Instrumentation and control

1. 8
Environmental
Measurement
U.S. Environmental Protection Agency (EPA) . . . . . . . . . . . . . . . . . 241
National Ambient Air Quality Standards (NAAQS) . . . . . . . . . . . . 241
Air Quality Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
Airborne Contaminants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
• Liquids, Vapors, Aerosols, Sea Salt Mist
• Table Classifying Chemically Active Contaminants: Liquid
Aerosols
• Solid Contaminants
• Table Classifying Airborne Particulates
• Gas Contaminants
• Table Classifying Reactive Environments & Terminology

2. U.S. Environmental Protection Agency
The U.S. Environmental Protection Agency is perhaps the single best
source of information regarding environmental rules, regulations and
topics. EPA’s mission is to protect human health and the environment.
Readers seeking EPA-related information are encouraged to go to EPA’s
web site:
http://www.epa.gov
All topics covered by EPA are listed alphabetically – with links to locate
detailed information – at:
http://www.epa.gov/ebtpages/alphabet.html
U.S. National Ambient Air Quality Standards
The U.S. Clean Air Act, last amended in 1990, requires the U.S. Envi-ronmental
Protection Agency (EPA) to set National Ambient Air Quality
Standards (NAAQS) for pollutants considered harmful to public health
and the environment. The Clean Air Act established two types of
national air quality standards. Primary standards set limits to protect
public health, including the health of “sensitive” populations such as
asthmatics, children, and the elderly. Secondary standards set limits to
protect public welfare, including protection against decreased visibility,
damage to animals, crops, vegetation, and buildings. The EPA Office of
Air Quality Planning and Standards (OAQPS) established National
Ambient Air Quality Standards for seven principal pollutants, called
“criteria” pollutants. They are listed in the following table. Units of
measure for the standards are parts per million (ppm) by volume, mil-ligrams
per cubic meter of air (mg/m3), and micrograms per cubic
meter of air (μg/m3).
Chapter 8/Environmental Measurement 241

3. 242 ISA Handbook of Measurement Equations and Tables
National Ambient Air Quality Standards
Pollutant Primary
Standards
Averaging
Times
1 Not to be exceeded more than once per year.
2 To attain this standard, the expected annual arithmetic mean PM10 concentration at each monitor
within an area must not exceed 50 μg/m3.
3 To attain this standard, the 3-year average of the annual arithmetic mean PM2.5 concentrations from
single or multiple community-oriented monitors must not exceed 15.0 ug/m3.
4 To attain this standard, the 3-year average of the 98th percentile of 24-hour concentrations at each pop-ulation-
oriented monitor within an area must not exceed 65 μg/m3.
5 To attain this standard, the 3-year average of the fourth-highest daily maximum 8-hour average ozone
concentrations measured at each monitor within an area over each year must not exceed 0.08 ppm.
6 (a) The standard is attained when the expected number of days per calendar year with maximum
hourly average concentrations above 0.12 ppm is <= 1.
(b) The 1-hour NAAQS will no longer apply to an area one year after the effective date of the designa-tion
of that area for the 8-hour ozone NAAQS. The effective designation date for most areas is June 15,
2004. (40 CFR 50.9; see Federal Register of April 30, 2004 [69 FR 23996].
Secondary
Standards
Carbon
Monoxide
9 ppm (10 mg/m3) 8-hour1 None
35 ppm (40 mg/m3) 1-hour1 None
Lead 1.5 μg/m3 Quarterly
Average
Same as Primary
Nitrogen
Dioxide
0.053 ppm
(100 μg/m3)
Annual
(Arithmetic Mean)
Same as Primary
Particulate
Matter (PM10)
50 μg/m3 Annual2
(Arith. Mean)
Same as Primary
150 ug/m3 24-hour1
Particulate
Matter (PM2.5)
15.0 μg/m3 Annual3
(Arith. Mean)
Same as Primary
65 μg/m3 24-hour4
Ozone 0.08 ppm 8-hour5 Same as Primary
0.12 ppm 1-hour6 Same as Primary
Sulfur Oxides 0.03 ppm Annual
(Arith. Mean)
———
0.14 ppm 24-hour1 ———
——— 3-hour1 0.5 ppm
(1300 μg/m3)

