La. Admin. Code tit. 33, § III-2901 - Odorous Substances

A. Purpose. The purpose of this Chapter is to establish an ambient air standard for odors.

B. Scope. This Section is applicable to all sources which emit odorous substances into the ambient air except those exempted in LAC 33:III.2901.E.

C. Definitions

Odor Dilution Ratio-the dilution of a sample required to reach a given odor intensity level, detectability point, sensory target, etc. This is represented by Z_t.

Z_t = C_o/C_t

where:

C_o = the odorant concentration (of the sample); and

C_t = the odorant concentration when some sensory target has been reached, such as the odor threshold.

Perceived Odor Intensity-the intensity of an odor sensation which is independent of the knowledge of the odorant concentration.

D. Standard. Limit on Odorous Substances at or beyond Property Lines. A person shall not discharge an odorous substance which causes a perceived odor intensity of six or greater on the specified eight point butanol scale when determined by the department's test method. (Method 41)

E. Exemptions. The following buildings, materials and operations are exempted from the provisions of this regulation:

1. single family dwellings;

2. restaurants;

3. other establishments for the purpose of preparing food for human consumption;

4. materials odorized for safety purposes;

5. materials possessing strong odors for reasons of public health and welfare where no suitable substitute is available and where best modern practices are employed;

6. agricultural, fiber, timber, poultry, seafood or fisheries production, unless such odors are detected in concentrations or intensities above that normally detected from these processes or byproducts when using applicable air pollution control devices; and

7. emission points regulated under the Total Reduced Sulfur (TRS) emission standard (LAC 33:III.2301.D.3).

F. Sample Analysis

1. Collection of Samples. Samples shall be taken and transported in a manner which minimizes alteration of the samples either by contamination or loss of material.

2. All samples shall be evaluated as soon after collection as possible in accordance with the procedures set forth in Subsection G of this Section.

G. Method 41-Odor Test Methods

1. Butanol Odor Evaluation Procedure

a. Sampling and Storage. Odorous gas sampling is no more than typical integrated bag sampling. Figure l shows the sampling train used by the department. A sample bag is placed inside the rigid leak-proof container. Bag material shall be manufactured of FEP Teflon, Tedlar, or Mylar.

b. The bag is filled by partially evacuating the rigid container. After partial filling, the air in the bag is expelled by pumping air into the container until the bag is empty. This serves to precondition the bag walls.

c. The bag is then totally filled by evacuating the container with a pump. The bag is removed, capped or sealed, and tagged for storage and eventual transport to the odor lab for sample evaluation. See Figure l for apparatus setup.

d. If the odorous air is very humid, and it is suspected that condensation of water will occur in the bags, an additional procedure, predilution, can be used to prevent condensation. The bag is half filled with odor-free air using a cylinder and flowmeter. This will allow exact metering of a known amount of odor-free air; the odorous air sample can then be taken per previous instructions.

e. Odorous samples should be stored in containers for a minimum of time after collection. This should be adhered to wherever possible and the time of storage, before odor measurement, must be recorded for each sample. Ideal storage conditions are less than four hours; acceptable conditions for most odor mixtures are 8-16 hours. Storage over 24 hours is unacceptable. In general, to prevent sample deterioration:

i. use FEP Teflon, Tedlar, or Mylar bags;

ii. minimize sample storage time; and

iii. predilute sample bag or use other suitable means to remove moisture if condensation is evident on the bag wall.

2. The department uses butanol referencing techniques for quantifying odors in terms of intensity. The method parallels that specified in ASTM E544-75. A complete description of the method follows.

a. Description

i. Figure 2 depicts the olfactometer. Adjustable air flow controls are mounted on the rectangular base plate. The odorant vapor generator, flow splitters, and ports that deliver the prepared stimuli (butanol) are mounted on an aluminum plate disc that can be rotated within an almost full revolution. A handle is positioned to turn the sample ports and is set to limit the rotation of the disc to one turn.

ii. There are two air flow systems within the olfactometer, each is controlled by a separate valve (V) and monitored by separate in-line flowmeters (F₁, F₂). Both can be supplied from the same air supply.

