M25A2 CS1 Riot Grenade

Overview

The M25A2 CS1 Riot Control Grenade is a hand-thrown pyrotechnic device designed to disperse o-chlorobenzylidene malononitrile (CS) tear gas for riot control, crowd dispersal, and non-lethal tactical operations. As a specialized riot control munition, the M25A2 produces a dense cloud of CS irritant agent that causes intense tearing, respiratory irritation, and skin burning sensations, temporarily incapacitating individuals within the affected area without causing permanent injury. The M25A2 represents the U.S. military’s standard hand-deployed CS grenade and has been widely used in military police operations, civil disturbance control, and training exercises since its adoption in the 1960s.

Country/Bloc of Origin

  • Country: United States
  • Development Period: 1960s
  • International Use: Widely adopted by U.S. military, law enforcement agencies, and supplied to allied nations
  • Licensed Production: Manufactured by multiple U.S. defense contractors
  • Current Status: Active in U.S. military and law enforcement inventories, though usage is regulated by strict rules of engagement

Ordnance Class

  • Type: Hand grenade (riot control agent)
  • Primary Role: Riot control and crowd dispersal
  • Secondary Role: Area denial, training (chemical agent familiarization)
  • Delivery Method: Hand-thrown pyrotechnic device
  • Classification: Non-lethal chemical irritant munition (under normal conditions)
  • Agent Type: CS tear gas (lachrymatory agent)

Ordnance Family/Nomenclature

  • Primary Designation: M25A2 CS Riot Control Grenade
  • Agent Designation: CS1 (micronized o-chlorobenzylidene malononitrile)
  • NATO Stock Number: 1330-00-073-9815
  • Common Names:
    • “CS Grenade”
    • “Tear Gas Grenade”
    • “Riot Control Grenade”
  • Related Variants:
    • M25 (earlier version, replaced by M25A2)
    • M25A1 (intermediate variant)
    • M7A3 CS Grenade (larger capacity variant)
    • ABC-M25A2 (air-delivered version)
  • Similar Munitions:
    • M651 CS Grenade (tactical CS grenade)
    • CN Grenades (chloroacetophenone agent, largely phased out)

Hazards

While designed as a “non-lethal” munition, the M25A2 presents multiple significant hazards that can cause serious injury or death under certain circumstances:

Primary Hazards:

  • Respiratory Distress: Intense respiratory irritation, coughing, choking sensation
  • Ocular Effects: Severe tearing, temporary blindness, eye pain
  • Skin Irritation: Burning sensation on exposed skin, blistering in sensitive individuals
  • Panic and Disorientation: Psychological effects can cause dangerous panic behavior
  • Asphyxiation Risk: In enclosed spaces or with prolonged exposure, CS can cause respiratory failure

Secondary Hazards:

  • Thermal Burn: Grenade body becomes extremely hot (300-500°F) during functioning
  • Fire Hazard: Burning pyrotechnic composition can ignite flammable materials
  • Trampling/Crush: Panicked crowds fleeing CS exposure can cause stampede injuries
  • Allergic Reactions: Some individuals experience severe allergic responses to CS
  • Cardiovascular Stress: Respiratory distress can trigger cardiac events in vulnerable individuals

High-Risk Populations:

  • Infants and Children: Particularly vulnerable to respiratory effects
  • Elderly: Increased risk of cardiac and respiratory complications
  • Asthmatics: CS can trigger severe asthma attacks
  • Individuals with Heart Conditions: Stress response can trigger cardiac events
  • Pregnant Women: Potential risk to fetus from respiratory distress

Danger Zones:

  • Immediate Danger Zone: 10 meters radius (direct exposure, thermal hazard)
  • Effective Agent Zone: 20-30 meter radius in still air
  • Downwind Hazard: CS cloud can travel 100+ meters downwind
  • Enclosed Space: Extreme danger – CS concentration can be lethal

Fatal Exposure Scenarios:

  • Deployment in enclosed spaces without ventilation
  • Prolonged exposure (>30 minutes) in concentrated cloud
  • Multiple grenades in confined area
  • Deployment against immobilized individuals unable to escape
  • Use against individuals with severe respiratory conditions

