U.S. Department of Justice

Office of Justice Programs

National Institute of Justice

R e s e a r c h i n B r i e f

National Institute of Justice

December 2001

continued...

Issues and Findings

Discussed in this Brief: The

effect of oleoresin capsicum (OC),

or pepper spray, on respiration,

particularly when combined with

positional restraint. Researchers

exposed 34 subjects to OC spray,

both while sitting and in the

prone maximal restraint position.

Key issues: OC spray has gained

wide acceptance in law enforcement as a swift and effective way

to subdue violent and dangerous

suspects in the field with relatively little force. As its use has

increased, however, OC spray has

been associated in the media

with the deaths of a number of

suspects in custody. Some have

argued that OC spray, when used

in combination with physical

restraints, can lead to significant

respiratory compromise, including

asphyxiation and death. To test

this theory, researchers examined

the respiratory effects of inhaling

OC spray while in the sitting and

restraint positions and compared

the results with those obtained

in the same two positions when

subjects inhaled a placebo spray.

Key findings: OC exposure and

inhalation do not result in a significant risk for respiratory compromise or asphyxiation, even when

combined with positional restraint.

● In the sitting position, OC spray

inhalation and exposure resulted

in no respiratory compromise.

Support for this research was provided through a transfer of funds to NIJ from 

the Office of Community Oriented Policing Services.

Most law enforcement agencies in the

United States have authorized the use of

oleoresin capsicum (OC), or pepper spray,

as a use-of-force option to subdue and

control dangerous, combative, or violent

subjects in the field. OC, with its ability

to temporarily incapacitate subjects, has

been credited with decreasing injuries

among officers and arrestees by reducing

the need for more severe force options. 

Despite the success of OC spray, there

is growing concern about its safety, particularly when exposure is combined with

positional restraint. A number of arrestees

exposed to OC, which induces coughing,

gagging, and shortness of breath, have

died in custody—thus prompting the allegation that OC inhalation places individuals at risk for potentially fatal respiratory

compromise.1

The National Institute of Justice (NIJ), in

conjunction with the Office of Community

Oriented Policing Services (COPS), supported a study by medical researchers

at the University of California–San Diego

to examine the combined effects of OC

exposure and positional restraint on respiratory and pulmonary function among

34 volunteer subjects recruited from a

law enforcement training academy.

Research findings suggested that inhalation of OC spray does not pose a significant

risk to subjects in terms of respiratory

and pulmonary function, even when it

occurs with positional restraint. However,

OC exposure did result in a small but

statistically significant increase in blood

pressure, the origin of which remains

unclear.

What is OC spray? 

Oleoresin capsicum is the oily extract

of the cayenne pepper plant. Exposure to

OC irritates the skin, eyes, and mucous

membranes of the upper respiratory tract.

These properties of the pepper plant have

been known for centuries. In Japan, samurai warriors threw rice-paper bags filled

with pepper extracts at the eyes of their

enemies to cause temporary blindness.

Chinese soldiers heated red peppers in

hot oil to form an irritant smoke to be

blown over enemy lines.

In 1973, OC became available as an

aerosol spray and was initially used by

FBI personnel and U.S. mail carriers to

incapacitate humans and animals on a

temporary basis. During the late 1980s,

it was widely adopted by law enforcement agencies nationwide and was made

Pepper Spray’s Effects on a

Suspect’s Ability to Breathe 

By Theodore C. Chan, Gary M. Vilke, Jack Clausen, Richard Clark, Paul Schmidt, 

Thomas Snowden, and Tom Neuman

 COMMUNITY ORIENTED POLICING SERVICES

U.S. DEPARTMENT OF JUSTICE
2

R e s e a r c h i n B r i e f 

There was no evidence of abnormally low oxygen levels or abnormally high levels of carbon dioxide

(CO2). In fact, the lower CO2 levels for this group suggest that OC

spray may actually increase ventilation slightly.

● Researchers detected no difference between the OC and placebo groups in the restraint position.

There was some decline in pulmonary function, but not enough

to be clinically significant. As in

the sitting position, OC seemed

to increase ventilation.

