The STAC should be activated by the lead responder through the SCG's generic procedures for obtaining scientific and technical advice. The provision of scientific and technical advice should be part of the first considerations of a tactical or strategic group. Where other arrangements exist for specific types of emergency, as described at 7.2-7.4 above, they should be recognised when consideration is being given by the SCG for the activation of STAC arrangements. However, a senior public health professional ( i.e. Director of Public Health or deputy) may recommend to the SCG chair that a STAC needs to be established due to the potential impact on the health of the local population from an actual or evolving incident.
A meeting of the STAC should be held as quickly as possible to carry out the initial risk assessment and to identify the ongoing requirements for specialist advice to the coordinating group.
Immediately following the occurrence of an emergency the lead responder(s) may be without a coordinated source of expert advice. In this situation the primary source will be local area expertise, e.g. local Directors of Public Health, Environmental Health Officers and FRS HAZMAT Officers. They may be able to provide an early assessment of the likely or actual impact of the emergency, which may include advice on first responder safety. 
Initial STAC discussions and provision of advice to the lead responder/s can be conducted by telephone/teleconference/ IT links. Adequate 24/7 contact and communications arrangements for STAC members should therefore be in place.