Droplet Size Distributions in the Spray from 

Commercial ‘Fogger’ Type Pepper 

Spray Products 

Dr. Alim A. Fatah* 

Cary Presser 

Process Measurement Division 

Physics Laboratory 

Edward V. White 

Analytical Chemistry Division 

Chemical Science and Technology Division 

Coordination by 

U.S. DEPARTMENT OF COMMERCE 

*Office of Law Enforcement Standards 

National Institute of Standards 

and Technology 

 Gaithersburg, MD 20899–8102 

NISTIR 7395
ABOUT THE LAW ENFORCEMENT AND CORRECTIONS 

STANDARDS AND TESTING PROGRAM

The Law Enforcement and Corrections Standards and Testing Program is sponsored by the Office of Science 

and Technology of the National Institute of Justice (NIJ), U.S. Department of Justice. The program responds to the 

mandate of the Justice System Improvement Act of 1979, which created NIJ and directed it to encourage research 

and development to improve the criminal justice system and to disseminate the results to Federal, State, and local 

agencies. 

 The Law Enforcement and Corrections Standards and Testing Program is an applied research effort that 

determines the technological needs of justice system agencies, sets minimum performance standards for specific 

devices, tests commercially available equipment against those standards, and disseminates the standards and the test 

results to criminal justice agencies nationally and internationally. 

 The program operates through: 

 The Law Enforcement and Corrections Technology Advisory Council (LECTAC) consisting of nationally 

recognized criminal justice practitioners from Federal, State, and local agencies, which assesses technological needs 

and sets priorities for research programs and items to be evaluated and tested. 

 The Office of Law Enforcement Standards (OLES) at the National Institute of Standards and Technology, which 

develops voluntary national performance standards for compliance testing to ensure that individual items of equipment 

are suitable for use by criminal justice agencies. The standards are based upon laboratory testing and evaluation of 

representative samples of each item of equipment to determine the key attributes, develop test methods, and establish 

minimum performance requirements for each essential attribute. In addition to the highly technical standards, OLES 

also produces technical reports and user guidelines that explain in nontechnical terms the capabilities of available 

equipment. 

 The National Law Enforcement and Corrections Technology Center (NLECTC), operated by a grantee, which 

supervises a national compliance testing program conducted by independent laboratories. The standards developed by 

OLES serve as performance benchmarks against which commercial equipment is measured. The facilities, personnel, 

and testing capabilities of the independent laboratories are evaluated by OLES prior to testing each item of equipment, 

and OLES helps the NLECTC staff review and analyze data. Test results are published in Equipment Performance 

Reports designed to help justice system procurement officials make informed purchasing decisions. 

 Publications are available at no charge through the National Law Enforcement and Corrections Technology 

Center. Some documents are also available online through the Internet/World Wide Web. To request a document or 

additional information, call 800−248−2742 or 301−519−5060, or write: 

National Law Enforcement and Corrections Technology Center 

P.O. Box 1160 

Rockville, MD 20849−1160 

E-Mail: asknlectc@nlectc.org

World Wide Web address: http://www.nlectc.org

This document is not intended to create, does not create, and may not be relied upon to create any rights, substantive or 

procedural, enforceable at law by any party in any matter civil or criminal. 

Opinions or points of view expressed in this document represent a consensus of the authors and do not represent the 

official position or policies of the U.S. Department of Justice. The products and manufacturers discussed in this 

document are presented for informational purposes only and do not constitute product approval or endorsement by the 

U.S. Department of Justice. 

The National Institute of Justice is a component of the Office of Justice Programs, which also includes the Bureau of Justice 

Assistance, the Bureau of Justice Statistics, the Office of Juvenile Justice and Delinquency Prevention, and the Office for Victims of 

Crime.
U.S. DEPARTMENT OF COMMERCE 

 Donald L. Evans, Secretary 

 TECHNOLOGY ADMINISTRATION 

 Phillip J. Bond, Under Secretary for Technology 

 NATIONAL INSTITUTE OF STANDARDS 

 AND TECHNOLOGY 

 William A. Jeffrey, Director 

Droplet Size Distributions in the Spray 

From Commercial ‘Fogger’ Type 

Pepper Spray Products 

 Dr. Alim A. Fatah* 

Cary Presser 

Process Measurements Division 

Physics Laboratory 

Edward V. White 

Analytical Chemistry Division 

Chemical Science and Technology Division 

Coordination by 

U.S. DEPARTMENT OF COMMERCE 

 *Office of Law Enforcement Standards 

National Institute of Standards 

 and Technology 

Gaithersburg, MD 20899–8102 

February 2007 

NISTIR 7395
ACKNOWLEDGMENTS 

The technical effort to develop this report was conducted under Interagency Agreement 2003-IJ-R-029, Project No. 

