78 Resource book on the use of force and firearms in law enforcement Chapter 6. Guidance for the most commonly used instruments of force in law enforcement This chapter looks at different instruments of force that are commonly employed around the world, including batons, handcuffs and other restraints, dogs and horses, chemical irritants, water cannons, electroshock weapons, launched kinetic impact projectiles and firearms. It discusses the tactics that should guide their use based on international human rights norms and standards, as well as recognized good practice. This guidance should be included in domestic policy and regulations. 6.1.  General principles for all instruments Consistent with the principle of legality, prior to their deployment, all the instruments of force discussed in this chapter should be appropriately tested, properly authorized, and law enforcement authorities should develop regulations or other authoritative guidance for their use. The regulations should address the instrument, and where applicable its ammunition, how it is used and in what circumstances.164 They should expressly prohibit modifying an instrument of force, for example to make it more potent by putting a metal knob at one end of the baton, increasing the weight of the truncheon etc. In countries where it is common practice to issue an instrument of force on a long-term basis to an officer, it should be regularly checked for modifications and verified whether it is still fit for purpose. Use of any of the instruments discussed in this chapter should only be justified through establishing the legal authority to apply the force and reasonable objective grounds for doing so. It is important to note that each single application of the instrument needs justification instead of just the initial instance of use. Therefore, law enforcement officials should always: • Assess the situation. • Decide whether force is required or whether there is another means to achieving the objective. • Decide what maximum use of force is permissible. 164  Note that in situations of self-defence law enforcement officials are allowed to use anything that is at hand, as long as it is proportionate and they will have to account for it afterwards.