iii. Odorant vapor flow system is supplied with air at a rate of 350 ml/min (left flowmeter). This air flow is delivered to the odorant vapor generator through a flexible food-grade (almost odorless) Tygon tubing (T). The odorant vapor generator consists of a glass vessel (G) and several flow-controlling capillaries. This section is shown separately schematically in Figure 3.

iv. The odorant vapor/air mixture from the generator is supplied to the upper cavity of the "odor splitter" (O) through the upper tubular spout of this splitter. The splitter distributes the generator-prepared vapor/air mixture to eight stainless steel capillaries. The other ends of the capillaries connect via Teflon tubing to the corresponding glass sniffing ports. The capillaries are calibrated so that Port Number 8 (highest odorant concentration) receives mominally 160 ml/min of the vapor/air mixture, and the next Port, Number 7, receives nominally 80 ml/min of the same mixture. Other ports receive odorant volumes as per Table l.

v. The make-up air flow system, which is controlled by the valve-Flowmeter assembly (F₂), is fed at 950 ml/min. It is distributed by the lower level of the splitter (O). The make-up air is delivered to this level via Tygon tubing attached to the spout of the splitter under the olfactometer disc. There is no connection between the lower level and upper level of the splitter. The lower splitter provides additional air to Ports Number 7 through Number 1 so that the total flow to each port is nominally 160 ml/min. Mixing occurs in the port. Rapid flow rate changes occur on emergence from the Teflon tubing and from the lower smaller cross section of the glass port into the wider vertical glass tube portion. This action assures sufficient turbulence for adequate mixing.

(a). Flow rates are measured, if necessary, by attaching a Buck Calibrator flowmeter to ends of the Teflon tubings temporarily pulled out of the ports. Nominal flow rates should be:

Table 1
	Odorant Vapor-Carrying Tubing End	Make-Up Air
Port Number	Tubing End (ml/min)	Tubing End (ml/min)
8	160
7	80	80
6	40	120
5	20	140
4	10	150
3	5	155
2	2.5	157.5
1	1.25	158.5

(b). The actual flow rates may differ, usually not more than within a few percent, and are measured and included in calculations in more exact experiments.

vi. Vapor generator section, Figure 3, contains a saturator, (Vessel G) which consists of a horizontal 16 mm o.d. by 170 mm long Pyrex tube with closed ends and three side tubes, each 4 mm o.d. and 25 mm long. The middle tube is used to introduce the odorant (butanol) and is then closed with a glass rod plug, P, connected to the side tube by a short length of black neoprene tubing.

vii. Important Safety Note. When slipping the neoprene tubing onto the glass side tubes, hold the side tube with fingers using short neoprene tubing collar with which the tube is equipped. Twist the attachable neoprene tubing to and fro, to facilitate the connection. If the glass vessel is held instead, the small glass side tubes may break off. Use the same precautions when removing the attachable tubing. Same applies to the other glass tubing/neoprene slip-on connections. Collars are not shown in Figure 3.

viii. The two other glass side tubes on the vessel are connected to the flow control capillaries. Capillary C is the principal vapor flow control capillary, while Capillary E is simply an exit capillary, with much less flow resistance than C. Capillary B is for air bypass; it is always of the same size and length, while Capillary C may be changed to provide 5x, 25x, 50x, and 100x flow split ratio. The department will use the nominal 5x flow split ratio in establishing its butanol scale. The ratio of flow rates through bypass B and through the saturator vessel vapor space depend on the flow resistances of B and C. Capillary C is upstream of the vapor space to maintain air pressure in the saturator vessel close to atmospheric.

ix. The desirable volume of odorant in the saturator vessel is 8-10 ml, which fills the lower half of the vessel and provides the widest surface. At up to 60 ml/min air flow, the air leaving the saturator is practically saturated with the odorant vapor, as has been established by mass-transfer calculations and direct measurements of l-butanol concentrations by hydrogen flame ionization detector; at 60 ml/min, 98 percent plus saturation is reached. The degree of saturation is not a function of the vapor pressure (which varies with odorants by several orders of magnitude), but of the diffusion constant for the odorant in air, and this constant varies from odorant to odorant within a fraction of one order of magnitude. The method of air passage over the surface circumvents the need for mist filters needed when the saturation is by bubbling the air through the odorant. At lower flow rates, a few drops of the odorant may provide enough evaporation surface.