4. Chapter 8/Environmental Measurement 243
Air Quality Index
The Air Quality Index (AQI) is an index for reporting daily air quality. It
tells how clean or polluted the air is, and what associated health effects
might be a concern. The AQI focuses on why health effects might be
experienced within a few hours or days after breathing polluted air. EPA
calculates the AQI for five major air pollutants regulated by the Clean
Air Act: ground-level ozone, particle pollution (also known as particulate
matter), carbon monoxide, sulfur dioxide, and nitrogen dioxide. An AQI
value of 100 generally corresponds to the national air quality standard
for the pollutant, which is the level EPA has set to protect public health.
AQI values below 100 are generally thought of as satisfactory. When
AQI values are above 100, air quality is considered to be unhealthy — at
first for certain sensitive groups of people, then for everyone as AQI val-ues
get higher. To make it easier to understand, the AQI is divided into
six categories:
Air Quality Index
(AQI) Values
Levels of Health
Concern
Each category corresponds to a different level of health concern. The
six levels of health concern and what they mean are:
• “Good” The AQI value for your community is between 0 and 50. Air
quality is considered satisfactory, and air pollution poses little or no
risk.
• “Moderate” The AQI for your community is between 51 and 100.
Air quality is acceptable; however, for some pollutants there may be
a moderate health concern for a very small number of people. For
example, people who are unusually sensitive to ozone may experi-ence
respiratory symptoms.
Colors
When the AQI
is in this range:
...air quality
conditions are:
...as symbolized
by this color:
0 to 50 Good Green
51 to 100 Moderate Yellow
101 to 150 Unhealthy for
Sensitive Groups
Orange
151 to 200 Unhealthy Red
201 to 300 Very Unhealthy Purple
301 to 500 Hazardous Maroon

5. 244 ISA Handbook of Measurement Equations and Tables
• “Unhealthy for Sensitive Groups” When AQI values are between
101 and 150, members of sensitive groups may experience health
effects. This means they are likely to be affected at lower levels than
the general public. For example, people with lung disease are at
greater risk from exposure to ozone, while people with either lung
disease or heart disease are at greater risk from exposure to particle
pollution. The general public is not likely to be affected when the AQI
is in this range.
• “Unhealthy” Everyone may begin to experience health effects
when AQI values are between 151 and 200. Members of sensitive
groups may experience more serious health effects.
• “Very Unhealthy” AQI values between 201 and 300 trigger a health
alert, meaning everyone may experience more serious health effects.
• “Hazardous” AQI values over 300 trigger health warnings of emer-gency
conditions. The entire population is more likely to be affected.

6. Chapter 8/Environmental Measurement 245
Airborne Contaminants
An ISA standard, ISA-71.04-1985, Environmental Conditions for Process
Measurement and Control Systems: Airborne Contaminants, classifies
airborne contaminants that may affect process measurement and con-trol
instruments. The standard establishes airborne contaminant
classes for fixed (non-mobile) installations during normal operation
(non-emergency conditions) or during transportation and storage. The
classification consists of a class contaminant letter followed by a sever-ity
identification numeral.
Airborne Contaminants — Liquids, Vapors, Aerosols, Sea Salt Mist
Liquids — This refers to liquids that will corrode unprotected equip-ment
and are typically transported to the equipment by condensation,
rain, splashing liquids, or cleaning fluids sprayed from hoses. The
majority of these are not classified, but should be specified to the man-ufacturers
of equipment by special classification LX.
Vapors — Solvents sometimes occur as vapors which may condense
and form puddles that become corrosive to instruments and controls.
Aerosols — Aerosols are liquids carried in gas or air in the form of
small droplets generating mists. Aerosols can vary in composition and
are a major source of chemical contamination to equipment.
Sea Salt Mist — Class LC1: Inland more than 0.5 km from shore;
Class LC2: Inland less than 0.5 km from shore; Class LC3: Offshore
installations (oil rigs, etc.)

7. 246 ISA Handbook of Measurement Equations and Tables
Classification of Chemically Active Contaminants:
Liquid Aerosols (Measured in μg/kg except as specified)
Severity
Level 1
Severity
Level 2
*For example, trichloroethylene (CHClCCl2)
NOTES:
1.0 μg/kg = 1.0 part per billion (p/109)
T.B.S. = To Be Specified
< is defined as “less than”
> is defined as “more than”
≥ is defined as “greater than or equal to”
Severity
Level 3
Severity
Level X
(special)
Contaminant Class Value Value Value Value
Vapors* LA < 1.0 < 5.0 < 20.0 ≥ 20.0
Oils LB < 5.0 < 50.0 < 100.0 ≥ 100.0
Sea salt mist LC
More than
0.5 km
inland
Within 0.5
km inland
Offshore
installation T.B.S.
Special T.B.S. LX T.B.S. T.B.S. T.B.S. T.B.S.

