Many sealants, adhesives, and spray polyurethane foams release VOCs and other potentially harmful chemicals when curing. The product manufacturers' installation and safety procedures should be followed when performing work, and ventilation should be provided as required: opening windows, using temporary ventilation fans or using full respiratory equipment, depending on the nature of the work being performed. In some cases, for example when using large quantities of spray polyurethane foam in attics, roofs, or walls, contractors need full respiratory equipment while in the work area and occupants may need to leave the house for up to 24 hours after spraying, where all windows are kept open for a full-house flush. Note that there is an increasing number of available products that release little or no VOCs.