07–002. 

This report was prepared for the National Institute of Justice, U.S. Department of Justice, by the Office of Law 

Enforcement Standards (OLES) of the National Institute of Standards and Technology (NIST). 

This report was conducted under the direction of Alim A. Fatah, Program Manager for Chemical Systems and 

Materials, and Kathleen M. Higgins, Director of OLES. 
iii 

FOREWORD 

The Office of Law Enforcement Standards (OLES) of the National Institute of Standards and 

Technology (NIST) furnishes technical support to the National Institute of Justice (NIJ) program 

to strengthen law enforcement and criminal justice in the United States. OLES’s function is to 

develop standards and conduct research that will assist law enforcement and criminal justice 

agencies in the selection and procurement of quality equipment. 

OLES is: (1) Subjecting existing equipment to laboratory testing and evaluation, and (2) 

conducting research leading to the development of several series of documents, including 

national standards, user guides, and technical reports. 

This document covers research conducted by OLES under the sponsorship of the NIJ. 

Additional reports as well as other documents are being issued under the OLES program in the 

areas of protective clothing and equipment, communications systems, emergency equipment, investigative aids, security systems, vehicles, weapons, and analytical techniques and standard reference materials used by the forensic community. 

Technical comments and suggestions concerning this report are invited from all interested 

parties. They may be addressed to the Office of Law Enforcement Standards, National Institute 

of Standards and Technology, 100 Bureau Drive, Stop 8102, Gaithersburg, MD 20899–8102. 

 Kathleen M. Higgins, Director 

 Office of Law Enforcement Standards 
v

CONTENTS 

Page 

COMMONLY USED SYMBOLS AND ABBREVIATIONS...................................................... vi 

1. INTRODUCTION ..................................................................................................................1 

2. EXPERIMENTAL..................................................................................................................1 

3. RESULTS AND DISCUSSION.............................................................................................3 

4. CONCLUSIONS.....................................................................................................................6 

5. REFERENCES .......................................................................................................................7 

TABLES 

Table 1. Pepper Spray Canister Properties................................................................................2 

Table 2. Total Number of Shots per Canister with Detected Droplets .....................................4 

FIGURES 

Figure 1. a) Schematic and photograph of the overall experimental arrangement. 

 b) An expanded view of the pepper spray exiting the confinement cylinder and 

 illuminated by the laser beams of the phase Doppler interferometry (PDI) system...8 

Figure 2. Schematic of the principle of operation of the phase Doppler interferometry 

 system .........................................................................................................................9 

Figure 3. Variation of (A) droplet mean diameter and (B) streamwise velocity (U) with shot 

 number for the four canisters of group C. The open symbols referred to confined 

 cases and the closed symbols refer to the unconfined case. .....................................10 

Figure 4. Distributions for droplet A) size and B) streamwise velocity determined for shot 

 numbers 1 (initial shot) and 7 (final shot) of canister C002. ....................................11 

Figure 5. Variation of (A) droplet mean diameter and particle count and (B) streamwise 

 velocity with shot number for canister F005 (confined)...........................................12 

Figure 6A. Size distributions determined for all confined canisters in each group. ...................13 

Figure 6B. Streamwise velocity distributions determined for all confined canisters in each 

 group. ........................................................................................................................14 
vi

