A/72/178 is unavoidable, the degree to which and the manner in which force is employed may not be more harmful than strictly necessary. 13 Finally, in temporal terms, the use of force is unlawful if, at the moment of its application, it is not yet or no longer unavoidable to achieve the desired lawful purpose. Therefore, any law enforcement operation involving the use of force requires a constant reassessment of its necessity to achieve the desired purpose. Should the circumstances evolve so as to permit the achievement of that purpose through less harmful means, force may no longer be used. C. Principle of proportionality 10. While the principle of necessity requires a factual assessment of t he least harmful means that can be expected to achieve the desired purpose, the principle of proportionality involves an additional and separate value judgment as to whether the harm expected to result from the use of force can be justified in the light of the benefit of the desired purpose. Even if force is necessary for the achievement of that purpose, it can only be permissible if the resulting harm remains proportionate compared to the seriousness of the offence and the importance of the desired purpose. 14 Thus, irrespective of considerations of necessity, the requirement of proportionality defines an absolute upper limit for the force that might be permissible to achieve a specific lawful purpose (A/HRC/26/36, para. 66). The “harm” to be weighed in the proportionality assessment does not necessarily have to be of physical nature, but can also involve mental suffering and emotions of humiliation and distress. 11. A proportionality assessment must always be made in the light of the circumstances of each case. As a general rule, potentially lethal force must not be used except where strictly necessary to: (a) defend any person against the imminent threat of death or serious injury; (b) prevent the perpetration o f a particularly serious crime involving grave threat to life; or (c) arrest a person presenting such a danger or prevent their escape. Intentionally lethal force may only be used when strictly unavoidable in order to protect life from an unlawful attack. 15 For example, even the aim of lawful arrest cannot justify the use of firearms to stop a thief or pickpocket not otherwise posing a threat to life and limb. In such cases, considerations of proportionality require that the risk of the suspect escaping arre st is to be preferred over the risk of causing the suspect’s death or serious injury. Other factors that may be relevant in evaluating the degree of force that is proportionate include the individual’s behaviour, age, gender and health. D. Principle of precaution 12. Even if the use of force is necessary and proportionate in the immediate circumstances of a case, it may nonetheless be unlawful if it results from a failure to plan, organize and control operations so as to minimize harm, respect and pr eserve human life and avoid any excessive use of force. 16 13. In particular, States should thoroughly train their police forces to avoid situations in which the use of force will become inevitable and equip them with various methods and types of weapons and ammunition allowing for a differentiated use of force, including “less lethal” incapacitating weapons and self-defensive __________________ 13 14 15 16 17-12326 Ibid., principle 5 (b). Ibid., principle 5 (a). Basic Principles, principle 9, and European Convention on Human Rights, art. 2 (2). Basic Principles, principles 2, 3 and 5 (a) and (b). 7/24