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The area effects of weapons and the risk of civilian harm written by laura boillot

November 2021

Explosive weapons function by exerting powerful forces and projecting blast and fragmentation around a point of explosive detonation.

All explosive weapons will affect an area to some degree. The immediate heat, blast and fragmentation around the point of detonation are always present - to a greater or lesser extent depending on the weapon type. Where explosive weapons are dropped from the air, or fired at a target, this creates additional uncertainties related to ‘accuracy’ or ‘precision’ - so the weapon’s effects may occur somewhere within a wider area. The use of multiple explosive weapons compounds these factors.

The area effects of a weapon have a direct bearing on the likelihood and potential scale of harm to civilians and of damage to civilian objects, such as property and buildings. This is particularly the case in populated areas, such as cities, towns and villages. In these areas, military forces should assume the presence of civilians and civilian objects in any area surrounding a military objective. Furthermore, they should recognise that such areas will include vital civilian resources and infrastructure, including housing, hospitals, schools, power supplies, water and sanitation systems, transport and communications networks. This requires extremely careful assessment by militaries prior to any use of explosive weapons in order to prevent or limit harm to civilians and damage to civilian objects.

Video: © ICRC, "An Anatomy of Destruction", February 2019

An explosive weapon is considered to have “wide area effects” when the area effects of the weapon are likely to extend beyond a particular military objective. This may be due to the large blast and fragmentation radii of the weapon [see Figure 1 (below), diagram 2]; the use of inaccurate weapons systems that may strike at a distance from the intended target [3]; the use of a weapon system that delivers multiple munitions across an area [4]; or a combination of these factors.

Figure 1, © Article 36 & PAX, "Areas Of Harm: Understanding explosive weapon with wide area effects", October 2016. •• Diagram 1. Combined blast and fragmentation radii of a single explosive weapon centred where the weapon actually detonates; 2. Blast and fragmentation radii are greater for a weapon with larger explosive content; 3. Inaccuracy of delivery means those blast and fragmentation effects will occur somewhere within a larger area. Where within the wider area the actual effects will occur cannot be precisely controlled. Repeated firings will land in slightly different locations; 4. Where multiple warheads are used, even weapons with smaller individual blast and fragmentation radii.

The use in populated areas of explosive weapons with wide area effects inevitably and significantly increases the likelihood of harm to civilians and damage to civilian objects given their concentration in populated areas. This necessarily requires that military forces exercise extreme caution in the choice of weapons, including avoiding the use of explosive weapons that are likely to have wide area effects. This includes situations where the weapon is being lawfully directed against a military objective if it is in a populated area.

The area effect of any given weapon system is not fixed, and so “wide area effects” are not intrinsic to specific weapon systems - although certain heavy explosive weapons are more prone to producing wide area effects than others, such as multiple launch rocket systems, that would fire a salvo of up to 40 rockets across a very wide area.

Effects radii for a 2000lb aircraft bomb (image 1) and 120mm mortar accuracy at 7000m (image 2) •• Images: © Article 36 & PAX, "Areas Of Harm: Understanding explosive weapon with wide area effects", October 2016

“Wide area effects” can occur during the use of a range of weapon systems. Whether or not they occur depends on the system itself and the way and circumstances in which it is used, including the military objective being attacked. Factors to be considered include the size of the blast and fragmentation radius of the weapon, the degree of accuracy (will it hit the target?), including the use of multiple munitions across an area, as well as the size of the target and its proximity to the area populated with civilians and civilian objects.

22mm multi-barrel rocket system’s effects at a range of 19km: a single rocket (image 1) and 40 rockets (image 2) •• Images: © Article 36 & PAX, "Areas Of Harm: Understanding explosive weapon with wide area effects", October 2016

Consideration should also be given to the specific environment in which the weapon is being used and how this can influence its effects. Tall buildings and narrow streets can concentrate and significantly enhance blast pressure in some places. In addition, building and other materials such as glass, cement, steel and other debris add to the fragmentation effect of the weapon, increasing the likelihood of harm to civilians.

© UNHCR/Susan Schulman

To understand the effects of the weapon, and assess the likelihood and scale of harm to civilians and take steps to mitigate this - militaries need to:

  • Assess and understand the scale of area effects in different configurations of use, and factor this into decisions around the choice of weapon systems. Many of these assessments can and should be made in advance of undertaking an attack;
  • Carefully assess different contexts of use to more fully understand the likely risk of harm to civilians - including direct, indirect and reverberating effects - so this can be weighed up and factored into decision-making in advance of an attack. Assessments need to be undertaken that can better inform targeting in dynamic situations, as well as in pre-planned strikes.

Most crucially, in situations where the conduct of hostilities cannot be taken outside of a populated area altogether, and explosive weapons are being considered for use in these contexts, it must be recognised that the heightened and significant risk of harm to civilians and damage to civilian objects requires a change in practice away from the use of explosive weapons in populated areas and towards strengthened protection of civilians in such situations.

Image: © Thaer Mohammad/MSF

A threshold needs to be set where there is an established presumption of non-use when the use of an explosive weapon will produce wide area effects - i.e. effects that will likely extend beyond, or occur outside, the intended target, thus affecting the civilian population. Such a requirement should be embedded in a commitment in the political declaration, and be a key requirement at a national operational level, driven by building greater understanding of the area effects of weapons and specific contexts of use, and fuller understandings of the scale and likelihood of harm to civilians based on data.

Article 36 is a specialist non-profit organisation, focused on reducing harm from weapons.

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