COMMONLY USED SYMBOLS AND ABBREVIATIONS 

A ampere Hf high frequency o.d. outside diameter 

ac alternating current Hz Hertz Ω ohm 

AM amplitude modulation i.d. inside diameter p. page 

cd candela in Inch Pa pascal 

cm centimeter IR infrared Pe probable error 

CP chemically pure J Joule pp. pages 

c/s cycle per second L lambert Ppm parts per million 

d day L Liter Qt quart 

dB decibel lb Pound Rad radian 

dc direct current lbf pound-force Rf radio frequency 

°C degree Celsius lbfin pound-force inch Rh relative humidity 

°F degree Fahrenheit Lm Lumen S second 

dia diameter Ln logarithm (base e) SD standard deviation 

emf electromotive force Log logarithm (base 10) sec. Section 

eq equation M Molar SWR standing wave ratio 

F farad m Meter uhf ultrahigh frequency 

fc footcandle μ Micron UV ultraviolet 

fig. figure min Minute V volt 

FM frequency modulation mm millimeter vhf very high frequency 

ft foot mph miles per hour W watt 

ft/s foot per second M/s meter per second λ wavelength 

g acceleration Mo Month wk week 

g gram N Newton wt weight 

gr grain Nm Newton meter yr year 

H henry Nm nanometer 

h hour No. number 

area=unit2 (e.g., ft2

, in2, etc.); volume=unit3 (e.g., ft3, m3, etc.) 

PREFIXES COMMON CONVERSIONS (See ASTM E380)

 

d deci (10-1) Da deka (10) 0.30480 m =1 ft 4.448222 N = 1 lbf 

c centi (10-2) H hecto (102

) 25.4 mm = 1 in 1.355818 J = 1 ftlbf 

m milli (10-3) K kilo (103

) 0.4535924 kg = 1 lb 0.1129848 N m = 1 lbfin 

μ micro (10-6) M mega (106) 0.06479891 g = 1 gr 14.59390 N/m = 1 lbf/ft 

n nano (10-9) G giga (109

) 0.9463529 L = 1 qt 6894.757 Pa = 1 lbf/in2

p pico (10-12) T tera (1012) 3600000 J = 1 kWhr 1.609344 km/h = 1 mph 

 psi = mm of Hg x (1.9339 x 10-2) 

 mm of Hg = psi x 51.71 

Temperature: T °C = (T °F –32)×5/9 

Temperature: T °F = (T °C ×9/5)+32 
1

DROPLET SIZE DISTRIBUTIONS IN THE SPRAY FROM COMMERCIAL

‘FOGGER’ TYPE PEPPER SPRAY PRODUCTS

This report documents a preliminary investigation of the measurement of droplet sizes

in the spray from four commercial ‘fogger’ type pepper spray products. Droplet sizes

were measured over the range of 2 μm to 120 μm by phase Doppler interferometry at

a distance from the canisters similar to that expected when the spray is used as a 

defensive weapon.

1. INTRODUCTION

Commercial pepper spray devices are available that deliver a coherent liquid stream or a fine 

aerosol from the nozzle. These sprays contain, as the active ingredient, oleoresin capsicum

(OC), a chemically complex extract from hot peppers, or a synthetic chemical, nonivamide, that

is present as a minor component in OC. They may also contain a variety of solvents, carriers, 

and surfactants. During the use of pepper sprays to assist in subduing violent individuals, it is 

likely that some of the droplets are inhaled. Therefore, it is potentially useful to determine the 

size of the droplets since smaller droplets penetrate deeper in to the lung and therefore may

present a greater hazard [1]1. For environmental monitoring purposes droplets are often classified

in three size ranges: Droplets larger than 10 μm which do not reach the lungs and are generally

not health hazards; droplets with sizes equal to or less than 10 μm (PM10) that reach the upper 

airways of the lung; and droplets with sizes equal to or less than 2.5 μm (PM2.5) that reach the 

alveoli and are thought to be the most hazardous [2].

This preliminary study examined how the droplet size, the number of particles, and the velocity, 

changed as successive shots were fired from four commercial ‘fogger’ type pepper spray

products.

2. EXPERIMENTAL

Samples

Four commercially available pepper sprays were tested as listed in Table 1.

 

1

See References on page 7. 
2

Table 1. Pepper Spray Canister Properties 

Canister

Group

Company Model Solvent

(Propellent)

Solvent 

Refractive 

Index

Expiration

Date

B ZARC International, 

Inc.

Cap-Stun2

Standard Duty, 

Z-305, 1 oz

Isopropanol*

(Isobutane)

1.378 12/2008

C Defense Technologies/Federal Laboratories

BodyGuard

LE-10, Cone,

3.17 oz

Diethyleneglycol 

n-butylether**

(unknown)

1.431 2008

D Guardian Personal 

Security Products, 

LLC

BodyGuard

LE-10, Cone,

1.5 oz

Diethyleneglycol 

n-butylether**

(unknown)

1.431 2006

F Aerko International, 

Inc.

