Technically Speaking by Dr. John Nordin

Figuring Out Information on Chemicals Can Be Frustrating

We have all run into the problem of researching information on chemicals. Do we have the right chemical? Is Phenylenediamine the same as n-Phenylenediamine? Is Isopropyl methylphosphoniofluoridate another name for Sarin? Is Mercury chloride the same as mercuric chloride? What is the difference between 5 ppm chlorine and 5 mg/m³ chlorine? If an organic chemical has a vapor pressure of 30 torr, what does this mean? What is a KPa? What is the difference between open cup and closed cup flash points? Why do some chemicals boil over a range of temperatures and some have a unique boiling temperature? Why do reference sources sometimes disagree? 

Different Chemical Names

In the previous example we looked up information for methanol. The information was displayed under methyl alcohol. Methanol is a synonym for methyl alcohol. It is a fact of life that the same chemical can go by different names. Some chemicals can go by as many as 30 or 40 different synonyms, not to mention different names for chemicals in different languages.

Why so many names? One reason is chemists have a code for naming complex chemicals. These names may be very long in the case of complex organic chemicals, so short names of only a few letters are invented because they are easy to remember. There are also different codes or methods of naming chemicals resulting in different names. The International Union of Pure and Applied Chemistry (IUPAC) has established rules for naming complex chemicals by chemists [visit the website for rules on naming organic chemicals].

A chemist using a proper code name for the particular chemical can give it to another chemist, and that chemist will know the chemical structure. The PEAC tool contains both chemical code names and common names for the chemical. For example, a certain pesticide has a chemical name 1-[2-Chlorophenylsulfonyl]-3-[methoxy-6-methyl-1,3,5-triazin-2-yl]urea, but the pesticide is more commonly known by the names chlorsulfuron or chlorosulfuron [chlorsulfuron is the name registered with the EPA]. If one selects the long-handled chemical name, 1-[2-chlorophenyl into the PEAC tool, it is linked up to the more common name for the chemical. The long-handled name has meaning to chemists, but first responders may choose to use the shorter, common name. This same chemical is known by another long chemical name, 1-chloro-N-[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]benzenesulfonamide.

There may be situations where the long chemist name is used but not the common name. If this is not bad enough, there may be variations in how the chemical is spelled or how the number and component parts are ordered, for example, chlorosulfuron or chlorsulfuron is also known by 2-chloro-N-[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)aminocarbonyl)benzenesulfonamide. Sometimes the chemical is known by brand names (short names used by the manufactuer). Examples of brand names are Glear, Telar, and Trilixon. Teilixon is a powder containing chlorsulfuron and methabenzthiazuron as active ingredients. 

Why not use only common names which are more easily remembered? A particular chemical may have many common names, and the names are also different in different languages. Generally, the long chemical name is the same in any language but there are some exceptions to this.

The American Chemical Society has assigned a unique number for each chemical called the Chemical Abstract Service or CAS number. The original intent of the number was to aid scientists and other researchers to locate information about the chemical in the literature, a sort of catalog system for chemicals. The CAS number for Chlorsulfon is 64902-72-3. This number can be typed in many computerized data bases including the PEAC tool to pull up information about the chemical. It also appears on many labels listing product ingredients supplied with chemicals. The CAS number is internationally recognized. When in doubt whether the name matches a data base, get a match for the CAS number. 

Different Units of Measurement

The PEAC tool user has the option of selecting English or metric (international) units for display. To select this option, the user clicks on edit at the top of the screen, then options. A screen pops up like the one below over other screens. The user can select English or metric.

When getting information from different data sources, the data may be expressed in different units. A good conversion table and pocket calculator are necessary. 

