Blast blankets for covering and containing blasts and explosions; blankets for covering and containing blasts and explosions and for containing the products of blasts and explosions; blast blankets containing a water-absorbent filler for covering and containing blasts and explosions; blast blankets containing super-absorbent polymers, water-absorbent gels, cotton fibres, wood pulp and mixtures thereof for covering and containing blasts and explosions