x. Vaporization rates are too low to produce significant cooling except for the most volatile odorants. Hence, for simplicity, no thermostating is provided, but the temperature at the saturator vessel is measured for use in vapor pressure calculations. The temperature in the area of the apparatus will be maintained at 25°C.

xi. The vapor dilution immediately after the saturation in the vessel produces a margin of safety in preventing condensation in the 8-way splitter, in case of a temperature change or sudden pressure drop.

xii. Connections to the stainless steel capillaries are via slip connectors, as shown in Figure 3. A short (5 MM) length of food-grade Tygon tubing fits tightly around the Capillary. A piece of black neoprene tubing overlaps this tubing and the larger connecting tube (brass tee, or glass side tube, or multi-way air or odorant-side splitter) so that the small Tygon tubing fits tightly against the larger tube. This system permits only a limited contact between the odorant vapor and Tygon and neoprene. These materials can be reached by vapors only by a non-connective diffusion through stagnant annular space between the o.d. of the capillary and the larger connecting tube; thus, depletion of vapor by sorption into Tygon or neoprene is negligibly small. In reverse, when the odorant vapor is discontinued, contamination of air flow by desorption of the odorant from Tygon or neoprene is slow and usually does not generate a prolonged contamination problem of any significance. Still, it is desirable to flush the odorant vapor flow system during the shutdown.

xiii. Connections between B and E Capillaries are via brass tees and slip on connectors. To check the generator system splitter ratio, brass tee (T) is pulled off B and E, and the flow rates out of B and E are measured using the same total odorant vapor flow rate as normal (the splitter ratio may be slightly affected on the absolute flow rates).

xiv. Important-only soap film flowmeters are suitable for measuring the flow rates in ports and at B and E. Other flowmeters produce some flow resistance which, in the low-pressure flow system of the olfactometer, will influence the flow rates and yield wrong values. Figure 3, bottom, illustrates connections to the soap film flowmeter for two situations:

(a). connecting to Teflon tubing ends pulled backward out of the ports for measuring flow rates to the ports; and

(b). connecting to ends of B or E when the brass Tee (Figure 3) is pulled off for measuring the flow rates from B and E, to check split ratio in the vapor generator section.

xv. Very Important-to Prevent Undesirable Contamination of the System

(a). With the odorant in the vapor-generating vessel, the flow of air to the odorant part of the system must be immediately set in operation. If this is not done, odorant vapors from the vessel may drift into the splitter bypass, condense there, and result in a much higher odorant concentration than in the regular operation. It is best to place the odorant into the vessel through the center spout (cf. Figure 3) with the bypass system (two brass tees with Capillaries B, C, and E attached) removed from the vessel, then plug the center spout of the vessel, begin air flow and then connect the bypass system to the vessel.

(b). The same applies to shutting-down of the olfactometer. First, the by-pass system is removed from the vessel, and the end spouts of the odorant vessel are plugged with pieces of neoprene tubing and glass rod plugs. With air flow still continuing, the Capillary C is connected to Capillary E by a short piece of Teflon tubing. This permits flushing the odorant vapors from the odorant side of the system. Flushing is continued until the highest-concentration port does not exhibit odor.

3. Problems/Backflow. Failure to observe need for continuous air flow while the odorant vessel is connected to the splitter (see preceding section) can easily result in diffusion of the odorant throughout the system, including back-diffusion into the Tygon tubing connecting flowmeter to the disc assembly. Such contamination is difficult to remove, and replacement of some components may become necessary. A list of sources for the components is attached (Paragraph G.5 of this Section).

