What is a Confined Space Hazard Assessment and Control Program?
To manage the risks associated with working in confined
spaces, a Confined Space Hazard Assessment and Control Program should
be developed and implemented. A Confined Space Hazard Assessment and
Control Program, specific for the work being conducted, should be
written for work in each and every confined space.
A Confined Space Hazard Assessment and Control Program should include the following:
A Confined Space Hazard Assessment and Control Program should include the following:
- Description of roles and responsibilities of each person or party (e.g., employer, supervisor, workers, attendant, and emergency response team).
- Advice on how to identify confined spaces.
- The identification and assessment of all potential hazards that may exist at the beginning of the work as well as those that may develop because of the work activities.
- A plan to eliminate or control all identified hazards.
- Training program for all the workers that will enter into the confined spaces.
- The establishment of an entry permit system for each entry into a confined space.
- Development of an emergency plan complete with training and equipment in case an unforeseen situation occurs.
- An emergency response system.
- Program review whenever there is a change in circumstances or at least annually, to identify program weaknesses and make any necessary changes to the program.
- Record and documentation control.
What is an Entry Permit System?
An Entry Permit is an administrative tool used to
document the completion of a hazard assessment for each confined space
entry. Someone fully trained and experienced in confined space work
should complete the Entry Permit.
Before entering a confined space, an entry permit should be written. It should contain at least the following information:
Before entering a confined space, an entry permit should be written. It should contain at least the following information:
- The length of time the permit is valid for.
- The name(s) of the worker(s) that are authorized to enter the confined space.
- The name(s) of the attendant(s) (safety watch) and/or supervisor.
- The location and description of the confined space.
- The work that is to be done in the confined space.
- Possible hazards that may be encountered inside and outside the space.
- Possible hazards that may develop during the work activity.
- The date and time of entry into the confined space and the anticipated time of exit.
- The details of any atmospheric testing done of the confined space - when, where, results, date monitoring equipment was last calibrated. Ideally, calibration would be done just before each use. If this is not possible, follow the equipment manufacturers guidelines for frequency of calibration.
- Hazard control measures, including the use of mechanical ventilation and other protective equipment needed and any other precautions that will be followed by every worker who is going to enter the confined space.
- Means of communication between the persons working in the confined space and the attendant.
- Emergency plan, and the protective equipment and emergency equipment to be used by any person who takes part in a rescue or responds to other emergency situations in the confined space
- A signature of a worker who did the confined space air testing. The signature on the permit would indicate that adequate precautions are being taken to control the anticipated hazards.
- Authorization signature by the supervisor certifying that the space has been properly evaluated, prepared, and it is safe for entry and work.
What should happen when work is being done in a confined space?
There should be warning signs to prevent unauthorized entry to the confined space.
Anyone
working in a confined space must be constantly alert for any changing
conditions within the confined space. In the event of an alarm from
monitoring equipment or any other indication of danger, workers should
immediately leave the confined space.
Another worker, the attendant (also knowns as the Safety Watch or Standby), is posted outside the confined space and continuously monitors the workers inside the confined space. The Safety Watch has the following duties:
No confined space should be closed off until it has been verified that no person is inside it.
After exiting the confined space, the time of exit should be noted on the entry permit.
Another worker, the attendant (also knowns as the Safety Watch or Standby), is posted outside the confined space and continuously monitors the workers inside the confined space. The Safety Watch has the following duties:
- Understands the nature of the hazards that may be found inside the particular confined space and can recognize signs, symptoms and behavioural effects that workers in the confined space could experience.
- Monitors the confined space and surrounding area and is on the look out for dangerous conditions.
- Remains outside the confined space and does no other work which may interfere with their primary duty of monitoring the workers inside the confined space.
- Maintains constant two-way communication with the workers in the confined space.
- Orders the immediate evacuation if a potential hazard, not already controlled for, is detected.
- Calls for emergency assistance immediately if an emergency develops.
- Is immediately available to provide non-entry emergency assistance when needed.
- Can provide entry rescue only after the most stringent precautions are taken and another Safety Watch is immediately available.
No confined space should be closed off until it has been verified that no person is inside it.
After exiting the confined space, the time of exit should be noted on the entry permit.
What are some emergency response precautions?
If a situation arises where there is a hazardous
condition and the worker does not leave or is unable to leave the
confined space, rescue procedures should be begin immediately.
The Safety Watch is qualified in confined spaces rescue procedures and will be available immediately outside the confined space to provide emergency assistance if needed. The Safety Watch should be familiar with the structural design of the confined space. The Safety Watch is in constant communication with the worker inside the confined space and will:
The
detailed plan for emergency response to an injury or other emergency
within the confined space should be described in detail in the Confined
Space Hazard Assessment and Control Program.
Rescue the victims from outside of the confined space, if possible. No other worker should enter a confined space to attempt a rescue unless that worker is fully trained in the rescue procedures and is wearing the appropriate personal protective equipment. More than 60% of deaths in confined spaces are would-be rescuers, who are not fully trained and adequately equipped.