● OC exposure did, however,

result in an increase in blood

pressure, perhaps due to the discomfort and pain associated with

OC. The clinical implications of

this finding remain unknown.

● This study had a number of

limitations. First, not all of the

conditions that occur when OC

and restraint are employed in the

field could be reproduced in the

laboratory. Second, the effects

of prolonged sprays or repeated

exposures were not studied.

Third, all of the subjects were

cadets at the local police academy and were generally healthy.

Fourth, the study did not investigate the long-term effects of OC

exposure or the potential for complications from chronic occupational exposure to OC.

Target audience: Law enforcement policymakers and practitioners, defense and prosecution

attorneys involved in OC spray

criminal and civil litigation, and

medical examiners.

Issues and Findings

...continued

available for use by the general public.

Currently, hand-held canister spray models are produced and used in this country.

These models produce an aerosol, liquid

stream, or foam spray, with OC concentrations ranging from 1 to 10 percent.

Pepper sprays are generally regarded

as immediately effective, safer, and less

toxic than other classic forms of tear gas

or mace, such as chloroacetophenone (CN)

or o-chlorobenzyildene malononitrile (CS).

About this study

Previous studies have examined the

cough-inducing properties of capsaicin

(the active ingredient of OC) spray, and

a few have looked at the health effects

of OC in humans. In addition, some research has been conducted to determine

if prone maximal restraint (the “hogtie”

or “hobble” position) may lead to positional asphyxia (death caused by obstructed airways or other interference with

breathing resulting from body position).

The study discussed in this Research in

Brief is the first to investigate whether

OC exposure by itself or in combination

with positional restraint resulted in respiratory compromise that could put individuals at risk for significant injury or

death. The study also examined the

effects of OC spray/positional restraint

on blood pressure and explored whether

the health effects associated with OC

exposure might be influenced by—

● Body weight and size.

● Asthma or other pulmonary disease.

● The use of respiratory inhaler 

medication.

● A history of smoking.

Study subjects

Thirty-seven individuals (training staff

and cadets) from the San Diego Regional

Public Training Institute were recruited

and enrolled as subjects for the study.

Two subjects were excluded at the outset:

One had fractured his ribs and was unable

to adequately perform pulmonary function

testing; the other had a fractured arm

immobilized in a cast, making it impossible to place him in the restraint position. A third subject was excluded after

fainting when his blood was drawn in

the first trial. He had been exposed to

the placebo spray in the sitting position

but was never exposed to OC spray or

restrained at any time.

Overall, 34 subjects (24 men and 10

women) completed the study. The average

age was 31.7 years, with subjects ranging

from 22 to 46 years. The average weight

was 79.1 kilograms (about 174 pounds),

with subjects ranging from 52 to 107 kilograms (approximately 115 to 236 pounds).

Seven subjects were classified as overweight (with a body mass index, or BMI,

of more than 28 kg/m2

), and eight subjects

had a history of smoking, lung disease,

or respiratory inhaler medication use.

Study design

A randomized, crossover, controlled laboratory study on human subjects was performed, comparing the effects of OC spray

and a placebo spray followed by the sitting and restraint positions. The 34 subjects completed 136 separate trials (4

trials per subject) of varying exposure and

position such that each served as his or

her own control. Eight trials were excluded from analysis because the subject

did not adequately inhale when exposed

to OC spray. As a result, 128 separate

trials were analyzed for the purposes of

this study.

For the spirometric and pulmonary function testing data, an additional four trials

were excluded from the testing because

it did not meet American Thoracic
3

R e s e a r c h i n B r i e f 

Society criteria for reproducibility

and variability.2 An additional two trials were excluded from the findings on

arterial blood gas data because venous

rather than arterial blood was sampled; one trial was excluded from the

findings on blood pressure data due to

mechanical instrument error.

Study findings

Sitting position. Researchers found no

evidence that OC spray inhalation and

exposure resulted in any respiratory

compromise in the sitting position.

Statistically, there was no significant

difference in percent of predicted values for FVC (forced vital capacity—

the amount of air that can be expelled

from the lungs after a maximal inspiration) or FEV1 (the amount of air that

a subject can forcibly expel in 1 second during a forced expiration test)

between the OC and placebo groups

at 1.5 and 10 minutes after exposure.