Key Identification Features

Physical Dimensions:

  • Length: 5.5 inches (140 mm)
  • Diameter: 2.4 inches (61 mm)
  • Weight: 13.5 ounces (383 grams) filled
  • CS Agent Weight: 3.5 ounces (95 grams)

External Appearance:

  • Body Material: Sheet steel canister with rolled seam construction
  • Body Color: Gray body with single red band around circumference
  • Markings: “CS M25A2” or “RIOT CS M25A2” stenciled in black
  • Top Assembly: M201A1 fuze with pull ring and safety lever
  • Bottom: Four emission holes (0.5 inch diameter) for gas dispersal

Distinctive Features:

  • Color Coding: Red band indicates riot control agent (per U.S. military color code)
  • Emission Holes: Four large holes at base distinguish from smoke grenades
  • Safety Assembly: Standard spoon-type lever with pull pin and clip
  • Text Markings: “CS” clearly marked to distinguish from other chemical agents
  • Lot Number: Manufacturing lot and date code stamped on body

Material Composition:

  • Steel canister body
  • Pyrotechnic composition (burns to disperse CS)
  • CS1 agent (micronized crystalline powder)
  • M201A1 pyrotechnic delay fuze
  • Steel safety lever and pull pin

Distinguishing from Similar Grenades:

  • Red band (vs. purple for WP, green for colored smoke, light green for HC)
  • Four emission holes at base (vs. closed bottom on fragmentation grenades)
  • “CS” marking clearly visible
  • Slightly smaller and lighter than M34 WP smoke grenade

Fuzing Mechanisms

Fuze Type:

The M25A2 employs the M201A1 pyrotechnic delay fuze, designed specifically for riot control and smoke munitions requiring continuous emission.

Arming Sequence:

  1. Safe State: Safety lever held against body by pull pin and safety clip
  2. Pin Removal: User removes safety pin while firmly gripping safety lever
  3. Lever Release: Upon throwing, spring-loaded striker is released
  4. Striker Impact: Striker hits percussion primer, initiating fuze delay
  5. Delay Burn: 1-2 second pyrotechnic delay burns down
  6. Igniter Function: Delay column ignites main pyrotechnic composition
  7. Agent Emission: Pyrotechnic heat vaporizes and disperses CS agent through emission holes
  8. Continuous Burn: Grenade emits CS-laden smoke for 15-35 seconds

Key Timing:

  • Fuze Delay: 1-2 seconds from lever release to emission start
  • Emission Duration: 15-35 seconds of continuous CS dispersal
  • Peak Concentration: Achieved at 10-15 seconds into emission
  • Residual Effect: CS particles remain airborne for several minutes after emission stops

Safety Features:

  • Pull pin must be removed intentionally (requires 10-15 lbs force)
  • Safety clip provides secondary retention
  • Safety lever prevents accidental striker release
  • Clear “PULL” marking on safety pin ring
  • Requires positive grip and release action to arm

Functioning Mechanism:

Unlike fragmenting grenades, the M25A2 uses a pyrotechnic burner that:

  • Burns at controlled rate to avoid canister rupture
  • Heats CS agent to sublimation point
  • Creates pressure that forces CS vapor through emission holes
  • Maintains emission for full duration of pyrotechnic burn
  • Does not explode or fragment

Anti-Handling:

  • No built-in anti-handling devices
  • UXO is rare but possible if pyrotechnic fails to ignite
  • Partially-functioned grenades may still contain active CS and burning pyrotechnic

History of Development and Use

Development Timeline:

Pre-CS Era (1910s-1950s): Early riot control agents included chlorine gas (WWI), CN (chloroacetophenone), and other lachrymators. These early agents were either too dangerous, too weak, or caused significant injuries. The search for a more effective, safer riot control agent led to research into various compounds during the 1950s.

CS Discovery and Development (1928-1960s): CS (o-chlorobenzylidene malononitrile) was first synthesized by American chemists Ben Corson and Roger Stoughton in 1928 (thus the “CS” designation from their initials). However, it wasn’t until the late 1950s and early 1960s that British researchers discovered CS’s potential as a riot control agent. The compound was found to be significantly more potent than CN while being safer in terms of long-term health effects. The U.S. military quickly recognized CS’s advantages and began developing delivery systems.