Another worker qualified in confined spaces rescue procedures must be present outside the confined space before the first rescuer enters the confined space. Do not use the same air as the confined space workers you are rescuing. Wear SCBA (self contained breathing apparatus) or supplied air respirator with an escape bottle.
The Safety Watch is qualified in confined spaces rescue procedures and will be available immediately outside the confined space to provide emergency assistance if needed. The Safety Watch should be familiar with the structural design of the confined space. The Safety Watch is in constant communication with the worker inside the confined space and will:
- Have an alarm for calling for help.
- Have all required rescue equipment (for example, safety harnesses, lifting equipment, a lifeline) immediately available and be trained in its use.
- Hold a basic first aid certificate.
- Can do Cardiopulmonary Resuscitation (CPR).
Rescue the victims from outside of the confined space, if possible. No other worker should enter a confined space to attempt a rescue unless that worker is fully trained in the rescue procedures and is wearing the appropriate personal protective equipment. More than 60% of deaths in confined spaces are would-be rescuers, who are not fully trained and adequately equipped.
Another worker qualified in confined spaces rescue procedures must be present outside the confined space before the first rescuer enters the confined space. Do not use the same air as the confined space workers you are rescuing. Wear SCBA (self contained breathing apparatus) or supplied air respirator with an escape bottle.
Is worker training important?
Yes, appropriate training is extremely important to
working safely in confined spaces. Hands-on training should be an
essential part of the confined space training.
Every worker that enters a confined space must be fully trained on the following:
Every worker that enters a confined space must be fully trained on the following:
- Recognition and identification of potential hazards associated with the confined spaces that will be entered.
- Evaluation and control procedures for the identified or potential hazards.
- Set-up, use and limitations of all equipment such as emergency equipment, ventilation equipment (blowers), hazardous energy control, isolation and lockout equipment, and air quality monitors (e.g., Oxygen/combustible meters) that will be used while in the confined space.
- Set-up, use and limitations of all personal protective equipment (e.g., full-body harness, respirators) that the worker will be using while in the confined space.
- All safe work procedures for entering the confined space as outlined in the employer's Confined Space Hazard Assessment Program.
- Procedures to follow in the event of a situation developing that could present additional risk to the worker or an emergency.
- The specific work to be done while in the confined space.
- To work in a manner that will not endanger lives.
December 29th, 2016
Converting Atmospheric Pollutant Concentrations: from mg/m3 to ppmv
The conversion factor depends on the temperature at which you want the conversion (usually about 20 to 25 degrees Centigrade). At an ambient pressure of 1 atmosphere, the general equation is:
|
where:
|
ppmv
mg/m3 MW °C |
=
= = = |
ppm by volume
(i.e., volume of gaseous pollutant per 106 volumes of ambient air)
milligrams of gaseous pollutant per cubic meter of ambient air molecular weight of the gaseous pollutant ambient air temperature in degrees Centigrade |
As an example, for gaseous pollutant NOx, convert 20 mg/m3 to ppmv at 25 °C:
ppmv = (20)(273.15 + 25) / (12.187)(46.01) = 10.6
where: 46.01 = molecular weight of NO2 (i.e., NOx expressed as nitrogen dioxide)
NOTES:
(1) The pollution laws and regulations in the United States typically reference their pollutant limits to an ambient temperature of 20 to 25 °C as noted above. However, in other nations, the reference ambient temperature for pollutant limits may be 0 °C or other values.
(2) 1 percent by volume = 10,000 ppmv (i.e., parts per million by volume).
(3) For all practical purposes, degrees Centigrade and degrees Celsius are synonymous.
Converting Atmospheric Pollutant Concentrations: from ppmv to mg/m3
The conversion factor depends on the temperature at which you want the conversion (usually about 20 to 25 degrees Centigrade). At an ambient pressure of 1 atmosphere, the general equation is:
|
where:
|
mg/m3
ppmv MW °C |
=
= = = |
milligrams of
gaseous pollutant per cubic meter of ambient air
ppm by volume (i.e., volume of gaseous pollutant per 106 volumes of ambient air) molecular weight of the gaseous pollutant ambient air temperature in degrees Centigrade |
As an example, for gaseous pollutant NOx, convert 20 ppmv to mg/m3 at 25 °C:
mg/m3 = (20)(12.187)(46.01) / (273.15 + 25) = 37.6
where: 46.01 = molecular weight of NO2 (i.e., NOx expressed as nitrogen dioxide)
NOTES:
(1) The pollution laws and regulations in the United States typically reference their pollutant limits to an ambient temperature of 20 to 25 °C as noted above. However, in other nations, the reference ambient temperature for pollutant limits may be 0 °C or other values.
(2) 1 percent by volume = 10,000 ppmv (i.e., parts per million by volume).
(3) For all practical purposes, degrees Centigrade and degrees Celsius are synonymous.
Effect of Altitude on Atmospheric Pollutant Concentrations:
Atmospheric pollutant concentrations expressed as mass per unit volume of atmospheric air (e.g., mg/m3, ug/m3, etc.) at sea level will decrease with increasing altitude because the atmospheric pressure decreases with increasing altitude.
