Explosive Atmosphere, MIL-STD-810, Method 511, is used to evaluate how equipment will function in an explosive fuel-air environment. This method has two procedures. Procedure I – Explosive Atmosphere evaluates the ability of equipment to operate in a fuel-air environment without causing the fuel air mixture to ignite. Procedure II – Explosive Containment evaluates the equipment’s ability to contain an explosion resulting from a malfunction.
This testing is appropriate for equipment designed for environments where aircraft, automotive, and marine fluids or vapors exist. The test is representative of conditions at or above sea level where flammable fluids or vapors are present. This testing is performed in a test chamber and should only be performed by qualified personnel.
These tests normally use N-hexane for fuel sources as these have similar properties to JP-4 and JP-8 jet engine fuel, and high-octane aviation gasoline. It is important to keep in mind that N-hexane is a hazardous material and that exposure to humans should be limited.
The fuel-air ratios are specified in detail for the explosive atmosphere test. These ratios must be homogeneous in the test chamber. Temperature for chamber is to be the highest ambient temperature that the test item is to operate in during its life cycle.
Because the corona effect makes electrical devices more susceptible to arcing and creating sparks, both procedures are performed at simulated altitudes. For Procedure I the test item is normally exposed to a chamber pressure of 40,000 ft. (12,200 m) plus 6,600 ft (2,000 m).
The specified volume of n-hexane is introduced into the chamber and is allowed to mix and circulate with the chamber air. The pressure is then adjusted to 40,000 ft. (12,200 m). After each chamber pressure and corresponding n-hexane a test sample of the fuel-air mixture is subjected to a spark to verify the mixture’s explosiveness.
Because of the low levels of oxygen present at the 40,000 ft. level, ignition may not always occur. If the test sample is not ignited the chamber must be purged and the test restarted.
If the fuel-air mixture is verified, then the test item is exercised to simulate all operational modes. If the test item does not cause ignition, the sequence is repeated for at least three more sequences at lower altitudes. The final test occurring at site ambient pressure.
Procedure II Test Sequence
For Procedure II – Explosion Containment, the test item of model of same volume is installed into the test chamber. Humidity, dew point and specified operating temperatures are established in the chamber. The air pressure is set for a simulated altitude of 6,600 ft (2,000 m).
The fuel-air mixture is introduced, and the chamber pressure is returned to site ambient pressure. The mixture within the test item is ignited and if explosion occurs the test is complete.
Detailed Environmental Test Plan Templates
CVG Strategy offers EZ Test Plan Templates for MIL-STD environmental (climatic/dynamic) and EMI/EMC test documentation. Our Detailed Environmental Test Plans (DETP)s are written as specified in MIL-STD-810 Task 405. They are available for specific applications such as Ground Mobile, Ground Stationary, and Shipboard Controlled, Shipboard Uncontrolled, and Aircraft Military.
These DETPs include appropriate methods, (such as Explosive Atmosphere MIL-STD-810 Method 511) addendums for product specific information, test labels for photo identification and data sheets for collection of required data. Profile (LCEP).
Our Electromagnetic Interference Test Plans are written as specified in MIL-STD-461. They contain the test methodology, addendums for product specific information, test labels for photo identification and data sheets. These plans are available for procedures listed in MIL-STD-461 and are also available for MIL-STD-1275, MIL-STD-704, and MIL-STD-1399-300.
Custom Test Plans are also available for applications not covered in the EZ Test Plan offerings. These plans can be written for any number of applications and their relevant standards.
Put CVG Strategy’s Experience to Work for You
Companies of all sizes, from start up to established product developers, face challenges in product test and evaluation. This can particularly be the case when a product is developed for a new market sector or expanding sales internationally.
Properly tested products prevent costly product recalls, product redesign, and product liability. They maintain customer satisfaction and keep your company’s reputation in good standing. Contact CVG Strategy to see how our services can assist your engineering team with Explosive Atmosphere MIL-STD-810 Method 511 or any other test and evaluation concern.