Strainers is safety devices used to prevent external fire entering in to the tank or inside the pipe line & ducts & to prevent flame  spreading from in to or out of plant & equipments flame arresters are normally installed on the end of the line or above the vessel, where hazardous gases are normally vented out. The internal element or flame bank is made of metal sheet, the gas is allowed to pass along with the element which prevent fire entering in process on the event of external fire sizing / designing can be done with reference to API - 2000. Flame bank is so designed that the pressure drop is negligible . In any process or plant which us flammable gas, or vapour that could conceivably ignite flame, flame arresters must be used. To assist yours requirement the details such as the fluid, gas & vapour contains & tank size, apacity in ltr. pumping rates in & out from storage tank be specified, where the flame arresters are required.