The change of atmospheric pressure with altitude can be obtained from this equation:
|
Given an atmospheric pollutant concentration at an atmospheric pressure of 1 atmosphere (i.e., at sea level altitude), the concentration at other altitudes can be obtained from this equation:
|
where:
|
a
Pa C Ca |
=
= = = |
altitude, in 100's
of meters
atmospheric pressure at altitude a, in atmospheres concentration at sea level altitude, in mass per unit volume concentration at altitude a, in mass per unit volume |
As an example, given a concentration of 260 mg/m3 at sea level, calculate the equivalent concentration at an altitude of 1,800 meters:
Ca = (260)(0.987718) = 208 mg/m3 at 1,800 meters altitude
Calculation Of Gas Densities:
The following equation for the density of a gas in pounds per cubic foot is derived from the ideal gas law and the applicable universal gas constant:
|
The following equations for the density of a gas in kilograms per cubic meter are also derived from the ideal gas law and the applicable universal gas constants ... one of the equations uses the absolute pressure expressed in atmospheres and the other uses the absolute pressure expressed in kilopascals:
|
|
where:
|
Z
MW psia atm kPa 1 atm °R °K °F °C |
= gas
compressibility factor at the given temperature and pressure
(dimensionless)
= molecular weight of the gas = absolute pressure in pounds per square inch = absolute pressure in atmospheres = absolute pressure in kilopascals = 14.696 psia = 101.325 kPa = absolute temperature of the gas in degrees Rankine = 459.67 + °F = absolute temperature of the gas in degrees Kelvin = 273.15 + °C = degrees Fahrenheit = ( 1.8 ) ( °C ) + 32 = degrees Centigrade = ( °F - 32 ) / 1.8 |
The numbers 10.73, 0.082057, and 8.3144 are all the universal gas law constant expressed in the applicable units for each of the above equations. For all practical purposes, degrees Centigrade and degrees Celsius are synonymous. Also, in many cases, it may be assumed that the ideal gas law applies and thus Z may be taken to be 1.00.
The technical literature can be very confusing because many authors fail to explain whether they are using the universal gas law constant R which applies to any ideal gas or whether they are using the gas law constant Rs which only applies to a specific individual gas. The relationship between the two constants is Rs = R / (MW).
Standard Conditions For Gas Volumes:
A normal cubic meter (Nm3) is the metric expression of gas volume at standard conditions and it is usually defined as being measured at 0 °C and 1 atmosphere of pressure.
A standard cubic foot (scf) is the USA expression of gas volume at standard conditions and it is very often defined as being measured at 60 °F and 1 atmosphere of pressure. There are other definitions of standard gas conditions used in the USA besides 60 °F and 1 atmosphere, but that is the most common one ... and it is very widely used in the oil, gas and hydrocarbon processing industries.
That being understood:
|
Gas Volume Conversions:
To convert air or other gas volumes from one pressure (P1) and temperature (T1) to another pressure (P2) and temperature (T1), use the following equation:
|
where:
|
Z
1 and Z 2
V1 and V2 P1 and P2 T1 and T2 °R °K °F °C |
= gas
compressibility factors (which are non-dimensional)
= gas volumes in the same dimensional units = absolute pressures in the same dimensional units = absolute temperatures in the same units (either degrees °R or degrees °K ) = absolute temperature in degrees Rankine = 459.67 + °F = absolute temperature in degrees Kelvin = 273.15 + °C = degrees Fahrenheit = ( 1.8 ) ( °C ) + 32 = degrees Centigrade = ( °F - 32 ) / 1.8 |
For all practical purposes, degrees Centigrade and degrees Celsius are synonymous. Also, in many cases, it may be assumed that the ideal gas law applies and thus Z may be taken to be 1.00.
Definition Of The Pasquill Stability Classes:
The amount of turbulence in the ambient air has a major effect upon the rise and dispersion of air pollutant plumes. The amount of turbulence can be categorized into defined increments or "stability classes". The most commonly used categories are the Pasquill stability classes A, B, C, D, E, and F. Class A denotes the most unstable or most turbulent conditions and Class F denotes the most stable or least turbulent conditions.
The Pasquill stability classes are presented below as they are defined by the prevailing meteorological conditions of: (a) surface windspeed measured at 10 meters above ground level and (b) day-time incoming solar radiation or the night-time percentage of cloud cover.
|
Surface
Windspeed |
Daytime
Incoming Solar Radiation |
Night-time
Cloud Cover |
||||
|
m/s
|
mi/hr
|
Strong
|
Moderate
|
Slight
|
> 50%
|
< 50%
|
|
<2
|
<5
|
A
|
A-B
|
B
|
E
|
F
|
|
2-3
|
5-7
|
A-B
|
B
|
C
|
E
|
F
|
|
3-5
|
7-11
|
B
|
B-C
|
C
|
D
|
E
|
|
5-6
|
11-13
|
C
|
C-D
|
D
|
D
|
D
|
|
>6
|
>13
|
C
|
D
|
D
|
D
|
D
|
|
Note: Class D applies to
heavily overcast skies, at any windspeed day or night.
