How to produce and use odour soaks as part of an effective detection dog training programme

What is this note about?

This note provides guidance on how to produce, store, use and dispose of odour ‘soaks’. The note focuses primarily on producing effective explosives odour soaks, but the general principles can also be applied to other target materials. Soaks can be a useful tool to assist continuation training, particularly when the use of explosive samples is impractical for logistical, safety or contamination control reasons. However, in order to be effective, soaks must be produced in a way that ensures appropriate odours are captured on them. 

Who is this note relevant for?

All dog handlers or instructors training and deploying detection dogs and any personnel involved in soak production.

Introduction

A soak is a training sample that has been made by exposing an absorbent material (called a soak matrix) next to, but not in direct contact with, a training sample such as an explosive, within a sealed container. The matrix becomes impregnated with the odour of the explosive and can therefore be used on its own as a training aid without the safety, logistical or contamination control issues associated with using actual explosive samples.

It is important to note that soaks may not replicate the full odour of the original explosive sample and are therefore not recommended for initial training or as the main component of continuation training. Soaks instead provide a convenient means of carrying out continuation training when the use of bulk explosives is impractical (e.g. training in an operational environment). These training aids also provide an opportunity for the dogs to search for a small/different odour plume, making them an effective part of a training aid suite to encourage generalisation [1]. Whenever soaks are used during training, it is essential to also place out ‘blank’ soaks (clean, uncontaminated samples of the matrix material) to ensure the dog learns to ignore any background contaminant odours arising from the manufacture, storage, and/or handling of the soaks. Further information about the production and use of blanks is available in a separate guidance note [2]. 

Soaks can theoretically be produced using any explosive sample (or other target material), though they are likely to be more appropriate for those that produce stronger odours.

Preparation

The recommended materials for the soak matrices are glass microfibre or cellulose filters sourced from laboratory suppliers (25mm diameter is recommended). Laboratory-grade products are most suited to dog training as they are designed to have minimal contaminants and undergo strict quality control measures to ensure consistency between batches. If sourcing these products is difficult, clean blank paper (e.g. printer paper) can be used instead (approximately 25mm to 40mm diameter pieces recommended). When producing the soaks, airtight glass jars with clamp-type lids and silicone seals are recommended to ensure the explosives odour is contained within the jar to allow maximum uptake by the soak matrix. Glass containers should be used to minimise the potential for odours to be transferred between containers. For safety reasons, explosives should not be put in containers with screw threaded lids.

It is recommended that small (e.g. 5g) samples of explosives are used, to make it easy to ‘soak’ the matrix material with the explosives in an airtight jar, without direct contact. It is easiest to source these small explosive samples pre-cut from the supplier (note that any dividing/cutting of explosives is considered explosives processing and requires appropriate licences, approvals and training to be in place). 

Soaks should be made in a clean, uncluttered environment that contains as few noticeable background odours as possible.

 Both the blank and explosives soaks should be made by the same person, on the same day, in the same environment with the blanks being made first. Blanks must not be prepared whilst wearing clothes that have been worn to handle explosives. The area chosen for preparation should not be contaminated with explosives to prevent the blank soaks absorbing background explosives odour. Members of staff making soaks should wear clean clothes (suitable for wearing when handling explosives) and avoid wearing any strong odour products e.g. perfume or aftershave. Identical soaks can be produced in batches at the same time; numbers per jar will vary depending on size of soak matrix and jar used.

Storage and transport

• In order to avoid the soak matrix materials becoming tainted with unwanted odours prior to preparation, they must be stored in their original packaging in an environment where there are no strong background odours.
• Once prepared, storage and transport of odour soaks does not fall under the storage and transport of explosives regulations, providing there is only explosives odour on the material (i.e. no actual explosive present).
• Explosives and blank soaks may be stored in different environments as long as the packaging is tightly sealed. It is best practice to store them in a cool, dry place, out of direct sunlight.
• Soaks should be kept in their production packaging until they are ready to be used for training..
• As a guide, soaks should be used as soon as possible, and within 2 weeks of production. The exact shelf-life can be adjusted if required depending on how easily dogs detect them.
• If any soaks are thought to have been inadvertently contaminated, all soaks from the same jar/packaging must be disposed of and new soaks made.