4. Sample Calculation of Dilutions

a. Saturated Butanol

i. Odorant: l-Butanol

ii. Temperature: 25°C

iii. Vapor pressure, from Chemistry and Physics Handbook or other source, for 25°C is 6.97 mm.

iv. This corresponds to:

l,000,000 x 6.97/760 = 9170 ppm in air saturated with l-butanol vapor at 25°C; (l atm = 760 mm).

b. Dilution Factor in Generator/Bypass System. Dilution Factor: 4.66 +- .20

i. The concentration of l-butanol in the flow supplied to the round splitter is then:

9170/4.66 = 1966 +- 16 ppm

ii. This is also the concentration supplied to Port Number 8.

iii. Measurements for other ports are conducted by pulling the Teflon tubing out from the ports and connecting the Buck calibrator to these lines.

iv. The following set of data illustrates the calculations. (See Table 2)

v. The brass tee is sequentially pulled off Capillaries B and E and the air flow from each is measured.

5. Components and Sources

a. Stainless Steel Capillaries

i. l/16 o.d., 0.030 i.d.

ii. l/16 o.d., 0.020 i.d.

iii. l/16 o.d., 0.010 i.d.

b. Teflon Tubing. Teflon tubing AW Gage Number 15, standard wall, natural color.

c. Tygon Tubing

i. Tygon Food Grade 0.0315 in. i.d. For slip-on-connectors for stainless steel capillaries.

ii. Tygon tubing, Food Grade Formulation B-44-4X, 5/32 in. i.d., 7/32 in. o.d., l/32 in. wall. For flowmeter-to-disc connection.

iii. Tygon Food Grade tubing, 0.0655 in. i.d., 0.1945 in. o.d. For connection of soap film flowmeter tubing to Teflon tubing ends.

d. Neoprene Tubing. Black neoprene tubing, l/4 in. o.d., l/16 in. wall, for slip-on connectors and for plug.

e. Glass Ports, Odorant Vessel. Pyrex glass, custom-made by glass blowers.

f. Flowmeters

i. 50-500 cc/min

ii. 100-1000 cc/min

Table 2 8-Port 1-Butanol Olfactometer Port Concentration in ppm
Date	7	6	5	4	3	2	1
12-13	1038	533	274	138	70	35	17
12-15	1034	517	272	137	71	34	18
12-15	1042	524	268	137	71	34	19
12-15	1042	520	271	132	72	35	18
12-16	1010	513	271	136	70	35	17
12-16	1040	529	278	137	73	36	18
12-16	1032	516	272	134	72	35	18
Total	7238	3652	1906	951	499	244	125
Avg.	1034	522	272	136	71	35	18
	+-10	+-7	+-3	+-2	+-1	+-1	+-1

6. Odor Panel

a. An odor panel consisting of eight members shall be selected by the department. Panelists shall not use perfume or perfumed shaving lotion within two hours prior to the test. Panelists shall not smoke, eat, or chew tobacco or gum for at least one hour before testing. Panelists shall not be tested for prolonged periods of time. A loose schedule with long resting periods for panelists is recommended.

b. Panelist candidates are screened for their ability to judge intensity. This is usually done using the butanol intensity olfactometer. A bag sample is taken from one of the eight butanol ports (usually Number 4 or Number 5) and the candidate must sniff the bag sample and select the port they feel has the same intensity. Panelists should be able to match butanol-to-butanol within two scale units. As with all sensory odor evaluations, the screening tests should be conducted in as nearly an odor-free environment as possible.

c. The testing room will be supplied with activated carbon filtered air of controlled constant temperature and humidity (25°C and RH 50 percent).

d. Each panelist compares the intensity of the undiluted ambient sample being evaluated to the eight point butanol scale, specified in this procedure starting from the low end of scale, i.e., levels between two values on the scale may be selected by each panelist (i.e., 2.5, 6.5, etc). The arithmetic average of the values chosen by the eight panelists will determine compliance with the standard specified in the regulations.

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Notes

La. Admin. Code tit. 33, § III-2901

Promulgated by the Department of Environmental Quality, Office of Air Quality and Nuclear Energy, Air Quality Division, LR 13:741 (December 1987), amended by the Office of Air Quality and Radiation Protection, Air Quality Division, LR 22:1212 (December 1996), amended by the Office of Environmental Assessment, Environmental Planning Division, LR 26:2460 (November 2000).

AUTHORITY NOTE: Promulgated in accordance with R.S. 30:2054.