PUNCH II M4, 83 g

Isopropanol*

(Isobutane/Propane)

1.378 06/2007

Note: The same model names and numbers, but different company names, for C and D

are correct. * Information on Canister **Information from Material Safety Data Sheets

Test Apparatus for Firing Canisters

Canisters were mounted on a stand similar to that described in [3]. The apparatus allowed

repeated firing for 1 s at 1 min intervals. The canister nozzle was located 1.83 m (6.0 ft) from the

point where measurements were made. Since the unconfined canister sprays dispersed quickly, a

cylinder of polyvinyl chloride (PVC) pipe, 76 mm (3 in) diameter and 1.52 m (5 ft) in length, served

to confine the spray to a narrower cross section in order to obtain sufficient data for droplet diameter

measurements. The cylinder was centered between the mounted pepper spray canister and the probe

volume of a phase Doppler interferometer (PDI), which was used to measure the spray characteristics. There was significant impingement of the spray on the inside cylinder surface, which resulted

in liquid accumulation inside the cylinder. It was assumed that there was no preferential biasing of

the measurement (e.g., droplet coalescence) as a result of the confinement. The stand and probe 

volume were inside a ventilated chamber. The PDI was outside of the ventilated chamber. The 

arrangement of the experimental apparatus is shown in figure 1.

 

2

 Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such

identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to

imply that the materials or equipment identified are necessarily the best available for the purpose.
3

Phase Doppler Interferometry

Phase Doppler interferometry [4] has been used to characterize sprays in a wide variety of areas

including spray combustion, spray coatings, agricultural pesticides, fire suppression, and others. This

measurement technique is an extension of laser Doppler velocimetry that measures droplet size as

well as velocity [5-7]. Phase Doppler interferometry involves creating an interference pattern in the

region where two laser beams intersect, which results in a region of alternating light and dark fringes

called the probe volume. Due to the interference pattern, a droplet passing through the probe volume

scatters light that results in a modulated signal at the detectors (see Fig. 2). This signal is characteristic of the droplet size, refractive index, and velocity. For a droplet with known refractive index, the

size and velocity can be determined. Bachalo [8] published a review of PDI and its application to the

study of aerosolized flows.

Measurements were done using a two-component phase Doppler interferometer with a 5 W argon

ion laser as the illumination source. To accommodate the horizontal orientation of the experimental

apparatus, the transmitter and receiver were positioned in a vertical plane as shown in figure 1. The

optical arrangement remained unchanged (including the scattering angle of 30°) for all of the 

experiments. Droplet size and velocity distributions were obtained at one point in the center of the

spray. The time interval over which the actual data were collected was 1 s, that is the duration of

one canister shot, however, the PDI data acquisition was initiated before the canister valve was

opened, and terminated after the pulse of spray was transported past the PDI laser beams. The 

measurements were corrected for the solvent refractive indices (see Table 1).

3. RESULTS AND DISCUSSION

Measurements of the droplet mean diameter (i.e., Sauter mean diameter [9]), streamwise velocity,

and cross-stream velocity were made on successive 1 s bursts separated by 1 min for 15 canisters

representing four models (denoted as groups B, C, D, and F) from three manufacturers. Each canister test consisted of depressing the canister nozzle for a 1 s shot, recording the spray characteristics

with the PDI system, and repeating the sequence at 1 min intervals until the canister was empty (i.e.,

no droplets were detected by the PDI). Three canisters from each group were examined using the

spray confinement cylinder since the unconfined spray did not reach the required 1.8 m (6.0 ft) 

distance in a sufficiently predictable direction to produce reliable detection of the droplets without it. 

One additional canister from each of groups B, C, and D was examined without the spray confinement cylinder.

Shot-to-Shot Variations

Shot-to-shot variations are discussed for groups C and F. The total number of shots per canister

for each group is given in Table 2. Results for the mean diameter and streamwise velocity with shot 

number are presented in figure 3 for the four canisters of group C. When the spray was directed 

through the spray confinement cylinder, the number of droplets transported through the PDI probe
4

Table 2. Total Number of Shots per Canister with Detected Droplets 

Canister

Group

Total Number of Shots

(Confined Cases)

Total Number of Shots

(Unconfined Cases)

B 6 5

C 7 2

D 3 - 5 3

F 59 - 63 -

volume was increased significantly. The mean diameter was fairly constant per shot until when

nearly all of the liquid contents were exhausted from the canister (see Fig. 3A). The mean 

diameter was fairly constant per shot until nearly all of the canister contents were expelled. The

value of the mean diameter for the unconfined case (closed symbols) was always lower than

for the confined cases, which was attributed to deceleration and dispersion of the droplets with 

increasing streamwise distance. As shown in figure 3B, the mean streamwise velocity is about 

14 m/s for the confined cases and decreases with increasing shot number. For the unconfined

case, the initial mean velocity was about 1 m/s, having little momentum to reach the target. 

