Ap-221: using pids to assess exposure risk in unknown environments

Using PIDs To Assess Exposure Risk In Unknown Environments
Risk Decisions Based on PIDs
Correction Factors are the Key
Photoionization detectors (PIDs) can measure volatile Correction Factors are the key to unlocking the organic compounds (VOCs) and other toxic gases at power of a PID for assessing varying mixtures and concentrations from parts per billion (ppb) to 10,000 unknown environments. They are a measure of PID parts per million (ppm). This sensitivity allows PIDs sensitivity to a particular gas. CFs permit calibration to be used to make accurate, instantaneous decisions on one gas while directly reading the concentration of as to the levels of ionizable chemicals to which another, eliminating the need for multiple calibration workers are exposed. By simultaneously solving for gases. PID manufacturers determine Correction human and PID meter sensitivity, a logical program Factors by measuring a PID’s response to a known of atmospheric risk reduction based upon PID concentration of target gas. Correction Factors are response can be implemented in both known and instrument and/or manufacturer specific, so it is important to use the CFs from the manufacturer of the PID. Therefore, it may be best to choose a PID Two Sensitivities Must Be Understood
manufacturer with the largest listing of CFs. PID In order to make an assessment of toxicity risk with a manufacturers publish CF lists and some integrate PID, two sensitivities must be understood: this information into the microprocessor of the PID. Microprocessor PIDs, like the MiniRAE 2000, can 1. The first is human sensitivity and is expressed automatically store and apply over 100 CFs. in exposure limits defined by organizations such as OSHA (the US Occupational Safety Three Scenarios on How to Set PID Alarms:
and Health Administration), NIOSH (the US In order to better understand making a decision that National Institute for Occupational Safety and combines these two sensitivities we can look at three specific examples of applying a PID to make an Governmental Industrial Hygienists) or other typically expressed in parts per million (ppm) 2. Gas/vapor mixture with constant make-up 2. The second sensitivity is that of the PID. This 3. Gas/vapor mixture with varying make-up sensitivity factor is called a Correction Factor (CF) or sometimes a Response Factor. The CF 1. PID Alarms for a Single Gas/Vapor
is a ratio of the PID sensitivity to a particular It is comparatively easy to gain information on a chemical referenced to the PID calibration gas of isobutylene. CFs are specific to a PID brand (for more information on CFs and how PIDs work, refer to RAE Systems’ AP-000: PID • Set the PID correction factor to that chemical from the PID manufacturer’s listing. This solves • Find the Exposure limit(s) for the chemical (refer PID sensitivity + Human Sensitivity = Decision • Set the PID alarms according to the exposure Most PIDs can automatically do the math involving CF, so, for example, all the user has to do is select RAE Systems Inc.
3775 N. First St., San Jose, CA 95134-1708 USA Phone: +1.888.723.8823 Email: [email protected] Web Site: www.raesystems.com “toluene” from the PID library, and the PID is In a similar manner the Correction Factor is measuring in “toluene” ppm. Then set the PID alarm to the appropriate value (100 ppm for OSHA), and the PID is able to accurately make “toluene” • 0.4 is the CF for styrene • 0.85 is 85% xylene 2. PID Alarms for a Gas/Vapor Mixture with
Constant Make-up
Often processes do not involve a single chemical, but may involve a compound that is a mixture of toxic The reading in the area with the paint odors was 120 chemicals. This “witches’ brew” of toxic compounds on the PID in isobutylene units. Multiplying this requires greater care in determining alarm setpoints. reading by the correction factor of 0.56, an actual If the contents of the mixture are identifiable, the concentration in mixture units was 67.2 ppm. This is individual chemicals and their concentrations should under the calculated exposure limit of 87 ppm of be easily determined through a contents label or mixture. If the reading were 178 ppm in isobutylene MSDS. Then the following equation can be used to units, the actual concentration would be 100 ppm of the mixture, consisting of 15 ppm styrene and 85 ppm xylene. This mixture reading is over the exposure limit of 87, even though none of the components are over their individual exposure limits. “EL” is the Exposure Limit and X is the mole fraction (percent by volume) of each volatile Note: An Excel format spreadsheet is available at the
chemical. Similarly, the Correction factor for the end of the online version of Technical Note TN-106 mixture can be calculated using the following at www.raesystems.com. It allows calculations of CFs and alarm limits for complex mixtures. 3. Setting PID Alarms for a Gas/Vapor
Mixture with Varying Make-up:
To clarify the usage of these equations lets take an The “Controlling Compound”
example. Suppose that you have a complaint of paint Many times we can identify the chemicals odors and upon investigating you find that the paint present, but their relative concentrations vary contains 15% styrene and 85% xylene. Then the exposure limit is calculated as follows: throughout a process. Or, in situations like HazMat Response, one cannot predict the ELmix = 1/(0.15/50 + 0.85/100) = 87 ppmmix concentrations. Therefore, we have to look at another way of using the PID to make decisions. Setting alarms in a varying or unknown mixture • 50 is the 50 ppm exposure limit for styrene means that you have to simultaneously interpret both the human sensitivity (exposure limits) and • 100 is the 100 ppm exposure limit for xylene PID sensitivity (Correction Factors) for all of the RAE Systems Inc.
