Transcript Respirable Crystalline Silica

RESPIRABLE CRYSTALLINE
SILICA
New Considerations
for Sampling and
Analysis
SILICA IS A
TOPIC
IN THE U.S.
SKC INC.
is pleased to share the
latest updates.
BUT FIRST CONSIDER:
SILICA THE COMPUND
Look at chemical formula for silica (SiO2), and consider
this:
 Oxygen is the most abundant element in the Earth’s
crust and silicon is the second most abundant.
 Quartz, the most common form of crystalline silica, is
the second most common mineral on the earth’s
surface.
 Amorphous silica such as diatomaceous earth is not
particularly toxic to humans unless heated to high
temperatures.
CRYSTALLINE SILICA:
WHERE ITS FOUND
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Crystalline silica is
naturally occurring in
sand, gravel, and
mineral ores.
Quartz, the most
common form, is found
in almost every type of
rock.
Nearly all mining and
quarrying activities
involve exposures to
crystalline silica.
CRYSTALLINE SILICA:
WHERE ITS USED

Due to its chemical and
physical properties,
crystalline silica is a
prized mineral with a
number of industrial
applications.

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Major ingredient in
building materials such
as concrete, bricks, and
stone
Used as a molding
material for metal
casting in foundries.
Filler in plastics, rubber,
and paint.
Raw material for glass
manufacture along with
porcelain and fine
china.
APPLICATION IN THE HEADLINES:
FRACKING

Silica sand is used to
hold open the fissures
created by hydraulic
fracturing (fracking) so
natural gas or oil can
flow out of the shale
and into the well.
CRYSTALLINE SILICA:
WORKPLACE EXPOSURES
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U.S. OSHA reports that 2.2 million workers
are exposed to respirable crystalline silica.
The majority (1.85 million) are in the
construction industry.
Exposures occur when workers cut, grind,
crush, or drill silica-containing materials.
CRYSTALLINE SILICA:
WORKPLACE EXPOSURES
High Risk Jobs:
 Abrasive blasting
 Foundry work
 Stonecutting
 Rock Drilling
 Mining
 Tunneling
 Hydraulic Fracturing
NEW PROPOSED RULE
FROM U.S. OSHA
In September 2013, U.S. OSHA published a
Notice of Proposed Rulemaking (NPRM) for
Occupational Exposure to Respirable Crystalline
Silica.
 This is the first update since the original
Permissible Exposure Limit (PEL) was adopted
in 1971.
 See this 757-page document at
https://www.osha.gov/silica/nprm.pdf

SUMMARY OF ISSUES IN THE NPRM
AFFECTING SAMPLING & ANALYSIS
1.
2.
3.
4.
New Permissible Exposure Limit
New Specifications for Respirable Dust
Samplers
Guidance on Sample Times required to
exceed limit of quantification at the
proposed levels
Guidance on Analytical Methods that are
sensitive enough to measure silica at
proposed levels
PERMISSIBLE EXPOSURE LIMIT:
EXISTING
GENERAL INDUSTRY
A formula based on the % silica
in the air sample. Example:
_____10____
% Quartz + 2
PEL is equivalent to 100 ug/m3
when the material is pure
quartz . PEL approaches 5
mg/m3, (the PEL for Particulates
Not Otherwise Classified) with a
low percentage of quartz in the
sample.
CONSTRUCTION AND
SHIPYARDS
A formula based on obsolete
method of collecting dust into
impingers with analysis by
particle counting.
PEL is approximately
equivalent to 250 ug/m3.
PERMISSIBLE EXPOSURE LIMIT:
PROPOSED
50 ug/m3 as an 8-hr TWA for all forms of
silica including quartz, cristobalite, and
trydymite for all industry sectors covered by
the rule.
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25 ug/m3 action level (same as current TLV)
SPECIFICATIONS FOR
SAMPLERS: EXISTING
Existing specs for respirable dust samplers were
promulgated in 1971 and are listed in 29 CFR
1910.1000; Table Z-3 for mineral dusts.

A respirable dust sampler with a 50% (median)
cut-point of 3.5 um is specified.

