217. Choice of means and standard of reasonableness.

The choice of means for ensuring the positive obligations under Article 21 is in principle a matter that falls within a state's margin of appreciation, and the scope of any positive obligation must be interpreted in a way which does not impose an impossible or disproportionate or excessive burden on the authorities, bearing in mind, in particular, the unpredictability of human conduct and operational choices which must be made in terms of priorities and resources2. The standard demanded for the performance of the operational duty is one of reasonableness3: the failure to perceive the risk to life in the