Since measurements were carried out only at the center of the spray, it is unknown what the

droplet radial spatial profiles may reveal regarding transport of the spray off-axis. Determination

of the droplet diameter and velocity distributions at several radial positions would require simultaneous off-axis measurements, which was beyond the scope of this study.

Figure 4 presents the distributions for droplet diameter and streamwise velocity for the first shot

of canister C002 (see Fig. 3), which represents a typical 1 s first shot. Also shown in figure 4 is the 

last shot that gave measurable results. The distributions initially (see Fig. 4A, shot number 1) included

droplets ranging from about 100 μm down to a few micrometers (at the detection limit of the instrument). For the nearly depleted case (see Fig. 4A, shot number 7), all of the detected droplets are

smaller than 40 μm. One may speculate that for this shot either the remaining liquid in the canister is

well atomized by the gas propellant, or any larger droplets are transported off-axis and were not 

detected since our measurements were near the center of the spray. Such spray characteristics are

typical of certain classes of atomizers [9], for which the smaller diameter droplets are transported essentially along the spray axis, i.e., in the direction along which the canister is pointed, and larger 

droplets near the spray periphery (boundary). The values of the streamwise velocity decrease, and the

distribution becomes narrower, as the canister is emptied.

Figure 5 presents the variation of the mean diameter and streamwise velocity with shot number

for group F. This group produced more shots with less liquid per shot (about half the number of 

droplets per shot) than the other groups. The variation in the results for droplet mean diameter

(see Fig. 5A) increases significantly as the shots progress. Figure 5A also presents the droplet 

number count for each shot. As the shots increase, the number count decreases. When the number

of detected droplets (counts) is below 200, the variation in the mean increases significantly, 

making it difficult to discern trends. For example, examination of the size distributions indicates

that for shot numbers 57 and 59 (indicated by the two solid arrows) the presence of outliers 
5

increases the value of the mean diameter dramatically above what the value would be without the

outliers. Low values of the mean diameter are indicative of the lack of data for that shot (see shot

numbers 58 and 60, indicated by the dashed arrow).

Differences Between Canister Groups

For each group, the variation of the droplet diameter and velocity from canister to canister was

small when the spray was transported through the confinement cylinder. The amount of spray 

reaching the target from the specified distance was smaller for the unconfined canisters than for

the confined canisters. The number of droplets detected for the unconfined sprays of groups B,

C, D was 4.4 % to 4.7 %, 1.4 % to 3.2 %, and 51 % to 70 % of that observed for the confined 

sprays. On a weight basis, this corresponds to 0.0009 % to 0.001 %, 0.0001 % to 0.0025 %, and

9 % to 30 %. Although the number of detected droplets for the unconfined canister D004

(relative to the confined canisters) is much larger than for groups B and C, the total number of 

detected droplets for confined cases of group D relative to groups B and C was much less, i.e., 47 %

and 37 %, respectively. Part of the reason why the number of detected droplets was higher for

the unconfined canister D004 was because of the higher mean streamwise velocity of 4.4 m/s, as 

opposed to 1 m/s for canister C003. The velocity distribution is also broader with a maximum 

value reaching 11 m/s, as opposed to 3 m/s for canister C003.

A picture of the general spray characteristics for a canister group is presented by combining the 

results for the three confined canisters of each group. Figure 6 presents distributions for the 

droplet diameter and streamwise velocity for the confined cases of each group. The largest 

droplet diameters detected were about 120 μm and for some groups the distributions were 

bimodal. The distributions for the individual confined canisters of a particular group are similar

to each other, i.e., similar to its group distribution presented in figure 6A. The bimodal nature of

the diameter distributions was attributed to changes in the distribution between the initial and 

final shots. The variation in streamwise velocity between canister groups is presented in figure 6B, 

with only group D having a bimodal distribution to correlate with the bimodal diameter 

distribution.

