A potential munition response descriptor change has been analysed during past NIMIC workshops.

Why change and what could be the new content of responses descriptors have been presented at the 1998 IMEMTS symposium by the NIMIC team, in the paper "A synopsis of the NIMIC workshop on Insensitive Munitions testing".

From these elements, Club MURAT "standard and label working group", has performed several simulations comparing test result classification with current descriptors and with new potential ones.

From these simulations, Club MURAT has derived some suggestions. These suggestions are oriented to preserve stability and visibility on IM signature.

The current description of response types of munitions to stimuli is given the most completely in AOP 39, June 97 "Guidance on the development, assessment and testing of insensitive munitions (MURAT)". This description contains an old two-page text (§ 6.7) which explains qualitatively the five types of response. "Propulsion" and "no reaction" are also described.

Annexe D provides guidance on the interpretation of the types of response. It completes the munition behaviour, by a recent detailed quantitative description of expected effects (blast, projection of energetic materials, projection of fragment, other such as heat fluxes). "Propulsion" and " no reaction" are not described. This technical table is given in appendix A of our paper.

Other NATO documents generally retain (or refer to) only the old part of this description, which situation is normal from anterior documents (Stanags 4240, 4241,4396,4382 – all edition 1) – but unexpected for more recent ones (AOP 38 – March 98 or Stanag 4240, edition 2, draft 5).

In our analysis, current description means description established by AOP 39.

This was extensively presented by NIMIC at the 98 IMEMTS – the material coming from a NIMIC workshop.[1]

With the current Annex D of AOP 39, this is no more completely exact:

In fact, quantitative thresholds are defined:

• for blast, to access type III, IV and V;
• for fragments, to access type V ;
• for heat flux to enter type V.

However it is true to say that:

• blast is not completely defined: is it side-on or reflected pressure? - no blast duration is indicated;
• fragment and heat flux don't cover quantitatively the types III and IV.

We must also add that these effects are given to assist in classifying and not to rule it.

Table 1 - Threshold criteria" -– NIMIC proposal [1]

We firstly observe that overpressure is better defined that in AOP 39, though, still, not thoroughly: the duration of blast, an important factor of lethality is not given.

A second observation is related to consistency of criteria.

The lethality by blast may be:

• primary : crushing hollow parts of the human body such as lungs (direct lethality),
• secondary : through projected fragments,
• tertiary: through displacements of human body (dynamic effect).

At 35 kPa, it is generally acknowledged that direct lethality is not possible, whatever is the duration.

Secondary lethality is viewed through debris and fragments effects.

Tertiary lethality at 35 kPa must be evaluated from induced body velocity [2]

Table 2 – Human body velocity from 35 kPa

[3] gives 50 % of skull fracture at 5.4 m/s and 99 % at 7 m/s. In case of a fall or a projection of human body against a hard surface, induced by the blast, lethality is quite probable at 10 m/s.

So, for example at 50 m from the munition, we have some lethality from blast; and fragment criterion which is quite severe (no fragment – at all) becomes inconsistent with blast criterion

Table 3 – Levels of Response Definitions" - NIMIC proposal [1]

The types considered by NIMIC are illustrated hereunder

Fig 1 – Current /new types equivalence

NIMIC analysis clearly points out that transition to new definitions will create some trouble:

• objectives will be renewed, and technology will have to be reviewed ;
• existing IM realisations may be no longer compliant.

In the countries such as France which have already realisations and programmes in IM area, it is a need to put under scrutiny this possible transition.

Club MURAT "standard and label working group" (SLWG) realized in 1999 different simulations – Two of them are presented hereafter.

In these simulations, we retain as working hypothesis that the new definitions are those considered by NIMIC

In both simulations, we analyse actual fire tests reports (FCO) – We present the result according to the current criteria and we reanalyse the test reports according to the possible new criteria.

Data and judgement are given in table N°4 hereafter – The result was classified Type V response according to the current criteria.

Absence of heat flux measurement does not allow to judge conclusively with new criteria – though the new criterion is less severe: it's less sensitive to a plume effect of short duration. During a FCO test, it may be difficult to measure extra heatflux, because of curtains, preventing wind effects

However "type V" response could be assigned with this test result.

