NATO Standard AOP-4240 Fast Heating Ammunition Test Procedures

The purpose of the NATO standard AOP-4240 Rapid heating munitions test procedures, published by the North Atlantic Treaty Organization (NATO) among allied munitions publications, is to describe test requirements and procedures to provide evidence of the response of munitions and weapon systems to threats posed by a very high heating rate.

NATO members agree that the requirements and procedures contained in this standard will be used to evaluate the response of ammunition and weapon systems to the heat fluxes characteristic of rapid heating within the surrounding incandescent flame envelope of a large liquid hydrocarbon fuel pool fire.

This standard provides three test procedures:

• A standard test procedure for determining the reaction of a munitions when heated in a large pool of liquid burning hydrocarbon fuel.
• An alternative procedure for smaller items tested using a smaller pool of liquid burning hydrocarbon fuel
• An alternative procedure using a gas-fired heating source

The test sample configuration must be of the final production standard and must comply with the condition appropriate to the life cycle stage represented by the test or be representative as approved by the national authority.

Consideration should be given to the guidance on changes in production standards and conditions given in the SRD AOP 39.1 standard annex (Annex B), such as live and inert, preconditioning, packaged and unpackaged, all round and components.

This standard describes rapid heat testing, which includes three acceptable test methods:

• Test method 1: Large pool fire (Annex A)
• Test method 2: Mini pool fire (Annex B)
• Test method 3: Fuel burner fire (Annex C)

Each test has a different physical setup to account for changes in the size of the test specimen or to reduce the amount of fuel required to perform the test. Each test is designed to provide the same, comparable, flame-enveloping heating conditions.

In test method 1, the test specimen is surrounded by rich flames from a large open hearth containing liquid fuel. The large horizontal dimensions of the hearth ensure that the flames are fuel rich and therefore heat transfer to the test specimen is highly radiative.

Fuel-rich flames and highly radiative heat transfer are achieved in Test method 2 by placing deflectors around the much smaller hearth to restrict oxygen entry.

If desired, the mini pool fire method can be used to reduce pollution. The limitations for its use are:

• The test specimen shall not exceed 630 mm in any dimension and shall not exceed 50 kg in mass.
• The mini pool fire test facility does not allow accurate measurement of overpressure and particle protrusions, which are necessary for distinguishing between Type IV and Type V response types and for hazard classification purposes. If data on these aspects are required, the test specimen should be subjected to Test Method 1 or 3.
• The requirements of the test range authority also need to be taken into account.

Test method 3 permits the cyclic use and distribution of hydrocarbon fuels. The test sample is surrounded by flames from fuels other than liquid pools. The test setup permits recognition of response types. The test requirements are as follows:

• The flame shall provide sufficient heating of the test specimen comparable to that produced by Test method 1.
• Additionally, the possibility that the incident will cause significant damage to the fuel burner fire facility must be considered.

The condition and orientation of the test sample should be applied in a manner consistent with the life cycle stage represented by the test or with a representative approved by the national authority.

Additional guidance on changes in test conditions (e.g. positioning/orientation, restraints, conditioning, marking, re-use) should be considered in the annex to the SRD AOP 39.1 standard (Annex B).

The fire tests are designed only to simulate the most intense heating conditions likely to occur in a hydrocarbon fuel pool fire. However, they do not simulate a specific in-service or accident scenario.

Explosive-filled test items involved in less intense fires or exposed to lower heating rates may remain inactive for longer periods, but the magnitude of any resulting explosive event may be more severe than an event resulting from exposure to high heating rates because more explosive material may reach dangerous temperatures while still contained within an unbreached enclosure.

Data from this test cannot be extrapolated with respect to temperature or time to obtain performance estimates under other conditions that may involve lower temperature or heat flow levels. Heat flow rates and thermal gradients within complex assemblies can become nonlinear when changes in state or loss of integrity of internal structures and components occur.

The test consists of exposing the ammunition to a fire and recording its response over time. The test is terminated upon completion of the ammunition's response or when the fuel supply is exhausted and no sustained response (such as burning, fragmentation) from the ammunition is recorded as evidence of a Type VI response.

Among the numerous testing, measurement, analysis and evaluation studies that our organization has carried out for businesses in various sectors, it also provides testing services defined in the “NATO standard AOP-4240 Fast-heating ammunition testing procedures” standard with its trained and expert staff and advanced technological equipment.