Clinically, values remained within the

normal range at 1.5 and 10 minutes

after OC exposure and inhalation

(see exhibits 1 and 2).

OC spray exposure did not result in

any statistically significant differences

in blood oxygenation when compared

with placebo in the sitting position.

Blood oxygenation remained at clinically normal levels (see exhibit 3) and

carbon dioxide levels decreased after

exposure to OC spray. This small but

significant finding suggests that ventilation actually increased after OC exposure (see exhibit 4).

Restraint position. The findings of

this study concerning the restraint

position are consistent with the authors’

previous studies on respiratory function and restraint, which found that

restraint led to declines in FVC and

FEV1 but found no evidence of hypoxemia (low levels of blood oxygenation),

hypercapnia (increased carbon dioxide

levels), or hypoventilation (decreased

ventilation of the lungs).3

In this study, researchers found no

evidence that OC exposure resulted

in any additional change in respiratory function in the restraint position.

In both the OC and placebo groups,

pulmonary function was restricted in

the restraint position, but measurements remained within the normal

range. Moreover, there were no statistical differences between the OC

and placebo groups relative to these

declines (see exhibits 1 and 2).

0

20

40

60

80

100

120

Mean % predicted FEV1

Baseline 1.5 minutes 10 minutes

Placebo/sitting OC/sitting

Placebo/restraint OC/restraint

Exhibit 2. FEV1 by exposure and position

Baseline 1.5 minutes 10 minutes

Placebo/sitting OC/sitting

Placebo/restraint OC/restraint

0

20

40

60

80

100

120

Mean % predicted FVC

Exhibit 1. FVC by exposure and position
4

R e s e a r c h i n B r i e f 

Just as in the sitting position, there

was no difference in oxygenation in

the restraint position between the

OC and placebo groups (see exhibit 3).

There was also no difference in carbon

dioxide levels between the two groups

in the restraint position, suggesting

that OC exposure had no adverse effect

on ventilatory function in restrained

subjects (see exhibit 4). Thus, OC inhafor all groups (regardless of exposure

or position) remained well within normal limits (see exhibit 5).

Mean arterial blood pressure, however,

was significantly elevated after exposure to OC spray when compared to

placebo in both the sitting and restraint

positions. This difference, though small,

persisted at 3, 6, and 9 minutes after

exposure (see exhibit 6). The reasons

for this remain uncertain and may simply be related to the discomfort and

pain associated with OC exposure.

Effects of body size and weight.

Researchers found no evidence of

additional restrictive pulmonary dysfunction in seven overweight subjects

in the sitting or even the restraint position with OC or placebo exposure. In

this group, OC exposure did not lead

to hypoxemia or hypoventilation in

either the sitting or restraint position

and actually seemed to improve oxygenation in the sitting position. Clearly,

however, these conclusions must be

tempered by the small size of this subgroup and the fact that none of the

subjects were morbidly obese (BMI

greater than 32 kg/m2

).

Asthma, smoking, respiratory inhaler

medication use. Researchers found no

evidence that OC spray inhalation and

exposure resulted in respiratory compromise in subjects with a history of

lung disease, asthma, smoking, or

respiratory inhaler medication use.

In this subgroup, OC exposure had

no effect on pulmonary function in the

sitting or restraint positions. There was

also no evidence of hypoxemia, hypercapnia, or hypoventilation after OC

inhalation for this group in either the

sitting or restraint positions. Yet while

these results suggest that OC exposure

does not result in respiratory dysfunction in those with potential respiratory

lation had no effect on the pulmonary

function changes, oxygenation, or ventilation associated with restraint.

