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One week ago Tuesday, a confrontation led to St. Paul police using chemical irritants and projectiles on a crowd. Hundreds of people gathered to protest and document the arrest of two people by federal immigration agents. The police department says it is reviewing officers’ response.  

The incident came just days after a similar confrontation with federal agents in another part of the city. They, too, used chemical irritants and projectiles.  

In cities across the country, federal immigration actions have resulted in frequent clashes between law enforcement and community members who are organizing to respond. More could be on the horizon after 

 that federal agents are expected to target hundreds of Somali immigrants in the Twin Cities. Minneapolis and St. Paul leaders said in a press conference that local law enforcement will not assist the operation but will respond to public safety threats. 

To understand more about the health impacts of what are called less lethal methods of crowd control, MPR News host Nina Moini talked with Dr. Rohini Haar. She is an emergency physician, a medical advisor for the group Physicians for Human Rights and a lecturer in the University of California-Berkeley law school.

The conversation below has been edited for length and clarity. 

What are chemical irritants and how are they deployed?

Chemical irritants is a really broad category, but the main two weapons that we see being used are what we call tear gases [and pepper]. Usually [tear gas] is a powder that is in canisters or tear gas grenades, and when the canister explodes, it sort of aerosolizes the powder. 

The second group is the pepper, like pepper spray and its synthetic version called PAVA. They can be powderized but also in an oil base. That's what you often see in pepper spray, but also in canisters, or more frequently, in what they're calling pepper balls, which are small projectiles that explode when they hit a person and spray this chemical irritant on them.

What are some of the short-term health impacts of tear gas and pepper spray?

The short-term impacts are the intended ones. They say they're for pain compliance, or to cause pain so that people comply with authorities. Tearing, of course, of the eye, but also spasms of the eyelid, because it causes burning pain, a lot of burning and pain on their skin. 

And then the most scary ones are probably the respiratory, so feeling like you're coughing or suffocating or can't breathe, can't catch a breath. 

Even though these weapons have been around for more than 100 years, they're not very well studied, and certainly manufacturers don't share data on their safety. So there's known health effects in terms of potentially all kinds of different parts of the body. There's people who have died from the canister injuries themselves. There's blindness and then a lot of allergic reactions when you're exposed repeatedly.

Even single exposures can have significant harm. Chemical burns, eye injuries and respiratory harm, burning of your bronchia, are some of the things I've seen in case reports. And those canisters and pepper balls, they act effectively as projectiles, as bullets. Those can cause a lot of blunt trauma as well, even in a single exposure.

Would you say there's sufficient information out there for you to be comfortable with law enforcement deploying these methods?

I think law enforcement needs to be more transparent about both what is used, in terms of what's the concentration inside these canisters, what weapon is actually being used — protesters often don't know — but also about how much is being used and when it's being used. Is it justified? Is it proportionate? Is precaution being taken to protect innocent bystanders and to limit harm?

What laws, if any, govern how law enforcement use these methods?

The Chemical Weapons Convention [in international law] bans the use of all of these agents as riot control agents by the military or in war. But it does have an exception for police use in civilian policing. The U.S., our police usually have guidelines on proportionality and use of force and being careful when using them. These are often not used by the federal agents that you're describing and you can see the trends and patterns are quite different.

In California, we have a law that both demands that you share how many of these weapons you are holding in your arsenal, as well as how many are fired. That kind of thing is really helpful in the long-term to understand what the use looks like. Filing incident reports is also another really helpful thing, so we can understand what's used, how much and when, when people get harmed.

What should people know ahead of time if there's a chance that they will be exposed to tear gas or pepper spray?

The number one thing we advise is to just care for yourself and make sure you're okay first before doing anything else, if you're exposed. Decontamination, getting out of that space with the chemical irritant, and then taking off any contaminated clothes or items is probably the top things. Fresh air and water, and then rinsing with soap and water is really important. 

The other thing I would say is, the reason we know so much about what's going on is because people are videoing and putting that up on different media. I think it's important to continue documenting what's going on across the United States.

Use the audio player above to listen to the full conversation.

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Dr. Rohini Haar is a California-based emergency physician and human rights expert who has studied the health effects of less-lethal methods.

In two recent immigration enforcement actions in St. Paul, federal law enforcement and city police used chemical irritants to control crowds. Dr. Rohini Haar is a California-based emergency physician and human rights expert who studies the health impacts of these methods. 

How pepper spray and tear gas used by law enforcement impact human health

A man moves through a cloud of chemicals.

How pepper spray and tear gas used by law enforcement impact human health

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