M25 Series Introduction (1960s): The M25 series of CS grenades was developed in the early 1960s as the U.S. military’s standard hand-deployed riot control munition. The original M25 was followed by the improved M25A1 and finally the M25A2, which featured better pyrotechnic composition for more consistent emission and improved dispersal patterns.

Vietnam War (1965-1975): The M25A2 saw extensive use during the Vietnam War, though its application was controversial. While designed for riot control, CS grenades were used tactically to clear tunnel systems, bunkers, and fortified positions. The U.S. military also used massive quantities of CS during the war, delivered by various means including hand grenades, grenades launched from helicopters, and bulk powder dispersed from aircraft.

Domestic Use (1960s-1980s): During the civil rights era and anti-war protests of the 1960s and 1970s, M25A2 grenades and similar CS munitions were used by National Guard units and military police during civil disturbances. Notable uses included the 1970 Kent State incident, various prison riots, and urban unrest. This domestic use led to increased scrutiny of CS agents and policies governing their deployment.

Post-Cold War Era (1990s-2000s): The M25A2 continued to serve as the standard riot control grenade through the 1990s. It was deployed during the 1992 Los Angeles riots, various overseas peacekeeping operations (Somalia, Haiti, Balkans), and in military training for chemical defense. Law enforcement agencies also adopted military-surplus M25A2 grenades for tactical situations requiring crowd dispersal.

Modern Era and Controversy (2010s-Present): The 2010s and 2020s saw increased controversy over the use of CS and other riot control agents, particularly during the Ferguson protests (2014), Standing Rock protests (2016), and nationwide protests in 2020. Questions were raised about the safety of CS, especially when used in enclosed spaces, against vulnerable populations, or in excessive quantities. Several jurisdictions banned or restricted the use of CS grenades. The M25A2 remains in military inventory but is subject to strict rules of engagement and legal oversight.

Notable Deployments:

  • Vietnam War: Tactical use for tunnel/bunker clearing
  • Civil Disturbances: Kent State (1970), Los Angeles Riots (1992)
  • Prison Riots: Attica (1971), numerous others
  • Military Operations: Waco siege (1993), though primary agent was different
  • Overseas Peacekeeping: Somalia, Haiti, Balkans
  • Training: Routine use in gas chamber training for military personnel
  • Recent Protests: Ferguson (2014), nationwide protests (2020)

Legal and Policy Evolution:

The use of CS and the M25A2 has been shaped by international law, particularly the Chemical Weapons Convention (CWC) of 1993, which permits the use of riot control agents for domestic law enforcement but prohibits their use as “a method of warfare.” This creates a complex legal framework where the M25A2 can be used by military police for base security or by deployed forces for riot control, but cannot be used as a tactical weapon against enemy combatants during warfare.

Technical Specifications

Chemical Agent:

  • Agent Type: CS1 (o-chlorobenzylidene malononitrile)
  • Agent Form: Micronized crystalline powder
  • Agent Weight: 3.5 ounces (95 grams)
  • Agent Purity: 95%+ CS
  • Chemical Formula: C₁₀H₅ClN₂
  • Molecular Weight: 188.6 g/mol

Pyrotechnic Composition:

  • Burner Type: Slow-burning pyrotechnic mix (composition classified)
  • Burn Rate: Designed to emit CS over 15-35 seconds
  • Burn Temperature: 300-500°F (150-260°C)
  • Ignition System: M201A1 percussion-initiated delay fuze

CS Agent Effects:

  • Onset Time: Immediate upon exposure (5-20 seconds)
  • Peak Effects: 1-3 minutes after exposure
  • Clearance Time: 15-30 minutes after leaving contaminated area
  • Persistence: CS particles remain in air 5-10 minutes; on surfaces 1-2 hours

Agent Concentration and Coverage:

