I have a walkout basement with a covered front porch 4'x 9', so the space under the porch is surrounded with concrete 9" walls. I want to cut a door in the basement in the concrete wall, empty the gravel and other stuff from that space and turn the space into a storm shelter. I will cut a small door in the 4' section which I enter through a closet. The wall is load bearing as above it is a concrete slab, and 10' of brick. What do I need to use for a header"?
Don't head off half cocked with internet advice and a 10" brick wall above. Hire a structural/civil engineer, and get an answer you can bet your house and/or life on - because you will be doing exactly that. Having got the advice, follow it carefully.
Given that you say "small door" your engineer might be able to give you a less painful solution by using a round-topped door that will act somewhat like an arch, for instance.