Cardiovascular effects. Exposure to

OC spray resulted in a small increase

in heart rate when compared with placebo. While statistically significant, this

difference is probably of no clinical

importance, since average heart rates

Baseline 5 minutes 1 minute 9 minutes ABG

% Oxygen saturation (pO2 for ABG*)

90

92

94

96

98

100

Placebo/sitting OC/sitting

Placebo/restraint OC/restraint

Exhibit 3. Oxygenation by exposure and position

End tidal CO2 (pCO2 for ABG*)

30

35

40

45

Baseline 5 minutes 1 minute 9 minutes ABG

Placebo/sitting OC/sitting

Placebo/restraint OC/restraint

Exhibit 4. Ventilation (CO2 levels) by exposure and position

* Arterial blood gas.

* Arterial blood gas.
5

R e s e a r c h i n B r i e f 

abnormalities, it is important to note

that this study cannot make definitive

conclusions due to the small number

of subjects (eight) in this subgroup.

Study caveats and implications

Limitations of this study. This study

was performed on human subjects in a

clinical laboratory and did not attempt

to replicate all the conditions that may

be encountered in the field. Field subjects are often in a state of extreme

agitation and “excited delirium” as a

result of underlying psychiatric disease or intoxication from recreational

drugs. Subjects are often involved in

violent physical struggles before, during, and after the use of OC spray or

positional restraint. There has been

speculation that subjects in the field

undergo extreme levels of exertion

leading to exhaustion that may affect

pulmonary function. Although previous studies have attempted to replicate

exertion and struggle, it is unlikely that

all conditions that occur in the field—

particularly the physiological and psychological effects of stress and trauma—

can be reproduced in the laboratory.

Moreover, as this study focused on

inhalation exposure, all subjects wore

goggles to reduce OC exposure to the

eyes, which causes irritation and pain.

Ocular OC exposure may exacerbate

the physiological stress of field subjects but was not assessed in this study.

In addition, restrained subjects were

placed on a medical examination table

rather than on a hard surface, as often

occurs in field settings.

This study attempted to replicate OC

exposure in the field as much as possible in the laboratory setting. In doing

so, exact capsaicin dosing was not standardized. Rather, subjects, whose heads

were placed in a 5' x 3' x 5' exposure

box, received a standard 1-second spray

directed from 5 feet away as dictated

by both manufacturer recommendations and local police policies regarding the use of OC. Spraying from less

than 5 feet away does not allow for

adequate aerosolization of OC and is

likely to reduce the amount of inhalation exposure.

Exposure in the box was limited to

5 seconds while in the laboratory.

Although this may seem to be a short

period of time, spray in the field usually occurs in an open setting where

OC dissipates rapidly. Moreover, by

containing the spray within the exposure box, it is likely that subjects

were exposed to a much higher

Baseline 5 minutes 1 minute 9 minutes

Heart rate (beats per minute)

60

65

70

75

80

Placebo/sitting OC/sitting

Placebo/restraint OC/restraint

Exhibit 5. Heart rate by exposure and position

Baseline 6 minutes 3 minutes 9 minutes

Mean arterial pressure (MAP) (mmHg)

95

100

105

110

115

120

Placebo/sitting OC/sitting

Placebo/restraint OC/restraint

Exhibit 6. Blood pressure by exposure and position

* Arterial blood gas

* Arterial blood gas
6

R e s e a r c h i n B r i e f 

concentration of capsaicin than might

occur in the open air.

This study did not examine repeated

OC spray exposures, which commonly

occur in the field setting. Researchers

used an aerosol form of OC spray, rather

than the liquid or foam forms that are

also used by law enforcement agencies,

because the aerosol form was more

likely to be inhaled than other forms

and was thus more appropriate for a

study on the respiratory effects of OC.

Although subjects were monitored

carefully for 1 hour after each trial and

were checked by the research staff for

significant adverse reactions, they were

not assessed for any delayed or longterm effects from exposure. Moreover,

this study did not address issues regarding the potential for long-term complications from chronic occupational

exposure to OC.

Finally, it is important to emphasize

the limited nature of the additional

analyses performed on the subgroups

of subjects who were overweight or

had potential respiratory abnormalities. These groups were small in number and the analysis in this study

lacked sufficient statistical power to

make any definite conclusive findings. 

Law enforcement implications. Study

findings support the contention that

OC spray inhalation, even when combined with positional restraint, poses

no significant risk to subjects in terms

of respiratory and pulmonary function.