  • Effective Concentration: 1-5 mg/m³ causes incapacitation
  • Lethal Concentration (LCt₅₀): 61,000 mg·min/m³ (extremely high, requiring prolonged enclosed space exposure)
  • Coverage Area: 20-30 meter radius in still air
  • Wind Effect: Significant – cloud extends 100+ meters downwind

Emission Characteristics:

  • Emission Method: Pyrotechnic vaporization through four base holes
  • Emission Duration: 15-35 seconds continuous
  • Emission Rate: Peak at 10-15 seconds
  • Cloud Height: Rises 10-15 feet due to thermal convection

Performance Factors:

  • Temperature Sensitivity: Operates -40°F to +140°F (-40°C to +60°C)
  • Humidity Effect: High humidity increases CS effectiveness (agent absorbs moisture)
  • Wind Sensitivity: Highly susceptible – strong winds rapidly disperse agent
  • Enclosed Space: Extreme danger – concentration can reach lethal levels

Storage and Shelf Life:

  • Storage Temperature: 40-80°F (4-27°C) recommended
  • Shelf Life: 10-15 years under proper storage
  • Humidity Control: Must be kept dry; CS degrades in moisture
  • Inspection Frequency: Annual inspection for corrosion/leakage

Deployment Considerations:

  • Minimum Safe Distance: 10 meters from friendly forces without protective masks
  • Protective Equipment Required: M40 gas mask or equivalent for operating personnel
  • Decontamination: Ventilation, water wash for personnel, CS powder brushed off surfaces
  • Neutralization: Dilute bleach solution (5% sodium hypochlorite) neutralizes CS on surfaces

Frequently Asked Questions

Q: How does CS tear gas affect the human body, and why is it effective for riot control?

A: CS (o-chlorobenzylidene malononitrile) is a lachrymatory agent that acts as a potent sensory irritant. Upon exposure, CS particles come into contact with moisture on the eyes, respiratory tract, and skin. The chemical reacts with this moisture to form a weak acid that activates pain receptors (TRPA1 receptors) throughout the exposed tissues. In the eyes, this causes immediate, intense tearing, burning pain, involuntary eye closure, and temporary blindness. In the respiratory system, CS causes coughing, choking sensations, chest tightness, and difficulty breathing. On the skin, particularly in moist areas (armpits, groin), CS causes intense burning sensations. The effects are so uncomfortable that most individuals will immediately attempt to flee the affected area, making CS highly effective for crowd dispersal. The key to CS’s utility as a riot control agent is that while the effects are intense and debilitating, they are temporary – most symptoms resolve within 15-30 minutes after leaving the contaminated area, with no permanent damage under normal exposure conditions.

Q: Can CS tear gas be lethal, and under what circumstances does it become dangerous?

A: While CS is designed to be “non-lethal,” it can indeed be lethal under certain circumstances, though deaths are rare. The lethal concentration (LCt₅₀) for CS is extremely high – approximately 61,000 mg·min/m³ – which is difficult to achieve in open air. However, fatalities have occurred in situations where: (1) multiple grenades were used in enclosed spaces, creating dangerously high concentrations; (2) individuals were trapped or restrained and unable to escape the CS cloud; (3) vulnerable populations (infants, elderly, asthmatics) were exposed; (4) individuals had pre-existing cardiac or respiratory conditions that were exacerbated by the stress response; or (5) prolonged exposure (>30 minutes) occurred in concentrated environments. Deaths attributed to CS typically result from asphyxiation, cardiac arrest triggered by respiratory distress, or secondary effects like trampling during panic. The grenade itself also presents a thermal hazard – the burning pyrotechnic can cause severe burns if someone handles it while functioning, and the grenade body becomes extremely hot (300-500°F).

Q: What’s the difference between the M25A2 CS grenade and the CN grenades it replaced?

