Air Monitoring - Brownfields Toolbox
Download
Report
Transcript Air Monitoring - Brownfields Toolbox
Air Monitoring
Instructional Goal:
Enable participants to recognize the
value of direct-reading instruments in
providing immediate air concentration
results at a hazardous waste site.
1
1
Sampling Methods
Area
sampling
involves placing collection devices within
designated areas and operating them over
specific periods of time.
Personal
sampling
involves collecting samples from within the
breathing zone of an individual, sometimes
by the individual wearing a sampling device.
2
Instantaneous Sample
are collected over brief periods of time
grab-type sample
examines stable contaminant
concentrations or peak levels of short
duration.
require highly sensitive analytical methods
due to the small sample volume
3
Air Monitoring Data is used to
4
assess health risks
determine location where PPE must be worn
and correct PPE to wear
determine actual or potential effects on the
environment
select actions to mitigate the hazards
determine the effectiveness of
decontamination activities
Sampling System
sampling instrument or system chosen
depends on a number of factors:
instrument or system efficiency
operational reliability
ease of use and portability
availability of the instrument and
component parts
information or analysis desired
calibration requirements
5
Air Monitoring Instruments
must be
portable
easy
6
and rugged
to operate
Air Monitoring Instruments
must be Inherently Safe
explosion-proof
intrinsically
purged
7
safe
Air Monitoring Instruments must
give Reliable and Useful Results
Response
time
is the length of time the monitor takes from
when it "senses" a contaminant until it
generates data. For direct-reading
instruments, response times may range
from a few seconds to several minutes.
8
Air Monitoring Instruments must
give Reliable and Useful Results
Sensitivity
defined as the ability of an instrument to
accurately measure changes in
concentration. Sensitive instruments can
detect small changes in concentration.
It is important to use an instrument with
an operating range that will measure the
ambient concentrations on-site.
9
Air Monitoring Instruments must
give Reliable and Useful Results
Selectivity
the ability of an instrument to detect and
measure a specific chemical or group of
similar chemicals.
Interferences from other chemicals can
affect the accuracy of the instrument
reading by producing a similar response.
10
Air Monitoring Instruments must
give Reliable and Useful Results
Accuracy
the relationship between a true value (i.e.,
the actual concentration of a contaminant)
and the instrument reading.
11
Air Monitoring Instruments must
give Reliable and Useful Results
Precision
a statistical measurement of
an instrument's ability to
reproduce a reading.
When an instrument does not
receive routine maintenance
the precision of the readings
may change (become more
random) this can affect the
amount of error in the data
12 collected.
Bench Calibration
follow
manufacturer’s directions
for calibration to ensure accurate
field data
use standard sample of known
concentration for calibration
adjust the instrument read-out so
that it corresponds to the actual
concentration
13
Monitoring Equipment
Direct-Read
Instruments
oxygen availability monitor
combustibility monitor
toxic atmosphere monitor
radiation monitor
14
Oxygen Indicators
20.8% O2 is normal air
at and below 19.5% O2 in air, O2 deficient
either displaced by another gas
or consumed by combustion or reaction
> 23% O2 in air, increased risk of
combustion (possible oxidizer present)
15
Combustible Gas Monitor
measures concentration of flammable
vapor or gas in air
reads in % Lower Explosion Limit (LEL)
read out is relative to the calibration
gas; therefore, may not show actual %
of LEL
for use only in normal oxygen
atmospheres
16
Flammable
Range
LEL
0% 5%
0%
0%
10%
Action Level
17
UEL
15%
METHANE
100%
5%
LEL
METER READING % LEL
Relative Response CGI Meter
methane
100%
80%
pentane
60%
40%
xylene
20%
0%
0%
50%
ACTUAL % LEL
100%
% LEL Policy
The employer will issue work
permits when the % LEL is from 010% LEL.
When the LEL exceeds 10%,
special approval is required in
order for a work permit to be
issued.
For all confined space entry
permits, a 0% LEL is required.
19
Toxic Atmosphere Monitors
20
20
Colorimetric Indicator Tubes
Features
glass tube with
indicating chemical
chemical specific
contaminated air
pumped in at predetermined rate
Pre-filter
Cotton Plug
21
DETECTOR TUBE
Color Change
Indicating Chemical
on Silica Gel
Limitations
other chemicals may
interfere with result
poor accuracy and
precision
affected by temperature
and humidity
interpretations vary
time consuming - 1 to 30
minutes per tube
Cotton Plug
Photoionization Detector
Features
Nonspecific gas and vapor
detection for organics and some
inorganics
Sensitivity is related to the
ionization potential of
compound
Portable with remote sensing
capabilities
Response time of 90% in less
than 3 seconds
More sensitive to aromatic and
unsaturated compounds than
the flame ionization detector
22
Limitations
Does not monitor for
specific gases or vapors
Cannot detect Hydrogen
cyanide or methane
Cannot detect some
chlorinated organics
High humidity and
precipitate will negatively
affect meter response
Photoionization detectors
are calibrated to a single
chemical
Flame Ionization Detector
Features
Nonspecific total
hydrocarbon analyzer
Most sensitive to
saturated hydrocarbons
(alkanes), and
unsaturated hydrocarbon
(alkenes)
Portable with remote
sensing probe
Response time of 90% in
2 seconds
23
Limitations
Not suitable for inoganic gases
(e.g. chlorine, hydrogen
cyanide, ammonia)
Less sensitive to unsaturated
compounds than PID
Can not use in the presence of
a flammable gas (ignition
source)
Substances that contain
substituted functional groups
(-OH) and (-Cl) reduce the
detector's sensitivity
Aerosol Monitors
Solids
and liquids can become
suspended in air
light scatter detector
piezoelectric crystal mass monitor
beta attenuation
Total
particulate amount
Type not determined
24
Sample Problem
Suppose prior analysis has established that
the dust at a certain site contains 5 percent
lead and 1 percent arsenic. During
subsequent monitoring, the concentration of
dust is found to be 2mg/m3.
(% of each)
100
25
X
amount of dust= conc of each
present in air
Answer
The concentration of lead and arsenic,
therefore, are calculated to be 0.1 mg/m3
and 0.02 mg/m3 respectively:
0.05 x 2 mg/m3 = 0.1 mg/m3 lead
0.01 x 2 mg/m3 = 0.02 mg/m3 arsenic
26
Combination Instruments
flammable
gas and O2
trimeters
four
27
gas meters
Radiation Monitoring
Alpha
Proportion Counters
Scintillation Counters
Beta and Gamma
Geiger-Mueller Counters
28