Table 1. Conversion Table

Measurement Type	To Convert From:	To Convert To:	Do This
Temperature	o F	o C	Subtract 32 from oF and multiply result by 5/9
Temperature	o C	o F	Multiply by 9/5 and add 32
Concentration	ppm	mg/m3	Multiply ppm by the molecular weight and divide the result by 24.45
Concentration	mg/m3	ppm	Multiply mg/m3 by 24.45 and devide the result by the molecular weight
Concentration	Volume %	ppm	Multiply by 10000
Pressure	mm Hg	atm	Divide by 760
Pressure	atm	mm Hg	Multiply by 760
Pressure	psi	atm	Multiply by 0.06805
Pressure	atm	Inches Hg	Multiply by 29.921
Pressure	atm	KPa (kilopascals)	Multiply by 101.325
Pressure	atm	psi	Multiply by 14.696
Pressure	Torr	mm Hg	Multiply by 1
Pressure	Torr	KPa	Multiply by 0.13332
vap. pressure	atm	Vap by volume	Multiply by 100
Weight/mass	Pounds	grains	Multiply by 7000
Weight/mass	Pounds	kilograms	Multiply by 0.45359
Weight/mass	kilograms	Pounds	Multiply by 2.2046
Volume	Gallons	Cubic Feet	Multiply by 0.13368
Volume	Gallons	Liters	Multiply by 3.785
Volume	Gallons	Cubic meters	Multiply by 0.003785
Volume	Barrels (oil)	gallons	Multiply by 42
Power	Horsepower (British)	Horespower (metric)	Multiply by 1.0139
Power	Watts	B.T.U./hr	Multiply by 3.413
Power	Watts	Joules/second	Multiply by 1
Work	Joules	B.T.U.	Multiply by 0.000948
Work	Joules	Calories	Multiply by 0.2389
Work	Joules	Kilowatt-hours	Multiply by 0.00000027778
Work	Kilocalories	Joules	Multiply by 4186.8
Length	Feet	Meters	Multiply by 0.3048
Length	Miles	Meters	Multiply by 1609.3
Length	Miles	km	Multiply by 1.6093
Radiation Activity	Becquerel (Bq)	Disintegrations/second	Multiply by 1
Radiation Activity	Becquerel (Bq)	Curies	Multiply by 2.703 x 10-11
Radiation dose	Roentgen	rem	Dose absorbed is equivalent for gamma and x radiation, different factors apply for neutron and other radiation
Radiation dose	rem	Sievert	Multiply by 0.01

Example: The concentration of sulfur dioxide is 5 ppm. What is the concentration in mg/m³?

Answer: The molecular weight of sulfur dioxide is 64.1. The concentration in mg/m³ (milligrams per cubic meter) is 5 x 64.1/24.45 = 13.11 mg/m³ (call it 13 mg/m³ , the numbers are usually rounded).

Someone might ask: Wouldnt the answer be different if the temperature is hot or cold, as the cubic meter will expand if the temperature is hot or become more dense if it is cold?. Also, wouldnt the cubic meter be less dense at Leadville CO where the elevation is 10000 feet as opposed to sea level. The answer is no. By convention, a standard cubic meter when expressing concentrations. The standard cubic meter is at 1 atmosphere pressure and 20^oC (68^oF).

Someone might again ask, why dont data bases express concentrations entirely in ppm or mg/m³ rather than using a mixed set of units? Answer: A lot of people favor using ppm (parts per million) when expressing concentrations of gases and organic vapors in the air. But this does not work with dusts and particulates because the weight of particulates in the air per unit volume is what is important; also, many dusts and particulates do not have a defined molecular weight. It is possible to express concentrations of gasses, vapors, metal fumes, and particulates in terms of mg/m³. But only gases and organic vapors can be correctly expressed in ppm.

Another Example: Will methanol catch fire at 60^o F (20^o C) if exposed to an ignition source (e.g. a match or a spark)?

 

When we type in methanol in the PEAC tool, the above display is seen (bottom is cropped in this illustration). Methyl alcohol is a synonym for methanol. The flash point is 52^oF meaning that methanol will ignite if the temperature is 52^oF or higher.

Another way of approaching the problem is to note that the liquid vapor pressure is 0.13 atm at 68^oF. This means that the vapor concentration just above the methanol liquid is 13%. We see that the lower explosive limit for this chemical is 6%. The chemical will ignite since actual interface concentration of 13% is greater than the lower explosive limit of 6%. In fact, if enough vapor has built up above the liquid and has not dispersed, there could be an explosion when exposed to an ignition source.

A More Complex Example: An explosive device has been detonated in a public building. Structural damage to the building appears to be minimal, at least this is an initial assessment. There is some fine dust in the air inside the building. A preliminary sample of the air inside the building showed the particulate level to be up to 50 mg/m³. Of greater concern was that that the air sample displayed an elevated radioactivity compared with background. The gamma radiation count for various air samples taken inside the building was upwards of 5000 counts per second per milliliter of sample. The energy level of the gamma radiation was 0.662 MeV, which is characteristic of a Cesium 137 fingerprint. Can a CBRN negative pressure respirator, with a particulate filter rated at 99.97% particulate removal, provide adequate protection against inhalation of Cesium 137 particulates by inhalation? How much more radiation exposure would a responder receive using a particulate filter rated at 99.97% particulate removal compared with using SCBA?

