BM-21 Grad Unexploded Rocket Clearance in Surin Province: EOD Assessment of Deep-Buried ERW in Agricultural Terrain

Technical Summary

Thai Explosive Ordnance Disposal (EOD) teams are conducting a systematic Explosive Remnants of War (ERW) clearance operation across agricultural land in Surin province, northeastern Thailand, following the 2025 Cambodian–Thai border conflict. Reporting from 8 May 2026 confirms that 189 BM-21 Grad 122 mm rockets have been identified and catalogued in Kap Choeng district alone, with a further estimated 400–500 rocket impact sites in adjacent Phanom Dong Rak district. Total rounds fired by Cambodian forces is reported at approximately 700 BM-21 rockets across 98 aim points in four northeastern Thai provinces. Clearance has been requested by local farmers ahead of the monsoon planting season.

The BM-21 Grad is a Soviet-designed 40-round 122 mm multiple launch rocket system (MLRS) with a range of approximately 20–40 km depending on rocket variant. The standard munition assessed for the Cambodian inventory on this system is the 9M22 series: a 66 kg High Explosive–Fragmentation (HE-FRAG) rocket fitted with a point-detonating or graze-sensitive fuze. Under normal operating conditions, dud rates for 9M22-series rockets are estimated at 3–8% of rounds fired, varying with fuze lot age, storage condition, and angle-of-impact geometry. Applied to the approximately 700 rounds reported fired, this gives a predicted ERW population of 21–56 items; however, observed counts substantially exceed the upper estimate, suggesting a higher in-service dud rate consistent with aged or poorly maintained ammunition stocks.

Analysis of Effects

The principal EOD challenge in this clearance task is vertical penetration depth in saturated soil. Surin EOD commanders have reported rocket penetration to depths exceeding 10 metres in rain-soaked agricultural ground, with theoretical penetration depths of up to 20 metres cited in highly saturated, low-density alluvial soils. At these depths, standard surface-sweep metal detection is rendered largely ineffective for primary location; geophysical detection methods such as extended-range electromagnetic induction or ground-penetrating radar are required to confirm depth and orientation before excavation commences.

Where rockets have retained their fuze in a mechanically armed state following impact without high-order detonation, the ERW item is assessed as Hazard Division (HD) 1.1 with a Net Explosive Quantity (NEQ) of approximately 6.4 kg TNT equivalent for the warhead fill (assessed as TNT or an equivalent melt-cast composition; specific fill unconfirmed). A high-order detonation at surface level would produce a nominal Lethal Radius (LR) of approximately 150 m and a Casualty Radius (CR) of approximately 300 m in open terrain, per conservative fragmentation modelling consistent with AOP-7 Edition 3. Agricultural personnel working at ploughing or tilling depth (typically 0.2–0.5 m) face a direct initiation risk if a deep-buried item migrates toward the surface through differential soil settlement over successive growing seasons.

The scale of this clearance task — potentially 600 or more confirmed or suspected items across two districts — indicates a protracted operational timeline. Assuming an EOD team productivity rate of 5–10 confirmed-and-disposed items per team per day under field conditions (excavation, render-safe assessment, blow-in-place or removal to demolition ground), full clearance of the known footprint at current resource levels is estimated to require several months of sustained operations before the affected agricultural area can be certified as cleared.

Personnel and Safety Considerations

EOD operators conducting deep excavation tasks face elevated hazard from collapse of poorly consolidated soil walls during mechanical digging and from unplanned initiation during handling of items with degraded fuze components. Standard International Mine Action Standards (IMAS) procedures for deep-buried items require manual excavation within 1 m of the confirmed item location, prohibiting mechanical plant below that proximity threshold. The fuze state of any item that has penetrated to greater than 5 m is not reliably assessable without extraction; render-safe decisions will typically default to blow-in-place (BIP) using a sympathetic detonation charge placed on the excavated item, accepting secondary fragmentation within a cleared exclusion zone sized to the estimated NEQ.

ATOs and EOD practitioners operating in or advising on the region should note that Cambodian BM-21 ammunition stocks, which derive from Chinese and Soviet-era supply chains, may include 9M28F thermobaric and 9M22S incendiary rocket variants alongside the standard HE-FRAG configuration. Visual identification of these variants requires confirmation of warhead colour-coding and lot markings, which may be absent or degraded following deep soil penetration and prolonged burial. Misclassification of a thermobaric or incendiary item as a standard HE round will result in an underestimated Minimum Safe Distance (MSD) and potentially inadequate exclusion-zone sizing for the BIP operation.

Data Gaps

DATA GAP: Exact fuze model fitted to Cambodian BM-21 rounds not confirmed; point-detonating variants with delay element cannot be excluded, materially affecting armed-versus-safe assessment on individual items. DATA GAP: Warhead explosive composition (TNT versus equivalent fill) not publicly confirmed; NEQ estimate carries uncertainty of approximately ±15%. DATA GAP: Proportion of thermobaric or incendiary variants in the fired batch is unknown; total ERW count in Phanom Dong Rak district remains an estimate. DATA GAP: EOD team numbers, nationality of advisers (if any), and current clearance methodology not reported in open source. DATA GAP: Whether any items have been extracted in an armed fuze state has not been disclosed publicly.

AI-assisted technical assessment based on open-source reporting (Khaosod English, May 2026) and open EOD technical references. Not a formal intelligence product. NEQ and fragmentation parameters are indicative only and must not be used as the basis for operational render-safe decisions.