3775 N. First St., San Jose, CA 95134-1708 USA Phone: +1.888.723.8823 Email: [email protected] Web Site: www.raesystems.com chemicals involved. Fortunately, this is easier than it sounds. Every mixture has a compound that is the most toxic and “controls” the setpoint for the whole mixture. Determine that chemical, So to get the exposure limit in units of isobutylene and you can determine a conservative setpoint we divide the exposure limit in chemical units by the for the entire mixture. The basic assumption is ratio of chemical units to isobutylene units. that if we are safe for the “worst” chemical in a mixture, we will be safe for all of the others. Chemical
10.6eV ELChemic ELIsobutyl
1. Express all exposure limits in equivalent 2. Look for the compound with the lowest 3. Set the PID for that setpoint, and you are safe for all of the chemicals in the mixture. In Table 2, the far right column expresses all of the exposure limits in equivalent units of isobutylene. Now the chemicals can be compared on equal footing. One can compare apples to apples. While Chemical
Exposure
humans are not as sensitive to ethanol as they are to toluene, the low PID sensitivity to ethanol combined with the highest exposure limit in the table makes ethanol the “controlling compound” when the exposure limits are expressed in equivalent isobutylene units. In this example, the PID is left on Table 1 is a simple example where ethanol appears to an isobutylene measurement scale and the alarm is be the safest compound and toluene appears to be the set to 83 ppm. As long as the PID does not alarm, most toxic. This is because most people are then no respiratory protection is required. accustomed to making decisions solely on human sensitivity. Users of meters rarely take into account Important: In the rest of this discussion, exposure
that, like humans, meters have varying sensitivities to limits in “Isobutylene Units” calculated by different chemicals. Therefore, Table 1 only provides half of the decision-making equation. The exposure limit is expressed in units of different chemicals. When trying to use a PID to make a decision regarding which is the “worst” chemical, one might be comparing 1000 apples to 100 will be called RAE Units (RU) because their pineapples. What is required is to express the calculation involves a RAE Systems PID Correction exposure limits in a common unit of measurement. Factor which should only be applied to RAE Systems Because PIDs are calibrated to isobutylene, and PIDs. Similar calculations can be done for any other Correction Factors are expressions of PID sensitivity PID brand that has a published list of correction to a chemical relative to isobutylene this is very easy to do. First let’s look at this theoretically: Note: Setting alarm limits this way is the most
conservative, restrictive approach, required by Chemical: Exposure Limit in chemical units (ppm). the limited information. When compound ratios Unless otherwise indicated the EL is typically an 8- are known better, the methods in Section 2 always allow higher alarm settings and fewer CF = PID Isobutylene Response x Concentration of gas (ppmv) Conc. of isobutylene (ppmv) x Response of gas on PID RAE Systems Inc.