The Dorr-Oliver (nylon) cyclone is the only
sampler used by federal OSHA inspectors to meet
the existing specifications.

U.S. OSHA IS TRYING TO UPDATE
TO CURRENT AEROSOL SCIENCE
Page 539: OSHA acknowledges that the existing
collection efficiency specifications for respirable dust
samplers (50% cut-point of 3.5 um) are obsolete.

Page 542: OSHA states that crystalline silica
measurement should be determined by a sampling
device designed to meet the characteristics for particlesize-selective samplers specified in ISO 7708:1995 Air
Quality-Particle Size Fraction Definitions for
Health-Related Sampling.

ISO 7708:1995

This is the standard that ACGIH, NIOSH,
CEN, and most countries around the world
have already adopted.

The collection efficiency curve for respirable
dust samplers in this standard includes a
50% (median) cut-point of 4 um which is
more conservative than the existing OSHA
specification of 3.5 um.
RESPIRABLE DUST SAMPLERS:
TO MEET ISO 7708
SPECIFICATIONS
OPTION #1:
TRADITIONAL CYCLONES
CYCLONE SAMPLERS:
TO MEET SPECS IN ISO 7708
NYLON DORROLIVER CYCLONE:
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Listed in OSHA SILICA
NPRM on page 267
Listed in NIOSH
respirable dust methods
Designated flow rate is
1.7 L/min (same as that
used for previous
criteria?)
DORR-OLIVER CYCLONE
ADVANTAGES AND DISADVANTAGES
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Advantage: Long history of use in the U.S. by
compliance officers.
Disadvantage: Nylon construction creates
static electricity concerns.
Disadvantage: Orientation bias. (AIHA Journal
56, November 1995).

Disadvantage: Dust sticks to cassette top
with closed-face operation. (ASTM, STP 1565,
2013)
CYCLONE SAMPLERS:
TO MEET SPECS IN ISO 7708
SKC ALUMINUM
CYCLONE:
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Listed in NIOSH
respirable dust methods
Published performance
(J. Aerosol Science, 29,
1998).
Designated flow rate is
2.5 L/min
SKC 225-01-02
ALUMINUM CYCLONE
ADVANTAGES AND DISADVANTAGES
ADVANTAGES

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Metal construction
eliminates static
electricity concerns.
Open-face sample
collection enhances
collection.
Calibration adapter
offers user
convenience.
DISADVANTAGE

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Aluminum can not be
used in underground
mines due to spark
hazard.
Users frequently make
the mistake of removing
the red cap (grit pot) on
the cyclone during
sampling.
CYCLONE SAMPLERS:
TO MEET SPECS IN ISO 7708
SKC G(S)-3:
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

.
Listed in OSHA SILICA
NPRM on page 267
Published performance
(J. Aerosol Science, 28,
1997).
Designated flow rate is
2.75 L/min
SKC 225-100
GS-3 CYCLONE
ADVANTAGES AND DISADVANTAGES
ADVANTAGES

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Designed to overcome
orientation bias of DorrOliver
Conductive plastic
construction eliminates
static electricity concerns.
Not a spark hazard for
underground mines.
Open-face sample
collection enhances
collection.
DISADVANTAGES

No calibration adapter
like with aluminum
cyclone. Requires
calibration jar or the
easier jarless
calibration methods.
CYCLONE SAMPLERS:
TO MEET SPECS IN ISO 7708
BGI GK 2.69
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Listed in OSHA SILICA
NPRM on page 267
Designated flow rate is
4.2 L/min
Now available from
SKC as 225-269-37 or
-25 for 25-mm version.
BGI GK 2.69 CYCLONE
ADVANTAGES AND DISADVANTAGES
ADVANTAGES

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Metal construction
eliminates static
electricity concerns.
Higher flow of 4.2 L/min
allows users to sample
only 4 hours to collect
enough sample for
quantitative analysis of
even cristobalite at the
action level.
DISADVANTAGES