Although capsaicin spray has been

studied extensively, this study assessed

pulmonary and respiratory function

after exposure to a commercially available OC spray used by law enforcement

agencies nationwide. OC exposure produced no evidence of pulmonary dysfunction, hypoxemia, or hypoventilation

in either the sitting or restraint positions. These findings also applied to the

groups of overweight subjects and to

those with potential respiratory abnormalities. On the issue of in-custody

deaths, this study indicates that OC

inhalation and exposure do not cause

significant respiratory injury and

should not lead to an increased risk

of respiratory compromise, arrest, or

death—thus lending credence to the

large retrospective field studies that

have found little evidence that OC

causes significant respiratory injury.

These findings will aid law enforcement

agencies by providing data supporting

the safety of OC spray, even when used

in combination with positional restraint.

First, they will provide law enforcement

personnel some measure of comfort in

the knowledge that they are employing

force methods that have been tested

and found safe in humans in clinical

rterial blood gas (ABG) test:

A test that analyzes arterial blood for

oxygen, carbon dioxide, and pH. It

is used to test the effectiveness of 

respiration.

Body mass index (BMI): One’s weight

(in kilograms) divided by the square of

one’s height (in meters).

End-tidal CO2: The partial pressure

or maximal concentration of carbon

dioxide (CO2) at the end of an

exhaled breath.

Forced expiratory volume in 1 second (FEV1): The amount of air that a

subject can forcibly expel in 1 second

during a forced expiration test.

Forced vital capacity (FVC): The

amount of air that can be expelled from

the lungs after a maximal inspiration.

Hypercapnia: The presence of excessive

amounts of carbon dioxide in the blood.

Hypoventilation: Decreased ventilation

of the lungs.

Hypoxemia: Deficient oxygenation of

the blood.

Mean arterial blood pressure (MAP):

The average value for arterial blood

pressure (systolic pressure plus diastolic

pressure divided by 2).

Percent of predicted values: Comparison of a specific person’s lung volumes

(the amount of air that can be moved

in and out with each breath and the

amount of air that remains in the lungs)

to values that are normal for that person’s body size, gender, and ethnicity.

pO2: The concentration of oxygen in

arterial blood.

Positional asphyxia: Death caused

by obstructed airways or other interference with breathing resulting from

body position.

Prone maximal restraint (“hogtie”

or “hobble”) position: A position in

which subjects are made to lie prone

with wrists and ankles bound together

behind the back.

Pulmonary function test: Tests

designed to gauge how the lungs are

carrying out their tasks—of expanding

and contracting (when a person inhales

and exhales) and of exchanging oxygen

and carbon dioxide efficiently between

the air (or other gases) within the lungs

and the blood.

A Glossary of Medical Terms
7

R e s e a r c h i n B r i e f 

studies. They may improve the relationship between local agencies and

their communities, as the general

public will be aware that officers in their

communities are employing force methods that have been rigorously studied

in a clinical laboratory on human subjects. Questions regarding OC use in

cases of custody death will be less

likely to contribute to the public controversy and contentiousness that

often follow these cases.

Second, this study will aid law enforcement agencies when facing accusations

of excessive force based on the unfounded contention that OC exposure results

in respiratory compromise. Study data

will assist law enforcement agencies

in deterring and defending themselves

from litigation that can have a negative

impact on the well-being and morale

of their agencies, and, more directly,

on their personnel and field officers.

Third, on a general public policy level,

this study provides solid scientific evidence that can be used in the search

for safer methods of restraint. In the

past, controversy regarding police force

methods and restraint has been based

on anecdotal evidence and case reports,

rather than the scientific study of human

physiology. While many other controversies remain, such as the impact of

physiological and psychological stress,

external weight compression during

restraint, and the cardiovascular effects

of stress and restraint, this study provides a physiological and scientific

basis from which to investigate and

assess law enforcement force methods

and custody restraint procedures.

