Airtight glass bottles, sealed aluminium laminated packages, and sealed metal cans give complete protection against vapour and liquid. Wooden boxes not sealed for the exclusion of air give almost no protection against vapour and liquid. Waxed paper boxes sealed for the exclusion of air give good protection against vapour and fair protection against liquid. Untreated wrapping papers give poor protection against vapour and very little against liquid. Coverings of sod and earth give good protection against vapour and liquid.
Overhead shelters give protection against liquid sprays and splashes.
Closed buildings give protection against liquids but often not against vapours, unless overpressured with filtered air. Generally, double layers greatly increase the protective efficiency of packaging materials. All food exposed to chemical attack which has not been protected by agent-proof containers or in fully protected stores must be considered contaminated. Monitoring for volatile agents only may be undertaken by putting the food into a clean plastic bag and sampling the air in the bag with suitable detection equipment. Where arsenical contamination is suspected, the food may be suspended in water and the water tested with a water testing kit.