Summary: Anyone specifying blast protection for a defence facility or high security industrial site eventually runs into the same reference point: MK117. It shows up on tender documents and datasheets, usually without much explanation. The MK117 bomb blast door standard is one of the most widely used benchmarks for rating blast resistant doors, and understanding it helps you read a spec sheet the way an engineer does.
What Is the MK117 Bomb Blast Door Standard?
The MK117 is a real munition, a US general purpose bomb, and its blast profile became a practical benchmark for door manufacturers well before it appeared in any single formal code. When a datasheet references the MK117 bomb blast door standard, the door has been engineered, and ideally tested, to resist a cased 500lb charge detonating at 100ft standoff. In the absence of further threat details, this profile stands in as a reasonable general purpose bomb scenario.
What Does a 500lb Bomb Blast Resistant Door Actually Withstand?
A 500lb bomb blast resistant door is built around the equivalent TNT weight generated by the MK117 profile, roughly 488lb once converted from the H6 or Tritonal fill. Engineers use that figure, plus reflected pressure and impulse duration, to calculate structural response, deflection limits, and rebound resistance for the leaf, frame, and anchoring. It’s a heavier design case than most commercial blast ratings, hence the thick reinforced steel plate construction.
How Does the 25 psi Blast Door Rating Compare to Other Standards?
A 25 psi blast door rating sits in the high protection category, well above light and moderate ranges used for general industrial risk. For comparison, some petrochemical projects rate doors in bar rather than psi, and a 40 bar blast resistant door sits at a comparable or higher severity depending on standoff and charge assumptions. What matters is matching the rating method your risk assessment calls for, rather than assuming psi and bar figures convert directly.
Should Blast Doors Also Meet Fire Resistance Requirements?
Yes, in most high hazard applications. A door engineered to the MK117 bomb blast door standard still needs to work as a fire barrier if a blast is followed by fire, which is why specifications often call for a BS 476 blast door fire rating alongside it, sometimes up to 180 minutes.
Conclusion
The MK117 bomb blast door standard gives engineers a consistent, well understood benchmark for one of the more demanding blast scenarios a door can face. Getting it right means matching structural design and test evidence to that exact threat profile, not a generic assumption. At Ecotone Systems, blast doors are engineered against recognised benchmarks like MK117, with blast and fire performance built in from the design stage.
Frequently Asked Questions
What bomb does the MK117 standard actually refer to?
It refers to a US general purpose bomb with a cased 500lb charge, used as a design benchmark for blast door testing.
Is 25 psi considered a high blast door rating?
Yes, a 25 psi blast door rating sits in the high protection category, typically specified for defence and high security facilities.
Do MK117 rated doors also need fire resistance?
The comparison depends on standoff distance and charge assumptions, so a 40 bar blast resistant door isn’t automatically equivalent without recalculation.
Why does Part 20 matter if doors are tested under Part 22?
Often yes, especially where a blast could be followed by fire, which is why fire ratings are frequently specified alongside blast performance.
Are MK117 rated blast doors used outside defence facilities?
Yes, the standard is also referenced for petrochemical, power, and other high hazard industrial sites with elevated explosion risk.
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