8. Chapter 8/Environmental Measurement 247
Airborne Contaminants — Solids
Dust is a universal contaminant and is a cause of environmentally
induced equipment failures. Failure modes may be mechanical, chemi-cal,
electrical, thermal, or magnetic. To maximize equipment reliability
and life, every effort should be made to minimize exposure to airborne
particulates. The sensitivity of control equipment to different types of
particulates varies widely. In the table below, solid particulates are
classified by size. The environment should be described in terms of
concentration severity level for each class, Classes SA through SD.
Classification of Airborne Particulates
Severity Level (concentration
measured in μg/m3
Particle
Size
Class 1 2 3 X
> 1 mm SA < 1000 < 5000 < 10,000 ≥ 10,000
100 μm to
1000 μm SB < 500 < 3000 < 5000 ≥ 5000
1 μm to
100 μm SC < 70 < 200 < 350 ≥ 350
< 1 μm SD < 70 < 200 < 350 ≥ 350
Notes:
μm = micrometer = 0.001 millimeter
μg/m3 = micrograms per cubic meter

9. 248 ISA Handbook of Measurement Equations and Tables
Airborne Contaminants — Gases
Two methods have been used for environmental characterization. One is
a direct measure of selected gaseous air pollutants. The other, which can
be termed “reactivity monitoring,” provides a quantitative measure of the
overall corrosion potential of an environment. High values will confirm
that a severe environment exists. The reverse, however, is not necessarily
true. Industrial environments may contain a complex mixture of contami-nants
that interact to greatly accelerate (or retard) the corrosive action of
individual gas species. To avoid these practical difficulties, the nature of
industrial environments is defined in terms of the rate at which they react
with copper. Copper has been selected as the coupon material because
data exists which correlates copper film formation with reactive (corro-sive)
environments. Four levels of corrosion severity are established in
Table 3. Concentration levels of some gases that contribute to these reac-tivity
rates are also cited:
Severity level G1: Mild — An environment sufficiently well-controlled
such that corrosion is not a factor in determining equipment reliability.
Severity level G2: Moderate — An environment in which the effects
of corrosion are measurable and may be a factor in determining equip-ment
reliability.
Severity level G3: Harsh — An environment in which there is a high
probability that corrosive attack will occur. These harsh levels should
prompt further evaluation resulting in environmental controls or spe-cially
designed and packaged equipment.
Severity level GX: Severe — An environment in which only specially
designed and packaged equipment would be expected to survive.
Specifications for equipment in this class are a matter of negotiation
between user and supplier.

10. Classification of Reactive Environments & Terminology
* Measured in angstroms after one month’s exposure.
† mm3
/m3 (cubic millimeters per cubic meter) parts per billion aver-age
for test period for the gases in Groups A and B.
‡ The Group A contaminants often occur together and the reactivity lev-els
include the synergistic effects of these contaminants.
§ The synergistic effects of Group B contaminants are not known at
this time.
Chapter 8/Environmental Measurement 249
The gas concentration levels shown below are provided for reference pur-poses.
They are believed to approximate the Copper Reactivity Levels stated
above, providing the relative humidity is less than 50%. For a given gas con-centration,
the Severity Level (and Copper Reactivity Level) can be expected
to be increased by one level for each 10% increase in relative humidity above
50% or for a relative humidity rate of change greater than 6% per hour.
Reactive
Species†,‡
Contaminant Gas Concentration
Group A H2S < 3 < 10 < 50 ≥ 50
SO2,
SO3
<10 < 100 < 300 ≥ 300
Cl2 < 1 < 2 < 10 ≥ 10
NOx < 50 < 125 < 1250 ≥ 1250
Group B§ HF < 1 < 2 < 10 ≥ 10
NH3 < 500 < 10,000 < 25,000 25,000
O3 < 2 < 25 < 100 100
Severity Level G1
Mild
G2
Moderate
G3
Harsh
G4
Severe
Copper
Reactivity Level
(in angstroms)*
< 300 < 1000 < 2000 ≥ 2000