Emerson PACSystems PAC8000 I/O Modules interface to safety system field wiring via Field Terminals. The IO Modules and the Field Terminals mount on carriers that provide mechanical support, but also connect the internal communication bus and power supply connections to the Modules.

The Emerson PACSystems PAC8000 I/O Modules are certified for use in safety-related applications up to and including SIL 2. The SafetyNet System achieves this certification with a 1oo1D architecture. The SafetyNet IO Modules have been designed specifically for safety-related applications and are certified on the basis of the excellence of their design. The certification does not depend on "proven in use" data.

The IO Modules perform comprehensive internal diagnostic tests as an essential part of ensuring that the IO can carry out the required safety function. If the SafetyNet IO Module's internal diagnostics detect a fault that would prevent the SafetyNet System from carrying out its safety function,then it will initiate a controlled shutdown. A controlled shutdown has two objectives – firstly, to ensure that the IO Module enters its failsafe mode; and secondly, to record sufficient data to allow the reason for the shutdown to be determined. If a SafetyNet Module enters a controlled shutdown, then all IO channels are deactivated: input channels are not scanned; and output channels are de-energized.