3775 N. First St., San Jose, CA 95134-1708 USA Phone: +1.888.723.8823 Email: [email protected] Web Site: www.raesystems.com
Utilizing RAE Unit Logic to help Characterize
Of the 270 compounds that are or may be ionizable, Unknown Environments
RAE Systems currently has Correction Factors (CF) RAE Units provide people who need to characterize for 121 compounds using the 10.6eV lamp (the most unknown environments (HazMat technicians, health common PID lamp). These 121 compounds account and safety professionals, indoor air quality for 45% of the potentially ionizable compounds on consultants) with an important tool. It allows them to gauge the risk to themselves and others. The higher The 50/50 Rule
the chemical’s RU, the less risk. If the RU (isobutylene equivalent) is below the threshold for a Using the RAE Unit logic allows one to use the PID particular chemical, it does not pose a threat. For to help determine standard operating procedures example, if the PID reads 45 ppm isobutylene in an (SOPs) because one can know exactly what area with toluene (RU=400), styrene (RU=250) and chemicals the PID will provide protection from, cumene (RU=92) vapors, we are safe because the RU given a particular reading in isobutylene units. Table for all three of these chemicals is well above 45 ppm 3 is a list of 174 chemicals combining OSHA-Z, NIOSH, AGCIH and other exposure limits. Because they are enforceable by law, OSHA exposure limit, Acceptable levels of exposure can change with the take precedence in Table 3 when there is a difference circumstances. In a “normal” HazMat response (like in exposure limits between OSHA, NIOSH and a truck rollover), a 50 ppm RU alarm might be the AGCIH. A RAE Systems PID with a 10.6eV lamp most appropriate for going to respiratory protection (the most common PID lamp) set to the following because the typical threat is hydrocarbons from fuel alarms and not beeping provides protection from: products and a RU alarm of 50 is very conservative
•
for all hydrocarbon fuels. However, in a potential 44 chemicals at a 100 ppm alarm, includes
terrorist chemical agent attack, a RU of 1.00 ppm major solvents like xylene, toluene, MEK, MPK, might be more appropriate because it is below the LCT50 (Lethal Concentration) for mustard (LCt50 65 chemicals at a 50 ppm alarm, from sec-amyl
RU=385), Sarin (LCt50 RU=2.61) and Tabun (LCt50 RU=25). RAE Units are only one guage of the threat • 81 chemicals at a 25 ppm alarm, from
level in any circumstance. The PID user must use all of the clues present to reach a decision. In the • 105 chemicals at a 10 ppm alarm, from
preceding example, we would also look to see if victims were affected. If not, we might have a hoax • 140 chemicals at a 1 ppm alarm, from
on our hands. If victims were showing the telltale diethylenetriamine to acetone. (Note: A
signs of chemical exposure, more monitoring assets ppbRAE is highly recommended when using the would be required to make a determination as to the type of chemical agent (Reference AP-216: Using Of course, setting an alarm to 1 ppm would provide the highest level of protection, but it would also RAE Units and OSHA’s Z-Listed Chemicals
provide the most alarms. Too many alarms would be There are approximately 436 chemical compounds on like “the boy who cried wolf” and would reduce user OSHA’s Z-List. The approximate breakdown is as confidence in the PID. An alarm point of 1 ppm would be similar to always wearing a Level A suit! The RAE Systems MultiRAE Plus and ToxiRAE PIDs are factory set with a low alarm at 50 ppm on an isobutylene scale. This alarm point provides • Non-ionizable vapors with Ionization protection from some of the most common chemicals in industry and is a good balance point between too many and too few alarms. One way of looking at this is with 50 ppm alarm in isobutylene units and the PID is not beeping, users don’t have to worry about RAE Systems Inc.