|
||||||
NOTES:
(1) m/s = meters per second
(2) mi/hr = statute miles per hour
Pressure Conversions:
Atmospheric pressures may be expressed in a number of different units. The following table provides the conversions between six of the most commonly used units of pressure. Here are some examples as read from the table:
(1) 1 atmosphere = 14.696 psi or 101.325 kPa
(2) 1 bar = 0.986923 atmospheres or 750.0616 mm Hg
(3) 1 psi = 6.894733 kPa or 51.71475 mm Hg
|
|
atm
|
psi
|
kPa
|
bar
|
mm Hg
|
kg/cm2
|
|
1
atm =
|
1
|
14.696
|
101.325
|
1.01325
|
760
|
1.033228
|
|
1
psi =
|
0.068046
|
1
|
6.894733
|
0.068947
|
51.71475
|
0.070307
|
|
1
kPa =
|
0.009869
|
0.145038
|
1
|
0.010000
|
7.500617
|
0.010197
|
|
1
bar =
|
0.986923
|
14.50382
|
100.0000
|
1
|
750.0616
|
1.019716
|
|
1
mm Hg =
|
0.001316
|
0.019337
|
0.133322
|
0.001333
|
1
|
0.001360
|
|
1
kg/cm2 =
|
0.967841
|
14.22339
|
98.0665
|
0.980665
|
735.559
|
1
|
Although not included in the above table:
• 1 atmosphere of pressure = 33.90 feet of water = 10.33 meters of water
• 1 mm Hg = 1 torr
Notes:
atm = absolute pressure, in atmospheres
psi = absolute pressure, in pounds per square inch
kPa = absolute pressure, in kilopascals
bar = absolute pressure, in bars
mm Hg = absolute pressure, in millimeters of Mercury
kg/cm2 = absolute pressure, in kilograms per square centimeter
Effect of Altitude on Windspeeds:
The winds aloft generally have a higher velocity than the winds at ground level. In other words, at any given time and place, windspeed usually increases with altitude. The effect of altitude on windspeed involves two factors:
- the degree of turbulent mixing prevailing in the atmosphere at the given time and place, as characterized by the Pasquill stability class
- the terrain's surface area roughness, which induces surface friction at the given place
It has generally been agreed that the effect of
altitude on windspeed is logarithmic and can be expressed as:
|
where:
|
uz
ug hz hg n |
=
= = = = |
wind velocity at
height z
wind velocity at ground station height height z ground station height (usually 10 meters) : a function of the Pasquill stability class and the terrain type (see tables below) |
|
Table 1
For Use In Rural Terrain |
Table 2
For Use In Urban Terrain |
||
|
Stability
A B C D E F |
Exponent n
0.10 0.15 0.20 0.25 0.25 0.30 |
Stability
A B C D E F |
Exponent n
0.15 0.15 0.20 0.25 0.40 0.60 |
As an example, given a windspeed of 5 m/s measured at 10 meters above the ground and a stability class of B in rural terrain, calculate the windspeed at 500 meters above ground:
uz = (5)(500/10)0.15 = 9 m/s
Converting Mass Flow Rates To Volumetric Flow Rates:
Gaseous emission flow rates (from process vents, combustion flue gases from furnaces or boilers, accidental gaseous releases, etc.) are often expressed in mass flow rates. To convert such mass flow rates to volumetric flow rates, first calculate the gas density (as explained in one of the sections above) using the actual temperature and pressure of the gaseous emission. Then use either of the following equations:
|
where:
|
ft3 / hr
lbs / hr lbs / ft3 |
=
= = |
gas volumetric flow
rate in cubic feet per hour
gas mass flow rate in pounds per hour gas density in pounds per cubic foot |
|
where:
|
m3 / hr
kg / hr kg / m3 |
=
= = |
gas volumetric flow
rate in cubic meters per hour
gas mass flow rate in kilograms per hour gas density in kilograms per cubic meter |
Note: When calculating the density of the gaseous emission, the actual pressure of the gaseous emission at the point where it exits from the source vent or flue gas stack is taken as 14.696 psia or 1 atmospere.
Windspeed Conversion Factors:
Meteorological data includes windspeeds which may be expressed as statute miles per hour, knots, or meters per second. Here are the conversion factors for those various expressions of windspeed:
|
|
|
Note:
1 statute mile = 5,280 feet = 1,609 meters
Return to TopCorrecting Concentrations to Reference Conditions in Regulated Emission Limits:
Many environmental protection agencies have issued regulations that limit the concentration of pollutants in gaseous emissions and define the reference conditions applicable to those concentration limits. For example, such a regulation might limit the concentration of NOx to 55 ppmv in a dry combustion exhaust gas corrected to 3 volume percent O2. As another example, a regulation might limit the concentration of particulate matter to 0.1 grain per standard cubic foot (i.e., scf) of dry exhaust gas corrected to 12 volume percent CO2.
A standard cubic foot of dry gas is often denoted as "dscf" or as "scfd". Likewise, a standard cubic meter of dry gas is often denoted as "dscm" or "scmd" by environmental agencies in the USA.