A: CN (chloroacetophenone, also known as Mace) was the U.S. military’s primary riot control agent before CS was adopted in the 1960s. The key differences are significant: CS is approximately 10 times more potent than CN, meaning much lower concentrations are needed for effective crowd control. CS has a faster onset – effects begin within seconds versus 20-30 seconds for CN. CS’s effects are more intense but also clear more quickly (15-30 minutes vs. 30-60 minutes for CN). Critically, CS is considered safer than CN – while both are irritants, CN is more likely to cause skin blistering, eye damage, and respiratory injuries with prolonged exposure. CN is also more persistent in the environment. These advantages led to CS completely replacing CN in U.S. military inventory by the 1970s. The M25A2 CS grenade offers better dispersal characteristics and more reliable pyrotechnic functioning than the older CN grenades it replaced, while delivering a more potent but paradoxically safer (in terms of permanent injury) riot control effect.

Q: Why does the M25A2 have holes in the bottom rather than dispersing agent from the top like smoke grenades?

A: The M25A2’s design with four emission holes at the base is intentional and serves several important purposes. First, the bottom-emission design creates better ground-level coverage of the CS agent. Since the pyrotechnic burner heats the CS and creates upward air currents, having emission holes at the bottom ensures that CS vapor is distributed from ground level upward, creating a dense cloud that affects individuals standing on the ground – exactly where rioters would be. If emission were from the top, the CS-laden smoke would tend to rise quickly and disperse at higher elevations, missing the target population. Second, the bottom holes allow the grenade to function effectively even when it lands on its side or rolls after impact, whereas top emission would be less effective in these positions. Third, bottom emission means the hot grenade body is elevated off the ground contact point, reducing the risk of the pyrotechnic igniting flammable materials it lands on. Finally, this design creates a more predictable emission pattern – the CS cloud builds from the grenade location outward and upward in a relatively uniform pattern, making it easier for operators to predict coverage and avoid friendly-fire contamination.

Q: Is CS tear gas banned by international law, and why is it legal for riot control but not warfare?

A: The legal status of CS is complex and often misunderstood. The 1993 Chemical Weapons Convention (CWC), which the United States and 193 other nations have ratified, explicitly prohibits the use of riot control agents (including CS) “as a method of warfare.” This means military forces cannot use CS grenades like the M25A2 against enemy combatants during armed conflict. However, the same treaty explicitly permits the use of riot control agents for “law enforcement including domestic riot control purposes.” This creates a paradox: CS can be used by military police to control riots at a military base or by civilian law enforcement to disperse crowds, but cannot be used by combat troops against enemy forces even in scenarios where less-lethal options might save lives. The reasoning behind this distinction is the concern that allowing any chemical weapons in warfare could lead to escalation to more dangerous chemical agents, and the difficulty of distinguishing between “riot control” use and tactical chemical warfare on a battlefield. Some human rights organizations have called for broader restrictions on CS use, arguing that even in law enforcement contexts, the agent can cause serious injuries and deaths, particularly when used improperly.

Q: What protective equipment is needed when deploying M25A2 grenades, and what decontamination procedures should be followed?

A: Personnel deploying M25A2 grenades must use appropriate protective equipment to avoid self-contamination, as the CS cloud can easily drift back toward the operators depending on wind conditions. At minimum, operators should wear: a properly fitted M40 or M50 series protective mask (or equivalent civilian gas mask with appropriate filters); long sleeves and gloves to minimize skin exposure; and eye protection integrated into the mask. For sustained operations or in enclosed areas, full MOPP (Mission Oriented Protective Posture) gear may be required, including overgarments and boots. After deployment, personnel and equipment will likely be contaminated with CS residue. Decontamination procedures include: immediately moving to an uncontaminated area upwind; removing the protective mask only after ensuring the area is clear; removing outer garments and allowing them to air out (CS will sublimate over time); washing exposed skin with large amounts of water and soap (do not use hot water initially, as it opens pores and can worsen effects); flushing eyes with clean water or saline for several minutes; and washing contaminated equipment with soapy water or dilute bleach solution (5% sodium hypochlorite). Personnel should face into the wind with eyes open during initial decontamination to help ventilate CS from the face and eyes. Contaminated clothing should be washed separately from other laundry.

Q: How does weather affect the performance of the M25A2 grenade?