3775 N. First St., San Jose, CA 95134-1708 USA Phone: +1.888.723.8823 Email: [email protected] Web Site: www.raesystems.com more than 50 (65, exactly) common chemicals. Ethyl silicate
100.000
140.85
Hence, this is known as the RAE Systems “50/50 Hexone (Methyl isobutyl
0.80 100.000
125.00
ketone)
Pentane 8.40
1000.000
119.05
Table 3: RAE Unit Alarms Points for a
Tetrahydrofuran 1.70
200.000
117.65
10.6eV Lamp
Chemical Name
Hexane, n-
4.30
500.000
116.28
Note: OSHA Z-Listed Chemicals are in bold Italics
Dichlorobenzene (o-)
0.47
50.000
106.38
Chemical Name
Butyl acetate, (tert-)
2.00
200.000
100.00
Acetone 1.10
1000.000
909.09
Petroleum distillates
500.000
704.23
Stoddard Solvent
0.71
500.000
704.23
100 ppm Alarm
Isopropyl ether
0.80
500.000
625.00
Isopropyl acetate
2.60
250.000
96.15
Methylcyclohexane 0.97
500.000
515.46
Cumene 0.54
50.000
92.59
Trichloroethylene 0.54
50.000
92.59
Toluene 0.50
200.000
400.00
Dioxane, 1,4-
1.10
100.000
90.91
Ethyl acetate
4.60
400.000
86.96
Cyclohexene 0.80
300.000
375.00
Diethyl ether
1.10
400.000
363.64
Ethyl alcohol
12.00
1000.000
83.33
Diacetone alcohol
0.70
50.000
71.43
Turpentine 0.35
100.000
285.71
Octane, n-
1.80
500.000
277.78
Styrene 0.40
100.000
250.00
Isopropyl Alcohol
6.00
400.000
66.67
Methyl ethyl ketone
0.86
200.000
232.56
Methyl methacrylate
1.50
100.000
66.67
Xylene, m-
0.43
100.000
232.56
Butyl acetate, (n-)
2.60
150.000
57.69
Xylene, p-
0.45
100.000
222.22
Isobutyl acetate
2.60
150.000
57.69
Pentanone(2-) (Methyl
0.93 200.000
215.05
Propyl acetate, n-
3.50
200.000
57.14
propyl ketone)
Cyclohexanone 0.90
50.000
55.56
Cyclohexane 1.40
300.000
214.29
Amyl acetate (sec-)
2.30
125.000
54.35
Xylenes (o-, m-, p-
100.000
204.08
isomers).
50 ppm Alarm
Methyl styrene(alpha-)
0.50
100.000
200.00
Isoamyl acetate
2.10
100.000
47.62
Ethyl benzene
0.52
100.000
192.31
Chlorobenzene 0.40
75.000
187.50
Perchloroethene 0.57
25.000
43.86
Heptane, n-
2.80
500.000
178.57
Amyl acetate (n-)
2.30
100.000
43.48
Xylene, o-
0.59
100.000
169.49
Butoxyethanol, 2-
1.20
50.000
41.67
Ethoxyethanol (2-),
1.30 200.000
153.85
Butyl alcohol (sec-)
4.00
150.000
37.50
(Cellosolve)
Naphtha (Coal tar)
2.80 100.000
35.71
Chemical Name
Butyl alcohol (tert-)
2.90
100.000
34.48
Acetaldehyde 6.00
200.000
33.33
RAE Systems Inc.