Answer: This is a much more complex situation than the previous examples, as several things must be considered. The radiation dose is a combination of gamma and beta radiation external to the body plus from any inhaled radioactive isotope. We will assume that an assessment has been made on radiation dose for emergency response personal in Level A protection using SCBA, and answer the question as to what additional radiation dose might a person receive if he/she used a particulate filter rated at 99.97% particulate removal rather than SCBA. We will assume a moderate to heavy work load resulting in a breathing rate of 65 liters/minute. The suit is assumed to adequately shield against the harmful effects of beta particles, at least for the duration of use.

What additional radiation exposure would be acceptable? For the purpose of this calculation, we will go with 5 rem (0.05 sievert) radiation dose, which is the annual inhalation limit recommended exposure by adult workers exposed to radioactive isotopes [see 10 CRF Part 20 Appendix B], over and above background [typical background is 0.3 to 0.5 rem per year]. The regulations do allow up to 100 rem exposure limit for emergency, life-saving operations, but studies have shown that there is an increased cancer risk at these higher exposure levels. The damage from radiation exposure is accumulative, meaning if someone receives a dose of 5 rem one day and another dose of 5 rem on a later date, his/her total dose is 10 rem.

OSHA regulations recommend that the particulate filter be replaced after a loading of 200 mg. Based on a breathing rate of 65 liters/minute, an ambient particulate concentration of 50 mg/m³, we can calculate the useful service life of the respirator cartridge:

Service Life (minutes) = 200 x 1000 /(65 x 50) = 62 minutes

[comment: 200 mg x 1000 liters/m³ x (1/65) minutes/liter x (1/50) m³/mg = 62 minutes]

To calculate how much additional radiation exposure the person would receive using a particulate filter rated at 99.97% removal as opposed to using SCBA (assuming the same breathing rate), we need to calculate the amount of radiation inhaled. The ambient radiation count per milliliter is 5000 per second. The intensity (% of disintegrations) of gamma radiation at 0.662 MeV is 100% (see PEAC tool display below) meaning that the number of gamma radiation counts can be equated to the number of disintegrations per second. Each count represents 1 disintegration per second, or one Becquerel. The persons breathing rate is 65 liters/minute. There are 1000 milliliters per liter. Cesium 137 is in particulate form, and we will base our calculation on 99.97% removal of Cesium 137. [1 0.9997 = 0.0003] The amount or radiation inhaled per minute is calculated to be:
 

5000 x 0.0003 x 65 x 1000 = 98000 Becquerels/minute.

The next step is to relate 98000 Becquerals/minute to the radiation exposure, in rems or sieverts. Using the PEAC tool, the annual worker dose for inhalation of Cesium 137 equivalent to 0.05 sieverts is 7.4e+006 Becquerels. Although the regulations (10 CFR Part 20 Appendix B) list 5 rem annual dose limit for workers, the 7.4e+006 in the regulations is linked to a 5 rem dose and not to time. The number 7.4e+006 is the same as 7,400,000. A person will receive a 0.05 sievert (5 rem) dose after 7400000/98000 = 66 minutes.

This number might be acceptable for an emergency situation for less than one hour, but SCBA is the better choice.

Reviewer Feedback:

A reviewer commenting on this example said that the HEPA filter standard requires a minimum filter efficiency of 99.97% for 0.3 micron particles, not 99.97% across the board. It is actually more efficient for larger particles, and since we can see the particulates as dust in the air, some of them must be larger. You really need to know the percentage of particles 0.3 microns and smaller. Also, the breathing rate of 65 liters per minute is a bit high.

Response:

The reviewers points are well taken, which illustrates the complexity of the problem. If the responder has information relating to particle size, this of course would be useful in making a decision. The assumption was made that the responder has limited information available, and that some early decisions must be made for the purpose of entry to a contaminated area. A high breathing rate was used in the example assuming that some heavy physical activity could be encountered, for example, heavy lifting as in search and rescue operations. At a later time during site decontamination and cleanup, there will be time to take more thorough measurements of radiation activity and particulate size and better define work activities. Possibly an air sampling device fitted with a HEPA filter can be rigged up, and the filtered air sample measured for radioactivity. The use of air purifying respirators may be a viable option for workers.

************************************************************************************************************

Theses examples have in common taking information out of data bases and performing some calculations or unit conversion to help in the decision process regarding action for a particular situation.