Material: Recycled
Glass
Issue: All types of dust have come under increasing regulatory control in the
U.S. because of the potential or perceived health hazards they pose
toward workers. The Occupational
Safety and Health Administration (OSHA) sets standards for worker
exposure to airborne dust under Federal regulations 29CFR 1910.1000. The standards can substantially effect the cost of dust control
and material handling, as well as company liability for worker safety.
Container glass is made from over 70% silica. The term silica refers to the naturally occurring mineral silicon
dioxide (SiO2). Crystalline
forms of silica, also known as “free” silica, can contribute to certain
lung diseases under prolonged exposure conditions.
An understanding of the difference between glass dusts and
silica dusts in the crystalline form, and what the permissible exposure
limits are, is necessary to ensure worker safety and to avoid liability
in recycled glass processing.
Best Practice: Glass In considering glass dusts, it is important
to evaluate both the chemical composition of glass and its physical
state. Bottle glass is a silicate containing various
other ingredients which have been melted and upon cooling form an
amorphous, or noncrystalline structure.
The majority of the raw material silica occurs as quartz, a
crystalline form of SiO2.
Other crystalline forms of silica include tridymite and cristobalite. While SiO2 is a primary ingredient
in the manufacturing of bottle glass, when glass is formed, the crystalline
structure is changed to an amorphous structure and the SiO2 is
no longer considered crystalline.
The
permissible exposure limits (PEL) as defined in federal regulations
refer to a time-weighted average (TWA) based on an 8-hour workday
within a 40-hour work week. The
TWA is given in total airborne dust or respirable fraction (particles
less than 10 microns). OSHA classifies glass dust as a “nuisance dust”
with a TWA for total dust of 15 mg/m3, and a respirable
fraction of 5 mg/m3. Nuisance
dust exposures below the PEL are not recognized to be the cause of
any serious pathological conditions.
However, the level of any such dust should be kept as low as
is practical in the workplace (see Dust Control
Strategies for Glass Processing
Best Practice).
One
of the questions raised has been whether there is any de-vitrification,
or returning of glass to its crystalline state, in dust generated
by processing. In a study
performed by Dames & Moore Inc.(3) in 1993, samples
taken of dust generated during handling of glass cullet contained
less than 1% crystalline silica. A sample of the dust taken by a sampling pump
worn by a Dames & Moore employee showed <2.8% crystalline silica
(the accuracy limit of the abbreviated sampling time). When the 2.8% value is used to calculate the
TWA, total dust is below the limit.
Silica Pure crystalline silica has several different TWA values depending
on the type of crystal. The
OSHA TWA for 100% quartz is 0.3 mg/m3 total dust and 0.1
mg/m3 respirable fraction.
Because such pure crystalline forms are rarely found in industry,
calculations to determine the TWA are determined based on the percentage
of the most commonly found crystalline silicas in a particular type
of dust.
Silicosis is a type of pneumoconiosis resulting from
crystalline silica causing damage to the macrophages in the lungs. The macrophages release compounds that cause
fibrosis, or scar tissue. The
development of silicosis
does not appear to be related to only one factor. According to the National Safety Council, the disease depends on
several factors, including:
·
amount and
kind of dust inhaled
·
percentage
of free silica in the dust
·
form of silica
·
size of the
particles inhaled
·
duration
of the exposure
·
powers of
resistance or the individual concerned
·
presence
or absence of a complicating process (such as infection)
Implementation: It is recommended that processors
and users of recycled glass materials request Material Safety Data
Sheets (MSDS) for the particular types of glass being handled. The composition of post-consumer bottle glass
(see Identifying
Chemistry
of Container Glass Best
Practice) as collected through recycling programs is fairly
consistent, however periodic testing of both raw materials and dust
levels in the workplace is recommended.
Benefits:
Understanding
the hazards of dusts in the workplace is important in order to achieve
safe and efficient handling of recycled glass.
In certain uses for recycled glass, such as industrial mineral
applications, the nature of glass dusts appear to offer comparative
advantage over materials containing free silica, in terms of respiratory
health concerns. This may
translate to economic benefits realized by suppliers of recycled glass
competing with alternative fillers, abrasive grits, or other industrial
minerals containing crystalline silica.
Further, the benefits of understanding dust concerns and taking
protective measures can be quantified by the reduced exposure to liability
claims.
Application
Sites: Glass
processors, Material recovery facilities, Industrial users.
Contact: For more information about
this Best Practice, contact CWC mailto:info@cwc.org.
References:
(1)
Fundamentals
of Industrial Hygiene, Second Edition, National Safety Council, Chapter 7, pp 171-200.
(2)
Respiratory Health Aspects of Ground
Glass vs. Ground Silica, ReTAP Fact Sheet GL-94-1, Clean Washington Center,
1995.
(3)
Case
Studies for the Use of Post Consumer Glass as a Construction Aggregate,
Clean Washington Center Report
(4)
Code of Federal
Regulations (CFR), Occupational Safety and Health Standards, July 1, 1993 Edition.
(5)
Occupational
Health Guideline for Crystalline Silica, National Institute for Occupational Safety and Health
(NIOSH), September
1978.
Issue
Date / Update: November
1996
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