Contamination control in the training environment

• Providing that the pieces of matrix do not come into contact with the explosive, the soaks produced have a low chance of contaminating the training environment. However, the potential for environmental contamination should be considered when concealing soaks for training purposes. Soaks produced from NG and EGDN-based explosives in particular can cause significant odour contamination. 
  - A barrier (e.g. paper) should be placed between the soak and the environment to reduce potential for accidental environmental contamination.
• If the matrix material comes into direct contact with the explosive it becomes contaminated with explosive particles. Soaks produced in this way are likely to be inconsistent as training aids and are highly likely to cause long-term contamination of training venues due to the transfer of these explosive particles. The production and use of soaks through direct contact with explosives is therefore not recommended.
• Separate blank and explosives soak forceps must be used to handle soaks when placing them out in the training environment, and these should be kept apart from each other at all times. New plastic (or carefully washed stainless steel) forceps should be used each session.

Training using soaks

It is important to keep in mind that soaks may not fully represent the odour of real explosives. Therefore, real explosive samples (not soaks) should be used during: 

• Initial odour learning. 

• Licensing and accreditation activities to assess odour recognition. 

• The majority of continuation training. 
   

Soaks can be used for a proportion of continuation training including stand-based (odour ID) and all standard conventional searches. The following guidelines should be followed:

• Each soak should be used for up to 2 hours then discarded, or earlier if there is evidence dogs are consistently failing to detect them.
• Blank soaks must always be put out during soak training. This ensures the dog learns to detect the target odour only and ignore the blank matrix material (or any odour contamination arising from the preparation process).
• All soaks should be fully concealed so that dogs cannot see them.
• Dogs should be rewarded for correct indications on explosives soaks using the dog’s standard rewarding technique and frequency. All indications on blank soaks must not be rewarded.
• All soaks should be collected following completion of a search and disposed of correctly at the end of the day (see below).
• Minimise handling of soaks during training as much as possible. Change gloves in between handling blank and explosives soaks, and soaks of different explosive types.

Health and safety

Explosives odour soaks, when prepared as detailed in this guidance note, should not contain any particulate explosive materials and should therefore not pose an explosive hazard. The matrix material should be handled in accordance with the instructions and safety information provided by the manufacturer. Once prepared, soaks should be handled using clean forceps to avoid contamination and while wearing suitable disposable gloves (conforming to EN374 class 3). Dogs should not be allowed to come into direct contact with soaks at any point, to avoid them inhaling or ingesting the matrix material.

Explosives Regulations and soak production:

It is important to note that the processing and storage of explosives during the soak period is subject to the Explosives Regulations, and complying with these is the responsibility of the individual establishments producing the soaks [4]. 

Any building used to produce soaks must also meet the general requirements for explosives security [5].  

Seek expert advice if you are in any doubt as to whether your planned soak production methods will comply with legal requirements.

Disposal

• Never re-use an old soak. They should be disposed of after use and never returned to the production jar or soak packaging. This is because environmental contaminants picked up on the soak during use will contaminate the remaining soaks.
• Blank soaks can be disposed of in conventional refuse, following the manufacturer’s disposal advice.
• To prevent contamination, explosives soaks should be treated using the same procedures as explosives contaminated waste, e.g. explosives soaks should be disposed of in the same way as gloves used to handle explosives training kits.

Associated guides and information

[1] How to train your dog to generalise across varying types and sizes of targets (DSTL/PUB89074)
[2] Using blanks and interferents to ensure effective detection dog training (DSTLl/PUB111065)
[3] Why and how to control contamination (DSTL/PUB89664)
[4] Explosives health and safety - HSE website
[5] Storing explosives - HSE website