Correcting Concentrations to a Dry Basis:
If a gaseous emission sample is analyzed and found to contain water vapor and a pollutant concentration of X, then X should be designated as the "wet basis" pollutant concentration. The following equation can be used to correct the measured "wet basis" concentration to a "dry basis" concentration:
|
where:
|
w
|
=
|
fraction of the
emitted exhaust gas, by volume, which is water vapor
|
Thus, a wet basis concentration of 40 ppmv in an emitted gas containing 10 volume percent water vapor would have a dry basis concentration = ( 40 ) / ( 1 - 0.10 ) = 44.44 ppmv.
Correcting Concentrations to a Reference O2 Content in the Emitted Gas:
The following equation can be used to correct a measured pollutant concentration in an emitted gas (containing a measured O2 content) to an equivalent pollutant concentration in an emitted gas containing a specified reference amount of O2:
|
where:
|
Cr
Cm |
=
= |
corrected
concentration in dry emitted gas having the reference volume % O2
= r
measured concentration in dry emitted gas having the measured volume % O2 = m |
Thus, a measured nitrogen oxides (i.e., NOx) concentration of 45 ppmv (dry basis) in an emitted gas having 5 volume % O2 = ( 45 ) ( 20.9 - 3 ) / ( 20.9 - 5 ) = 50.7 ppmv (dry basis) when corrected to an emitted gas having a specified reference O2 content of 3 volume %.
Correcting Concentrations to a Reference CO2 Content in the Emitted Gas:
The following equation can be used to correct a measured pollutant concentration in an emitted gas (containing a measured CO2 content) to an equivalent pollutant concentration in an emitted gas containing a specified reference amount of CO2:
|
where:
|
Cr
Cm |
=
= |
corrected
concentration in dry emitted gas having the reference volume % CO2
= r
measured concentration in dry emitted gas having the measured volume % CO2 = m |
And thus, a measured particulate matter concentration of 0.1 grain per dscf in an emitted gas that has 8 volume % CO2 = ( 0.1 ) ( 12 / 8 ) = 0.15 grain per dscf when corrected to an emitted gas having a specified reference CO2 content of 12 volume %.
Notes:
-- Although ppmv and grains per dscf have been used in the above examples, you may use other concentrations such as ppbv (i.e., parts per billion by volume), volume percent, grams per dscm, etc.
-- 1 percent by volume = 10,000 ppmv (i.e., parts per million by volume).
-- Equation (1) above is from "40 CFR, Chapter I, Part 60, Appendix A-3, Test Method 4".
-- Equation (2) above is from "40 CFR, Chapter I, Part 60, Appendix B, Performance Spec. 2".
-- Equation (3) above is from "40 CFR, Chapter I, Part 60".
Exhaust Gas Generated From Combustion of Fuels:
It is often useful to have a good estimate of the amount of exhaust gas or flue gas generated by the combustion of a fuel and of the O2 and CO2 content of the gas. Here are some typical values:
|
Combustion Data:
|
Fuel
Gas
|
Fuel
Oil
|
Coal
|
|
Higher heating value, Btu /
scf
Higher heating value, Btu / gallon Higher heating value, Btu / pound Molecular weight Gravity, °API Carbon / hydrogen ratio by weight Weight % carbon Weight % hydrogen Weight % oxygen Weight % sulfur Weight % nitrogen Weight % ash Weight % moisture Excess combustion air, % Amount of wet exhaust gas, scf / MMBtu of fuel CO2 in wet exhaust gas, volume % O2 in wet exhaust gas, volume % Molecular weight of wet exhaust gas Amount of dry exhaust gas, scf / MMBtu of fuel CO2 in dry exhaust gas, volume % O2 in dry exhaust gas, volume % Molecular weight of dry exhaust gas |
1,093
18 12 11,600 8.8 2.0 27.7 9,510 10.8 2.5 29.9 |
150,000 15.5 8.1 15 11,930 12.4 2.6 29.0 10,600 14.0 2.9 30.4 |
8,020 47.9 3.4 10.8 0.9 0.6 6.0 30.4 20 13,985 13.5 3.3 29.0 12,130 15.5 3.8 30.8 |
Converting the Exhaust Gas Amounts to Other Units:
The amount of fuel combusted may be expressed in MMBtu, or in MMkcal, or in MW-hr ... and the amount of combustion exhaust gas may be expressed as standard cubic feet (scf) or as Normal cubic meters (Ncm or Nm3). These are the definitions and equivalents involved in converting the exhaust gas amounts from scf / MMBtu to other units:
(a) 1 MMBtu = 106 Btu
(b) 1 MMkcal = 106 kilogram-calories
(c) 1 MW-hr = 1 megawatt-hour = 106 watt-hours
(d) 1 MMBtu = 0.252 MMkcal = 0.293 MW-hr
(e) 1 MMkcal = 3.968 MMBtu = 1.163 MW-hr
(f) 1 MW-hr = 3.413 MMBtu = 0.860 MMkcal
(g) scf = standard cubic feet measured at 60 °F and atmospheric pressure
(h) Nm3 = Normal cubic meters measured at 0 °C and atmospheric pressure
(i) 1 Nm3 = 37.326 scf
These are the resulting conversions from scf / MMBtu to other units:
1 scf / MMBtu = 0.1063 Nm3/ MMkcal = 0.0914 Nm3/ MW-hr
Notes:
-- Reference temperatures (other than those above) are used to define standard cubic feet and Normal cubic meters, but those given above are widely used. As an example, the USA's Environmental Protection Agency uses 68 °F ( 20 °C ) as the reference temperature for both standard cubic feet ( scf ) and standard cubic meters ( scm ) ... whereas most of the oil and gas industries worldwide generally use 60 °F to define scf, and all of the metric nations use the term Normal m3 (rather than scm) with a reference temperature of 0 °C ( rather than 20 °C ) .