May not be suitable for
use in underground
mines.
No calibration adapter
like with aluminum
cyclone.
IMPORTANT NOTE ON FLOWRATE
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All cyclones are not
created equal!
Each cyclone has
different operating
specifications and
performance criteria.
Be sure you know the
flow rate specified to
achieve the desired cutpoint before using any
cyclone.
TECH TIP:
CASSETTE MATERIAL
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In a March 2013 JOEH article by NIOSH, cassette
wall losses were noted when using cyclones with
typical cassettes made of styrene*.
NIOSH recommends the use of 37-mm black
conductive cassettes made of polypropylene.
*Ashley & Harper (2013) Analytical Performance Issues, Journal of
Occupational and Environmental Hygiene, 10:3.
RESPIRABLE DUST SAMPLERS:
TO MEET ISO 7708 SPECIFICATIONS
NEW
OPTIONS
NEW SAMPLERS:
TO MEET SPECS IN ISO 7708
Page 539 of OSHA SILICA NPRM states:
Adoption of this (ISO) definition by
OSHA would allow for workplace sampling to
be conducted using ANY particulate sampling
device that conforms to the ISO definition i.e.
collects dust according to the
particle collection efficiency curve specified in
the ISO standard.
NEW SKC SAMPLERS:
TO MEET SPECS IN ISO 7708
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Impaction based PPI
samplers also available
for respirable dust.
Designed to precisely
match the
ISO/CEN/ACGIH/NIOSH
criteria.
Available in reusable or
disposable options.
SKC RESPIRABLE PPI:
FLOWRATE OPTIONS

2 L/min: 225-385

8 L/min: 225-384

Single-use, disposable
PPI models are
available for use at
either 2, 4, or 8 L/min.
Available empty or preloaded with filters.
A calibration adapter is
available for disposable
models.
4 L/min: 225-387
WHY THE HIGHER FLOW RATE
RESPIRABLE PPI SAMPLERS?
NIOSH reported that for a working environment with
an airborne concentration of respirable silica near
the current TLV of 25 ug/m3, the amount of sample
collected with current respirable dust samplers (at
typical flow rates of 2 L/min ) might not be enough
for quantitative analysis. (Harper, et. al. Ann. Occup. Hyg., 2010.)
PUMP PARTNERS:
HIGH FLOW PPI SAMPLERS
Respirable PPI

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4 L/min model can be
partnered with SKC
XR5000.
8 L/min model can be
partnered with the SKC
Leland Legacy pump.
PPI SAMPLER PERFORMANCE
COMPARED TO CRITERIA
100
Penetration, P, %
75
Respirable PPI, 2.0 L/min
50
Respirable PPI, 4.0 L/min
Respirable PPI, 8.0 L/min
ISO/CEN Respirable Criteria
25
0
1
5
Aerodynamic Particle Diameter, da, mm
10
PPI DATA:
OSHA DOCKET
SKC submitted comments to the OSHA
docket on the silica NPRM with data on
the PPI. (Electronic copies are available upon
request).
 The data which was published in the Journal
of Physics shows that the collection efficiency of
the PPI is a close match to the ISO standard
and the bias is more acceptable than the HD
cyclone (listed in the NPRM.)

SAMPLE TIMES REQUIRED
FOR QUANTIFICATION BY LAB
4+ HOURS
2+ HOURS
PER OSHA NPRM
Using respirable dust
samplers at flows of
approx. 2-4 L/min in
workplace concentrations
of quartz down to the
proposed action level of
25 ug/m3. (TLV levels)
PER SKC SCIENTISTS
Using respirable dust
samplers at flows of
8 L/min at these same
workplace concentrations.
ANALYTICAL METHODS:
SENSITIVITY CONCERNS

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U.S. OSHA concluded that both X-Ray
diffraction (XRD) and Infrared Spectroscopy
(IR) methods are sensitive enough to quantify
silica in workplace concentrations at the
proposed PEL and action levels. (But
precision is lacking at 25 ug/m3)
Visible absorption spectrophometry (VIS)
methods are NOT sensitive enough.
THANK YOU FOR YOUR
ATTENTION!
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