3775 N. First St., San Jose, CA 95134-1708 USA Phone: +1.888.723.8823 Email: [email protected] Web Site: www.raesystems.com
Propyl alcohol (n-)
6.00
200.000
33.33
Methyl acetate
6.60
200.000
30.30
Phenol 1.00
5.000
5.00
Triethylamine 0.90
25.000
27.78
Nitric oxide
5.20
25.000
4.81
Isobutyl alcohol
3.80
100.000
26.32
Butylamine, n-
5.000
4.55
Diethylamine 0.97
25.000
25.77
Chemical Name
Hydrogen sulfide
3.30
10.000
3.03
25 ppm Alarm
Chemical Name
Naphthalene 0.42
10.000
23.81
Methyl acrylate
3.70
10.000
2.70
Methyl iodide
0.22
5.000
22.73
Butyl alcohol (n-)
4.70
100.000
21.28
Chemical Name
Benzene 0.53
1.000
1.89
Naphtha (Coal tar)
5.70 100.000
17.54
Crotonaldehyde 1.10
2.000
1.82
Butyl mercaptan
0.60
10.000
16.67
Benzyl chloride
0.60
1.000
1.67
Carbon disulfide
1.20
20.000
16.67
Propylene imine
1.25
2.000
1.60
Ethyl mercaptan
0.60
10.000
16.67
Methyl mercaptan
0.60
10.000
16.67
Phenyl ether, vapor
0.70
1.000
1.43
Propylene oxide
6.50
100.000
15.38
Dimethyl acetamide, N,N-
0.80
10.000
12.50
Dimethylformamide, N,N-
0.80
10.000
12.50
Butadiene 0.85
1.000
1.18
Ethylamine 0.80
10.000
12.50
Iodine 0.10
0.100
1.00
Dibromoethane, 1,2-
1.70
20.000
11.76
1 PPM Alarm
Methyl bromide
1.70
20.000
11.76
Allyl alcohol
2.40
2.000
0.83
Aniline 0.48
5.000
10.42
Acetic Anahydride
6.10
5.000
0.82
Ethanolamine (Not
4.00 3.000
0.75
Ethyl acrylate
2.40
25.000
Recommended)
Methoxyethanol, 2-
2.40
25.000
Dimethylhydrazine, 1,1-
0.78
0.500
0.64
Toluidine, o-
0.50
5.000
10 PPM Alarm
Chloroprene (beta-)
3.00
25.000
Epichlorohydrin 8.50
5.000
0.59
Methylamine 1.20
10.000
8.33
Nitrobenzene 1.90
1.000
0.53
Vinyl chloride
2.00
1.000
0.50
Acetic Acid
22.00
10.000
0.45
Pyridine 0.68
5.000
7.35
Diisopropylamine 0.74
5.000
6.76
Allyl glycidyl ether
1.50
10.000
6.67
Hydrazine 3.00
1.000
0.33
Dimethylamine 1.50
10.000
6.67
Nitrogen dioxide
16.00
5.000
0.31
Diphenyl (Biphenyl)
0.70
0.200
0.29
Furfural 0.92
5.000
5.43
Ammonia 9.70
50.000
5.15
Allyl chloride
4.30
1.000
0.23
Dichloroethyl ether
15.000
5.00
Bromoform 2.50
0.500
0.20
RAE Systems Inc.
3775 N. First St., San Jose, CA 95134-1708 USA Phone: +1.888.723.8823 Email: [email protected] Web Site: www.raesystems.com
Methyl hydrazine
0.200
0.17
(Monomethyl hydrazine)
Phosphorus trichloride
0.500
0.13
Nicotine 0.70
0.075
0.11
Bromine
Ethylene oxide
13.00
1.000
0.08
Phosphine 3.90
0.300
0.08
RAE Systems Inc.
3775 N. First St., San Jose, CA 95134-1708 USA Phone: +1.888.723.8823 Email: [email protected] Web Site: www.raesystems.com
Chemical Name
References
Below Normal Outside
ACGIH, 2000 TLVs and BEIs, ACGIH, Cincinnati,
Air Background Values
of 0.05 ppm (50 ppb)
Maslansky/Maslansky; Air Monitoring
Dimethyl sulfate
20.00
1.000
0.05
Instrumentation, Van Nostrand Reinhold, New
Tetraethyl lead (as Pb)
0.30
0.008
0.03
NIOSH: Pocket Guide to Chemical Hazards,
Acrolein 3.90
0.100
0.03
Toluene-2, 4-diisocyanate
0.020
0.01
OSHA: 1910.1000 TABLES Z-1
(TDI)
RAE Systems: Correction Factors, Ionization
Potentials, and Calibration Characteristics
(Technical Note TN-106)
Wrenn, Christopher A.; AP-211: PIDs for
Continuous Monitoring of VOCs, RAE System,
San Jose, CA.
Wrenn, Christopher A.: PID Training Outline,
RAE Systems, San Jose, CA
RAE Systems Inc.
3775 N. First St., San Jose, CA 95134-1708 USA Phone: +1.888.723.8823 Email: [email protected] Web Site: www.raesystems.com

Source: http://www.ecoenvironmental.com.au/eco/downloads/gas_MiniRAE_2000_Assessment_of_Exposure_Risk_in_Unknown_Environments.pdf