95 or better filters for airborne exposures to crystalline silica at concentrations less than or equal to 0.5 mgm3. The Occupational Safety and Health Administration (OSHA) also specifies the use of at least a 95-rated filter efficiency [29 Code of Federal Regulations (CFR) 1910.134]. The recommendation for a 95-rated filter efficiency reflects the improved filter efficiency of N95 filters over the earlier dust and mist (DM) filters.
The rationale for a lower NIOSH filter, is easier breathing through the N95 vs N100, thus making it more comfortable for the worker.
NIOSH Filters (NIOSH federal respiratory regulations 42 CFR Part 84 )
- N95 - filters 95% of particles of .3 microns
- N99 - filters 99% of particles of .3 microns.
- N100 - filters 99.97% of particles of .3 microns.
The Construction Safety Association of Ontario stats this:The type of respirator used will depend on the level of silica in the air. As a minimum, a half-facepiece N100 respirator should be used. As the amount of silica dust increases, the respirator must offer more protection. For example, dry cutting masonry stone over a prolonged period may require a full-facepiece respirator instead of a half-facepiece respirator. A half-facepiece respirator only fits over nose and mouth whereas a full-facepiece respirator fits over eyes, nose, and mouth and offers better protection.
To work properly for these percentages requires that the facepieces be properly fit tested and maintained (not just dropped in a bag and forgotten till the next time). The wearer be clean shaven (even stubble will allow leakage).
Respirators provide protection two basic ways:
- Removal of contaminants from the air – Particulate first, airborne particles and “gas masks” to filter out chemicals and gases.
- Supply clean respirable air from another source.
They are to used as a “last line of defense”. In other words when control systems are not feasible.
Some of NIOSH recommendations for reducing exposure to respirable crystalline silica.
- Plan ahead to eliminate or reduce or control the dust at the source
- Use a substitute if you can
- Engineering controls: Ventilation methods, wet sawing/drilling, dust collection systems.
- Maintenance of dust control systems
- Good personal hygiene – eating areas separate from work, washing of hands and face.
- Wearing disposable or protective clothing as the work site – avoid taking containments home or in car.
- Don't blow down or dust off your containmented clothing.
- Use adequate respiratory protection when source controls cannot keep silica exposures below the NIOSH REL (for respirable crystalline silica is 0.05 mg/m^3 (50g/m^3) as a TWA for up to 10 hours/day during a 40-hour workweek [NIOSH 1974]. )
- Post area for protection of others.
OSHA Exposure Limits for Silica Dust Exposure
The current OSHA permissible exposure limit (PEL) for respirable crystalline silica (quartz) is 100 µg/m3 as an 8-hour time-weighted average (TWA) [29 CFR** 1910.1000]. The NIOSH recommended exposure limit (REL) for respirable crystalline silica is 50 µg/m3 as a TWA (time weighted average) for up to 10 hours/day during a 40-hour workweek [NIOSH 1974b]. This REL is intended to prevent silicosis. However, evidence indicates that crystalline silica is a potential occupational carcinogen [NIOSH 1988a; IARC 1987; DHHS 1991], and NIOSH is reviewing the data on carcinogenicity.
Preventative Measures and drawbacks:
Methods their advantages and disadvantages
see additional notes
- Need for water on job site
- Best reductions on open flow non-recirculated water (continuous fresh supply)
- Particulate control dependent on water flow
- Heavy equipment, two man job
- Without water filters, recirculated water will allow higher particulate concentrations
- Architect requirements: possible water staining
- Architect/Structural: Dry bricks or blocks for maximum strength. (precutting well in advance)
- No water cutting on roofs.
- Weather dependent if done outside. Freezing limitations.
- If done inside, enclosed areas, particulate levels can easily exceed safe levels from 2-4 times.
- Electrical problems of water and electricity.
- Significant reductions in Silica: depending on flow, recirculation, water filters, and confined or open areas.
- Respirators need to fit tested to the person
- Dust clean up depending on where set up was.
- Outside setup: Weather dependent.
- Worker needs to be clean shaven, no beards or mustaches. Even stubble can affect the seal. Thus reducing the efficiency of the filter.
- In Hot weather respirators can more uncomfortable.
- Higher rated respirators can be more difficult to breath through.
- Simple face masks are only good for infrequent low exposures
- Last line of defense
- Maintenance of Respirators. Keeping them clean, stored properly (not bottom of tool box).
- Replacement filers needed
- Sight still needs to be cleaned of dust or not walked through.
- Disposable or protective clothing, no dusting off or blow downs.
- Allows for easy setup of Dry cutting.
- Protection can be from 95 – 99.97% depending on respirator used, and it's rating (N95, N99, N100 so on)
- Easy set up
- Ventilation must be properly set up.
- Usage of fans (fresh air supply, exhaust) extra equipment.
- Open air, with good breeze behind worker. Not always possible.
- Good air flow, flowing from worker to saw. Directing plume away from him.
Dust collector systems
- Depending on the system: Big, awkward, and more expensive.
- Smaller, shop vac systems, extra hoses, and extension cords., extra equipment.
- Filters still need to be inspected and replaced, but easier.
- Collects particulates at source
- Takes the dust away from the Worker and Co Workers.
- No Dust clean up afterwards
- Easier filter changing or monitoring.
Dry Cutting systems with Portable Dust collector mounted
Filters still need to be changed or cleaned.
Slightly heavier than regular Dry cutting saw.
- Collects particulates at source
- Takes dust away from cutter
- No Dust clean up afterwards
- Easy filter changing and monitoring. Usage of HEPA filters 99.97% .3 microns (equivalent to N100 filters)
- Easy setup, can be used on scaffolding and roofs.
- Single extension cord, no extra equipment.
Wet Cutting/Drilling, this method greatly reduces the particulate level.
Here the effectiveness will depend upon the water delivery and whether it is fresh or recirculated. From Evaluation of Misting Controls to Reduce Respirable Silica Exposure for Brick Cutting, a study was done. It was found that amount of water being used to control the dust, greatly affected the amount of particulate level. Misting nozzles produced from 63 to 79 percent reduction in comparison to no dust control. However the most effective was just free flowing water: achieving a 93 percent reduction. This was done in a enclosed area, with non-recirculated water (fresh water all the time).
From this we can project that using recirculated water will increase the particulate level. So the percentages can be expected to drop but still far preferable to no controls. It has been found that with no controls in place and out in the open the exposure levels can rise to 10 times that . With wet cutting at moderate rates of water flow, recirculated, the exposure level can be expected to exceed the safe levels by 2- 4 times the permissible levels. The safest even for wet cutting is out in the open. For more information on wet cutting see the University of Washington reports.
As previously noted this is your “last line of defense”. You need the appropriate protection for the exposure you in. Additionally fitting and facial hair affects the performance of respirators.
Ventilation: Open air cutting, with air flow directing the particulate plume away from the worker and nearby workers. Not always feasible, due to weather conditions, or building design.