(1) difficulty to measure at 5 m (hearth size and presence of curtains)

It's related to an IM version of a massive warhead ( ³ 50kg of energetic material), a figure of which is presented hereafter - Ref. [5]

Figure 2 – tested warhead

With the old (non-IM) version of this warhead, a type I reaction is observed in a FCO (according to Stanag 4240).

With the IM version, at FCO, we observe: no fragmentation of casing but projection of an end cap and HE chunks in a certain direction, up to 80 meters.

Judgement allowed to assign a type IV to this result with current criteria.

Due to a "no fragment" criterion at 50 m, this result would be assigned a type II with new proposed criteria

Also, there would be no bonus with this IM version, which is however notably safer than the old one.

• tests Stanags would have to be reviewed;
• interpretation of existing trials may prove impossible, due to absence of a decisive value (heat-flux measurement or fragment observation);
• the "no-fragment" criterion will be difficult to achieve;
• with such a "no fragment" criterion, there may be no visible benefit to prevent a detonation for some large warhead

These simulations have allowed our working group to better understand new criteria and to identify difficulties.

We can also suspect another fact: massive munitions will pass uneasily, when small munition may pass more easily, in spite of a bad reaction of the energetic material, which may be tricky for users.

From our experience, we would propose some suggestions related to:

• the nature of the project
• the viability of the project
• the visibility of objectives

The purpose of the project is to give quantitative data on effects, and to directly guide safety people, when they have to write their emergency rules or to intervene.

However the quantitative data would be based on one (or two or three) munition effects.

Hazards may come from stacks of munitions.

There is, possibly, an amplification process of effects, when passing from one, to many munitions. The amplification process seems frequent on thermal flux values = IM does not guarantee non-simultaneous burning.

If the blast comes from bursting of elements, simultaneous burstings are quite improbable, though not impossible.

With a "no fragment" observation from one single munition, one can reasonably expect the same from a stack: there is no "amplification process"; by this side, this criterion is quite attractive.

A point also quite attractive in the project is the possibility of a "no reaction" type – Available technology allows this result, especially under bullet impact. This decisively improves the survivability of platforms, such as aircrafts. This type of response escapes to the amplification process.

However, this new type of response could be very simply added to the current types, without entering the great project.

In abstract, we observe that the criteria of "no severe hazard" at a certain distance achieved with one item, may or not be achieved with a stack of the same munitions at this distance.

This proposed criteria, which take into account the environment, could be understood as a greater help to "safety people".

However, we think one has to be very careful. In fact this new criteria will not allow a direct relation with safety rules (due to differences between single munition effect and a stack of munitions effect).

New descriptors are quantitative values of blast, thermal flux and fragment.

New descriptions are based on threshold values at certain distances.

A technical work has yet to be realized before these elements can be adopted:

• new descriptors are not quite finalized : has blast to be characterized by a pressure duration?
• new thresholds have perhaps to be adapted ;
• feasibility of obtaining adequate data through testing must be investigated ;
• simulation of new classification approach should be undergone ;
• exact benefit from new system has to be estimated.

Such a work can only be undertaken only under the NATO group AC 310 authority.

A NATO Working group, or a NIMIC workshop could be the frame of such an effort.

If NIMIC way is retained, the workshop should be organized as a "consolidation workshop".

A hasty decision, without such a work, could be more damaging than a "do-nothing" option.

IM awareness has still to be maintained awake among system teams and Forces.

Also the visibility of old objectives should have to be kept up during a transition period. And

NATO countries IM community would require some standard "material" to explain and accompany the change. This written information should be produced by NATO and available at the proper time

IM process has been going on for more than 20 years – Current classification of response of munition is a cornerstone both:

• in each country to develop IM technology and incorporate it ;
• in NATO community to understand each other.

Transition to new response descriptors and new criteria must be considered as a "great project".

Such a transition requires preparation, organisation and explanation.

Technical work (new criteria to complete, test procedures to adapt, simulation to conduct) must be realized – before the decision be taken – in order to be sure of viability of the project.

Visibility of objectives must be maintained during the transition period and after through a proper information.