Except as otherwise provided for in article 10 of this Convention, any authority competent to exact forced or compulsory labour shall, before deciding to have recourse to such labour, satisfy itself:

(a) That the work to be done or the service to be rendered is of important direct interest for the community called upon to do the work or render the service;

(b) That the work or service is of present or imminent necessity;

(c) That it has been impossible to obtain voluntary labour for carrying out the work or rendering the service by the offer of rates of wages and conditions of labour not less favourable than those prevailing in the area concerned for similar work or service; and

(d) That the work or service will not lay too heavy a burden upon the present population, having regard to the labour available and its capacity to undertake the work.