A: Weather conditions dramatically influence the tactical effectiveness of the M25A2 and all riot control agents. Wind is the most critical factor – in calm conditions, the CS cloud forms a relatively stationary, concentrated area of 20-30 meters radius. Even light winds (5-10 mph) will shift this cloud downwind, potentially contaminating friendly forces or missing the intended target area. Strong winds (15+ mph) rapidly disperse the CS, significantly reducing concentration and effectiveness while extending the hazard area unpredictably. Rain has mixed effects: light rain or high humidity actually enhances CS effectiveness because the moisture helps CS particles adhere to exposed skin and respiratory passages, intensifying the irritant effects. However, heavy rain physically washes CS particles out of the air and dilutes the agent, reducing effectiveness. Temperature affects both the grenade’s functioning and the agent’s behavior – in very cold conditions (below 20°F), the pyrotechnic may burn less efficiently and CS sublimation is reduced. In hot conditions, CS vaporizes more readily but may also disperse faster. Operators must account for these factors when deploying CS grenades, including predicting wind drift, positioning upwind of the target, and adjusting the number of grenades based on conditions.

Q: What are the long-term health effects of CS exposure, and is it safe for repeated use in training?

A: The long-term health effects of CS exposure remain somewhat controversial. Most medical research indicates that brief, acute exposure to CS (such as experienced during a single riot control event or military gas chamber training) does not cause permanent injury to healthy individuals. The standard military training exposure involves entering a gas chamber filled with CS for 30-60 seconds, which causes intense but temporary effects that resolve within 15-30 minutes. However, concerns exist about: (1) repeated exposures – military personnel, law enforcement, and individuals living in areas where CS is frequently deployed may experience cumulative effects; (2) respiratory sensitization – some studies suggest repeated CS exposure may worsen asthma or cause long-term respiratory symptoms in some individuals; (3) skin sensitization – allergic dermatitis has been reported after repeated exposures; (4) psychological effects – the intense discomfort of CS can cause lasting anxiety about chemical agents. Some research has indicated possible carcinogenic effects in animal studies, though human evidence is limited. The U.S. military considers CS safe for training use and continues to use it in gas chamber exercises for all personnel. However, trainees with severe asthma, respiratory conditions, or skin sensitivities may be medically exempted from CS training. The consensus is that occasional exposure in controlled circumstances carries minimal long-term risk, but the effects of frequent, high-concentration, or prolonged exposure are less well understood.

Q: Can the M25A2 be used safely indoors, and what happened in past incidents where CS was used in buildings?

A: Using the M25A2 or any CS grenade indoors is extremely dangerous and has led to numerous deaths and serious injuries. When deployed in enclosed spaces, CS cannot dissipate and instead builds to dangerous concentrations. Even a single M25A2 grenade in a small room can create CS concentrations that cause severe respiratory distress, asphyxiation, and potentially death, especially if individuals cannot escape. Historical incidents include: the 1993 Waco siege, where CS was pumped into the Branch Davidian compound (though a different delivery system was used, the enclosed space concentration was a key factor in the tragedy); numerous prison riots where CS grenades used in confined spaces led to inmate deaths; and tactical operations where SWAT teams deployed CS in buildings, resulting in suspect or officer injuries. The fundamental problem is that while CS is designed for outdoor crowd dispersal where people can flee to fresh air, enclosed spaces trap both the CS and the exposed individuals. Current U.S. military and law enforcement doctrine strictly limits indoor CS use and requires special authorization, extensive safety protocols, and usually alternatives like smaller, controlled-delivery systems. If CS must be used indoors, the minimum requirements include: evacuation routes for all individuals; adequate ventilation; medical personnel on standby; and use of minimum quantities. Even with precautions, indoor CS deployment carries significant legal and medical risks.

SAFETY WARNING: The M25A2 CS Riot Control Grenade is a chemical munition that can cause serious injury or death under certain circumstances. While designed as a “non-lethal” option, CS tear gas is dangerous, especially for vulnerable populations, in enclosed spaces, or with prolonged exposure. This information is provided for educational purposes only. Civilians should never handle, deploy, or attempt to neutralize CS grenades. If you encounter a suspected M25A2 or similar chemical munition, evacuate the area and contact law enforcement or military authorities. Chemical agents require specialized training and protective equipment for safe handling.