What is an on-site inspection?

An on-site inspection is a meticulous search of a clearly defined inspection area to gather evidence on whether or not a nuclear explosion has taken place.
Radiation protection is a key issue for all on-site inspections. Here inspectors are scanned for radiation before entering the base of operations.

An on-site inspection (OSI) is the final verification measure under the Comprehensive Nuclear-Test-Ban Treaty (CTBT) and follows up suspicious but inconclusive evidence of a nuclear explosion obtained by the CTBTO's global network of monitoring stations.

Once the CTBT has entered into force, a State Party will be able to request an on-site inspection if it suspects that another State has conducted a nuclear explosion. The inspection is authorized to proceed if it has been approved by at least 30 of the States that make up the 51 State members of the organization's executive body, the Executive Council.

The State Party subjected to such an inspection cannot refuse to allow it to take place. One of the main benefits of an on-site inspection regime is that it deters potential violators from conducting nuclear explosions in the first place. It thus increases confidence in States’ compliance with the Treaty.

Rapid deployment into the Field

Fourteen trucks were used to transport equipment and material to the site of one of the build-up exercises for IFE14.

As there is only a narrow time window during which some of the conclusive evidence of a nuclear explosion can be obtained, an on-site inspection must begin as soon as possible once it has been approved. Indeed, the Treaty specifies that the CTBTO has only six days from receiving the inspection request to transport the inspection team and an estimated 100 tons of equipment into the country subjected to the inspection. Following this, the inspection team has to submit a first progress report within 25 days of the approval of the inspection by the Executive Council. The inspection is scheduled to last 60 days unless the Executive Council decides to discontinue the inspection earlier or approves requests from the inspection team to extend the inspection by up to 70 additional days to a  maximum duration of 130 days.

At the centre of an inspection is a team of 40 inspectors including experts in seismology, geophysics, radionuclides, radiation protection, communications, logistics and IT.

The Inspection Team

Representatives of the inspected State Party (left) and members of the inspection team signing the preliminary findings document during a recent exercise.

At the centre of an inspection is a team of 40 inspectors including experts in seismology, geophysics, radionuclides, radiation protection, communications, logistics and IT. The inspectors can use a range of increasingly intrusive techniques to gather evidence within an inspection area of up to 1,000 km². Soon after the conclusion of an inspection, the inspection team must report all findings to the CTBTO’s executive body which will make the final assessment as to whether the Treaty has been violated, i.e. whether or not a nuclear explosion has taken place.

Inspected and Requesting State Parties

The Treaty provisions for the conduct of an on-site inspection reflect the intention to maintain the balance between an effective inspection and the protection of the Inspected State Party’s (ISP) national security interests. The ISP must provide full access to the inspection area and give all necessary assistance to the inspection team to carry out its activities. The inspection team for its part strives to conduct the inspection without causing undue disturbances for the ISP. In addition and upon request, the team must share all information, data and samples with the ISP.

The political sensitivity of an OSI finds another expression in the Treaty when it deals with unjustified OSI requests. In the case that an OSI request turns out to be “frivolous or abusive”, the requesting State Party may be subjected to rather stringent measures, such as paying for the costs of any preparations already made; having its right to request another on-site inspection or to serve on the Executive Council temporarily suspended.

Playing out their roles helps everybody involved - future inspectors, planners, administrative experts and logisticians - to have a better understanding of their function in an on-site inspection.

Building-up the OSI Regime

Regular exercises and field tests help to test and improve techniques and procedures of an on-site inspection.

On-site inspections can only be invoked once the Treaty has entered into force. The Preparatory Commission for the CTBTO is now working to build up the OSI regime, so that the OSI capability will be available following the Treaty’s entry into force. Current activities include the development and preparation of an OSI Operational Manual, a list of equipment for the training of inspectors, a programme for the training of inspectors, and the acquisition or making provision for the availability of relevant inspection equipment.

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