-- The dry and wet exhaust gas volumes given above differ somewhat from the U.S. EPA's corresponding F Factors ( see publication EPA-454/R-95-015, Revised ) because: ( a ) the EPA's F Factors are all at 0 % excess combustion air, ( b ) the EPA's reference temperature for scf is 68 °F rather the 60 °F used above, and ( c ) the fuel compositions that were used for the EPA's F Factors probably differ from those used above.
-- In the case of MW-hr, the M is an abbreviation for 106 ... whereas in the case of MMBtu and MMkcal, M is an abbreviation for 103. This is an unfortunate irregularity, but one which is actually in use.
Conversion Factors and Dimensional Analysis:
Every physical measurement consists of a numerical quantity and a corresponding dimensional unit (for example: 1000 kg / m3, 50 miles / hour, 1000 Btu / lb, etc). Whenever it is necessary to convert a physical measurement from one dimensional unit to another, dimensional analysis (also known as the unit-factor method or the factor-label method) is quite useful.
But what is dimensional analysis in the context of converting dimensional units? It is the sequential usage of various conversion factors expressed as fractions and arranged so that any dimensional unit appearing in both the numerator and denominator of any of the fractions can be cancelled out until only the desired set of dimensional units is obtained. For example, let us convert 10 miles per hour to meters per second:
10
———— —————— ——————— = ——————
1
As can be seen, when the mile dimensions and the hour dimensions are cancelled out and the arithmetic is done, we have converted 10 miles per hour to 4.47 meters per second.
As another example, convert the ppmv of NOx in an exhaust gas (denoted as C) to grams per hour of NOx, given the molecular weight of NOx as 46.01, and the rate of exhaust in scf per minute (denoted as E):
C,
———————– ——————— ————— ————– —————— ————— = ——––
106
As shown in the above equation, after cancelling out any dimensional units that appear both above and below the division lines, the only remaining units are grams / hour. Thus:
grams / hour of NOx = (C, ppmv of NOx) (E, scf of exhaust / minute) / 303.05
Note: A standard cubic foot (scf) is the USA expression of gas volume at 60 °F and 1 atmosphere of pressure and, using that definition, there are 379.48 scf per pound-mole of any gas. There are other definitions of standard gas conditions used in the USA besides 60 °F and 1 atmosphere, but this is the most common one.
The same example, using metric units:
C,
———————— ———————– ————— —————— —————— = ——––
106
As shown in the above equation, after cancelling out any dimensional units that appear both above and below the division lines, the only remaining units are grams / hour. Thus:
grams / hour of NOx = (C, ppmv of NOx) (E, Nm3 of exhaust / minute) / 8.12
Note: A normal cubic meter (Nm3) is the usual metric system expression of gas volume at 0 °C and 1 atmosphere of pressure and, using that definition, there are 0.02214 Nm3 per gram-mole of any gas.
Dimensional analysis can also be used to check the correctness of any mathematical equation involving dimensional units by checking to see that the dimensional units on the left hand side of the equation are the same as the dimensional units on the right hand side of the equation.
Appendix A: Concentration Units: ( ppm and mg/m3 )
(1) The term ppm is an acronym for parts per million. In the context of airborne gaseous pollutant concentrations, it stands for volumes of gaseous pollutant X per million volumes of air. As discussed further below, it is very important to use the terms ppmv or ppm by volume rather than simply ppm.
Some airborne gaseous pollutant concentrations may be expressed as ppbv or ppb by volume, meaning volumes of gaseous pollutant per billion volumes of air.
(2) For an airborne gaseous or non-gaseous pollutant concentration, the term mg/m3 stands for milligrams of substance X per cubic meter of air.
Some airborne gaseous or non-gaseous pollutant concentrations may be expressed as ug/m3, which stands for microgams of substance X per cubic meter of air.
(3) The hazardous concentration limits set by NIOSH, OSHA and ACGIH are for the most part directed at airborne pollutants (i.e., gases, vapors, dusts, aerosols, and mists). Hazardous substances dissolved in water or any other liquid are generally not within the purview of NIOSH, OSHA and ACGIH.
(4) Airborne pollutant concentration limits are usually expressed as parts per million by volume (i.e., ppmv) for gases and vapors, and mg/m3 for dusts, aerosols and mists.
(5) Quite often you will find the hazardous concentration limit of an airborne gaseous pollutant expressed as either ppmv or mg/m3 or both. There is a simple mathematical method of converting one to the other for gaseous substances (as given earlier in this article). However, for non-gaseous pollutants such as dusts, mists or aerosols, it would be very difficult, if not impossible, to convert mg/m3 to ppmv.