The maximum particle count for group F (Fig. 6A) is much higher than for the other groups. As 

mentioned above, the number of shots for group F (over 60 shots) was much larger than for the 

other groups (ranging from 3 shots to 7 shots) although the number of detected droplets per shot 

was less than half (see Fig. 5A). The total number of droplets detected for group F was more 

than 10 000 droplets per canister, which was at least three times larger per canister than the other 

groups. Comparing the number of droplets less than 10 μm (i.e., those droplets with a higher 

probability of inhalation) to the total particle count indicates that 28 % to 35 % of the droplets 

were smaller than 10 μm on a number basis and 0.03 % to 0.08 % on a mass basis for the 

confined group F. For the other groups, the percentages were 9 % to 15 % on a number basis 

and 0.001 % to 0.004 % on a mass basis.
6

4. CONCLUSIONS

Droplet size and velocity measurements were carried out using phase Doppler interferometry in the

center of sprays generated from commercial 'fogger' type pepper spray canisters. Four different

groups of canisters were fired for which the spray characteristics were obtained under both confined

and unconfined conditions. The results indicated that canister-to-canister variations of droplet 

diameter were small within a particular group. The droplet diameter and velocity distributions were

substantially different for each group. The mass fraction of droplets with diameters less than 

10 μm, which is the droplet diameter that could carry potentially toxic material to the lungs, was 

0.001 % to 0.08 % for the four canister groups measured.
7

5. REFERENCES

1. Longest, P.W., and Kleinstreuer, C., 2005. Computational models for simulating multicomponent aerosol evaporation in the upper respiratory airways. Aerosol Science and Technology,

39, 124-138.

2. Fay, J.A., and Golomb, D.S., 2002. Energy and the Environment, Oxford University Press, 

New York, 231-232.

3. National Institute of Justice. September 1985. Hand-Held Aerosol Tear Gas Weapons, 

Technology Assessment Program, NIJ Standard 0110.00. Washington, DC, U.S. 

 Government Printing Office.

4. Widmann, J.F., Presser, C., and Leigh, S.D., 2001. Improving phase Doppler volume flux 

measurements in low data rate applications. Measurement Science Technology 12, 1180-

1190.

5. Durst, F., and Zare, M., 1975. Laser Doppler measurements in two-phase flows.

Proceedings of the LDA Symposium. Copenhagen, 403-29.

6. Bachalo, W.D., and Houser, M.J., 1984. Development of the phase/Doppler spray analyzer

for liquid droplet size and velocity characterizations. AIAA/SAE/ASME 20th Joint Propulsion

Conference.

7. Bachalo, W.D., and Houser, M.J., 1984. Phase/Doppler spray analyzer for simultaneous 

measurements of droplet size and velocity distributions. Opt. Eng. 23, 583-90.

8. Bachalo, W.D., 1994. Experimental methods in multiphase flows. Int'l J. Multiphase Flow

20, 261-95.

9. Lefebvre, A.H., Atomization and Sprays, Hemisphere, New York, 90-92.
8

Canister

PDI

Transmitter

Confinement

Cylinder

PDI

Receiver

a

PDI

Transmitter

Confinement

Cylinder

Illuminated

Spray

b

Figure 1. a) Schematic and photograph of the overall experimental arrangement. b) An

expanded view of the pepper spray exiting the confinement cylinder and illuminated by 

the laser beams of the phase Doppler interferometry (PDI) system.
9

DET 1

DET 2

DET 3

DET 1

DET 2

DET 3

LASER

MEASUREMENT 

VOLUME

DETECTOR 1

DETECTOR 2

BEAM SPLITTER 

AND

FREQUENCY SHIFT 

MODULE

DETECTOR 1

DETECTOR 2

DETECTOR 3

DETECTOR 3

Figure 2. Schematic of the principle of operation of the phase Doppler interferometry system.
10

A

B

Figure 3. Variation of (A) droplet mean diameter and (B) streamwise velocity (U) with shot

number for the four canisters of group C. The open symbols referred to confined cases 

and the closed symbols refer to the unconfined case.
11

Shot Number 1 Shot Number 7

A

B

Figure 4. Distributions for droplet A) size and B) streamwise velocity determined for shot

numbers 1 (initial shot) and 7 (final shot) of canister C002.
12

A

B

Figure 5. Variation of (A) droplet mean diameter and particle count and (B) streamwise 

velocity with shot number for canister F005 (confined).
13

Figure 6A. Size distributions determined for all confined canisters in each group.
14 

Figure 6B. Streamwise velocity distributions determined for all confined canisters in each group.