Notes

1. Granfield, J., J. Onnen, and C.S. Petty,

“Pepper Spray and In-Custody Deaths,”

Executive Brief: Science and Technology,

International Association of Chiefs of Police

and National Institute of Justice, March 1994;

Bunting, S., “First Death Attributed to OC

Occurs in North Carolina,” ASLET Journal 13

(1993): 13; Steffee, C.H., P.E. Lantz, L.M.

Flannagan, R.L. Thompson, and D.R. Jason,

“Oleoresin Capsicum (Pepper) Spray and InCustody Deaths,” American Journal of Forensic

Medicine and Pathology 16 (3) (1995): 185.

Flannagan, L.M., Autopsy Report of the Angelo

Robinson Death, Office of the Chief Medical

Examiner, Chapel Hill, NC, 1993: 1:6.

2. American Thoracic Society, “Standardization

of Spirometry: 1994 Update,” American Journal

of Respiratory and Critical Care Medicine 152

(September 1995): 1107.

3. Chan, T.C., G.M. Vilke, T. Neuman, and

J.L. Clausen, “Restraint Position and Positional

Asphyxia,” Annals of Emergency Medicine 30

(1997): 578.

Theodore C. Chan, M.D., is assistant

clinical professor of medicine in the

Department of Emergency Medicine

at the University of California, San

Diego School of Medicine and

Medical Center.

Gary M. Vilke, M.D., is assistant 

clinical professor of medicine in the

Department of Emergency Medicine

at the University of California, San

Diego School of Medicine and

Medical Center.

Jack Clausen, M.D., is professor of

medicine in the Division of Pulmonary

Medicine of the Department of Internal

Medicine at the University of California,

San Diego School of Medicine and

Medical Center and the director of

its Pulmonary Function Laboratory.

Richard Clark, M.D., is professor of

clinical medicine in the Department of

Emergency Medicine and the Division

of Medical Toxicology at the University

of California, San Diego School of

Medicine and Medical Center and

medical director of the California

Poison Control System–San Diego

Division.

Paul Schmidt, M.S., is supervising

academy instructor for the San Diego

City Police Department and first aid

and physical fitness core instructor for

the San Diego Regional Public Safety

Training Institute.

Thomas Snowden is a deputy sheriff

in San Diego County and defensive tactics core instructor for the San Diego

Regional Public Safety Training

Institute.

Tom Neuman, M.D., is professor of

clinical medicine in the Departments

of Pulmonary Medicine and Internal

Medicine at the University of California,

San Diego School of Medicine and

Medical Center.

This study was supported by

98–IJ–CX–0079 awarded to the

University of California, San Diego

by the National Institute of Justice.

Findings and conclusions of the research

reported here are those of the authors and do

not necessarily reflect the official position or

policies of 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.

NCJ 188069

This and other NIJ publications can be

found at and downloaded from the NIJ

Web site (http://www.ojp.usdoj.gov/nij).
U.S. Department of Justice

Office of Justice Programs

National Institute of Justice

Washington, DC 20531

For Further Reading

Chan, T.C.; Vilke, G.M.; Clausen, J.; Clark, R.F; Schmidt, P; Snowden, T.; Neuman, T.; “The Effect of Oleoresin Capsicum ‘Pepper’

Spray Inhalation on Respiratory Function, “ in the Journal of Forensic Science, 2001, 47(2). In press.

Kaminski, R.J.; Edwards, S.M.; Johnson, J.W. (1999) “Assessing the Incapacitative Effects of Pepper Spray during Resistive

Encounters with the Police.” Policing: An International Journal of Police Strategies and Management, 22 (1):7–29.

Kaminski, R.J.; Edwards, S.M..; Johnson, J.W., (1998) “The Deterrent Effects of Oleoresin Capsicum on Assaults Against police:

Testing the Velcro-Effect Hypothesis.” Police Quarterly, 1(2): 1-20. 

An NIJ Science and Technology Update, forthcoming 2002, will contain summaries of two NIJ-funded studies of the effects of OC

spray: Bowling, J.M., and Gaines, M, “An Evaluation of Oleoresin Capsicum (OC) Use by Law Enforcement Agencies: Impact on

Injuries to Officers and Suspects,” and Petty, C.S., “Deaths in Police Confrontation When Oleoresin Capsicum Is Used.”