(6) When dealing with hazardous substances dissolved in water or any other liquid, most chemists would use the term parts per million by weight (i.e., ppmw) as meaning weight of dissolved substance X per million weights of liquid ... where the weight units might be in milligrams (mg) or grams (g) or pounds (lb) or kilograms (kg).
In a few cases, chemists might use ppmv as meaning volumes of gas or liquid dissolved in water or other liquid per million volumes of water or other liquid. For example, gaseous carbon dioxide dissolved in water ... or liquid acetone dissolved in water ... or liquid additive dissolved in gasoline.
(7) The numerical difference between a concentration expressed as ppmv or ppmw can be very large, especially for gaseous substances. Thus, it is most important to be as specific as possible and to use the terms ppmv or ppmw rather than simply ppm. Confusion as to whether ppm means ppmv or ppmw can have serious consequences. It is also important to state whether you are dealing with substances in the air or substances within water or other liquid.
(8) Finally, keep in mind that if something can be mis-construed, it will happen. Be as specific as possible in defining concentration limits. If you find an exception to what is said above, it is either valid because of some special or unusual reason, or the exception is simply incorrect.
Some Technical Concepts and
Terms Explained
|
Compound*
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Explanation
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benzo[a]pyrene, is the best
known and most-measured PAH
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Carbon Monoxide
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Carbon Dioxide
|
|
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Oxides of Nitrogen
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|
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Policyclic aromatic
hydrocarbons
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Peroxyacetyl nitrate
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Polyvinyl Chloride
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Particulate Matter of 10
microns or less
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|
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Suspended Particulate Matter
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|
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Sulfur Dioxide
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|
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Total Suspended Particles
|
|
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Volatile Organic Compounds
|
|
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Non- Methane Volatile Organic
Compounds
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Units
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|
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m
|
metres
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g
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gram
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mg
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milligrams (10-3 grams)
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µg
|
microgram (10-6 grams)
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ppm
|
parts per million
(volume/volume)
|
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ppb
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parts per billion (volume/volume)
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mg/m3
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milligrams per cubic metres
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µg/m3
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micrograms per cubic meter
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* For descriptions of
pollutants,
|
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25oC,1 atm
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Sulfur dioxide
SO2
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1 ppm = 2,860µg/m3
1mg/m3 = 0.35 ppm
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Carbon Monoxide
CO
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1 ppm = 1.145mg/m3
1mg/m3 = 0.873 ppm
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Nitric Oxide
NO
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1ppm = 1,230 µg/m3
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Nitrogen Dioxide
NO2
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1 ppm = 1,880µg/m3
1 µg/m3 = 0.000532 ppm
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Benzene
C6H6
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1 ppm = 3.19mg/m3
1mg/m3 = 0.313 ppm
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Hydrogen Sulfide
H2S
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1ppm = 1.5mg/m3
1mg/m3 = 0.670 ppm
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Vinyl Chloride
VC
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1ppm = 2.589mg/m3
1 mg/m3 = 0.386 ppm
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Toluene
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1ppm = 3.75 mg/m3
1 mg/m3 = 0.226 ppm
|
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Trichloroethylene (TCE)
C2HCl3
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1ppm = 5.4mg/m3
1mg/m3 = 0.18 ppm
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Tetrachloroethylene
C2Cl4
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1ppm = 6.78mg/m3
1 mg/m3 = 0.14 ppm
|
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Styrene
C6H5.CH=CH2
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1 ppm = 4.2mg/m3
1mg/m3 = 0.24 ppm
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Formaldehyde
HCHO
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1 ppm = 1.2mg/m3
1mg/m3 = 0.833ppm
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Peroxyacetyl nitrate
PAN
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1 ppm = 5mg/m3
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Carbon Disulfide
CS2
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1 ppm = 3.13mg/m3
1mg/m3 = 0.32 ppm
|
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Ethylene dichloride
(1,2-Dichloroethane, DCE)
C2H4Cl2
|
1ppm =4.12mg/m3 (at 20oC)
1mg/m3 = 0.242 ppm
|
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Dichloromethane
CH2Cl2
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1 ppm = 3.47mg/m3
1 mg/m3 = 0.28 ppm
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Ozone
O3
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1 ppm = 2mg/m3
|
*For conversions between ppm,
ppb, mg/m3 and ug/m3: MolWeight x PPM = 24.45 x mg/m3 or MolWeight
x PPB = 24.45 x ug/m3
Acute Health Effects:
Those immediate health effects
resulting from exposure to an episode of air pollution e.g. asthma attack. In
certain conditions, acute episodes of air pollution are also associated with an
overall increase in respiratory and cardiovascular mortality.
Adverse Effect:
Any effect that may affect the
performance of the whole organism or that reduces an organism's ability to
respond to an additional pollutant.
Background Concentration:
The normal concentration of a
particular air pollutant occures naturally in the environment (also without any
human activity). This is determined by the natural characteristics of an area
like the presence of deserts, volcanoes, etc.
