Does the assured only have to prove that a loss has taken place? He must usually prove one more factor to discharge his burden of proof – he must prove that the loss was accidental. Lord Birkenhead made it clear in British & Foreign Marine Insurance Co. v. Gaunt [1921], that damage must be due to some fortuitous circumstance or casualty. The interference with the insured property must demonstrate some abnormal circumstance, therefore, even without specific exclusions. Put simply, ARPI will not usually cover loss caused by ordinary wear and tear, inevitable depreciation, the deliberate actions of the assured or a defect which is latent and inherent in the insured property.
This is not to say that loss against latent defects and inherent vice cannot be insured, but as will be seen they are not usually covered. We should consider this proposition in more detail and analyse the reasoning behind it – questioning whether a further distinction should be drawn between “non-accidental” and “self-induced” loss.
Although there are many cases both in the UK and in the US which consider the elements which constitute accidental loss, the issue is almost always bound up with “who has to prove what!” The problem cases nearly always arise where there is some doubt as to the peril causing the loss.
In summary, the policy may say “All Risks”, but it would perhaps be better described as “All external and accidental risks not otherwise excluded”.
The interaction of the burden of proof, fortuity and the associated exclusion clauses are pretty much discussed online and the information are easy to be found.