Carcinogenic:
A substance that causes
abnormal, uncontrolled growth of cells or cancer, like lung cancer or
leukaemia. This includes benzene, benzo-a pyrene (BaP) and heavy metals like
lead, arsenic, nickel, cadmium etc.
Carcinogenic and Toxic Health
Effects:
Those health effects resulting
from exposure to carcinogenic (cancer causing) substances.
Cardiovascular Disease:
Heart related disease
Chronic Health Effects:
Those health effects owing to
long term exposure to lower levels of pollution e.g. bronchitis resulting from
SO2 exposure, or the increased respiratory and cardiovascular mortality
observed in a number of epidemiological studies due to exposure to particulate
matter. (ENDS, 1994)
Cost Benefit Analysis (CBA):
An analysis of the costs of
pollution abatement versus the benefits to be derived from such abatement
measure: both of which are expressed in monetary terms.
Cost Effective Analysis (CEA):
An analysis of the costs of
abatement measures whose benefits are expressed in physical terms such as
reduced emissions or reduced concentrations.
Dispersion Model:
A dispersion model is a software
programme that assesses/calculates the concentrations of a specific pollutant
on the basis of the emissions of the polluting activity sectors, at a certain
point in time and space. These models account for geographic factors such as
wind speed, temperature and direction. e.g. CAR International, IMMIS LUFT, BLB
etc., Dispersion models help to limit the complex and often expensive ambient
air monitoring since it calculates the ambient air quality in a given area and
identifies where the emissions are likely to have an impact. However, regular
monitoring will remain important to validate the models and determine the
natural background concentration.
Emission:
Any measurable air contaminant,
pollutant, gas stream, or unwanted sound from a known source which is passed
into the atmosphere
Emission Control Device:
Any device that is placed in a
system to reduce the amount of air pollutants released into the environment.
Emission Factor:
This is a constant which relates
the emission of a certain compound to the input or output of another compound
by the same source, e.g. the emissions of SO2 by a factory can be estimated
from its coal consumption. Emission factors are useful in cases where emissions
data are missing. They can be used to make a rough estimate of emissions, based
on economic activities, traffic and number of households, followed by the use
of dispersion models to assess concentrations.
(OR: a numerical estimate of the
mass of one or more air contaminant produced by a given amount of material
processed by an industrial facility or, in the case of transportation sources,
per mile driven (by a given vehicle using a particular fuel). It is important
to note if the emission factor is for an uncontrolled source or one with
properly functioning air pollution control equipment. This factor is used to
arrive at a rough estimate of the total air emissions for a facility or a
geographical area.)
Emission Inventory:
A compilation of estimated air
emissions by pollutant from smokestacks, cars and other emission sources in a
given area.
Emission Standards:
Legal limits on the degree or
quantities of pollutants that are permitted to be discharged to the atmosphere
from specific sources or process, e.g. emissions from vehicles or from
industrial sources.
Environmental Impact Assessment
(EIA):
The process of analyzing the
probable environmental effects, both positive and negative, of a proposed
project, programme or policy and suggesting ways to mitigate the adverse
effects, including the identification of alternatives or other ways of
implementing parts of it.
Episode:
A series of short-term air
pollution events that significantly alter the ambient air quality of an
affected area.
Lowest Achievable Emission Rate:
Any technology or combination of
technologies and process controls that result in the lowest possible emission
of a given air pollutant. The technology must be reasonably demonstrated to be
appropriate and reliable for the given application.
Lowest Observed Adverse-Effect
Level (LOAEL):
The lowest experimental dose of
a chemical at which there is statistically or biologically significant increase
in the severity or frequency of a toxicity effect.
Mobile Sources:
Those sources of pollution that
emit pollutants along their path of movement e.g. road transport and off road
mobile sources.
Mutagen:
A substance that causes mutation
or the alteration of the basic genetic structure of any living organism
No Observed Adverse Effect Level
(NOAEL):
The highest experimental dose of
a chemical at which there is no statistically or biologically significant
increase in the frequency or severity of a toxicity effect between an exposed
group and its appropriate control.
Respiratory Effects:
Air pollution problems related
to the respiratory/ breathing difficulties, sometimes resulting in acute
effects like asthma and fatal heart attacks.
Stationary Sources:
Those sources of air pollution
that emit the pollutants from a fixed-point e.g. industrial plants, power
generation facilities, domestic cooking and heating, agricultural activities
etc.
Threshold:
The point below which the
environment is not harmed by any pollutant.
Threshold Value:
Denotes the concentration of a
pollutant below which no negative effects are expected.
Threshold Level:
The minimum dose of a toxic substance
that causes harmful effects in any ecosystem.
Threshold Limit Value (TLV):
The concentration of an airborne
contaminant to which workers may be exposed regularly without adverse effect.
The TLV recognizes that there are some individual variations among workers and
that maintaining exposures within the limits may not prevent discomfort or
aggravation of a pre-existing condition in some individuals. Most TLVs
represent average exposures and some fluctuations during the day is possible
without causing adverse effects.
Wavelength:
The distance separating one wave
crest from the next in any uniform succession of traveling waves.
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