MHK ISDB/Tests/Safety Function/Emergency Stops

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Safety Function: Emergency Stops

Purpose

An emergency stop shall provide operators with a quick, easily and safely accessible button(s) that overrides the MEC controls and causes all moving parts to stop in a safe position. As approaching or boarding a MEC to push the emergency stop can be hazardous, MECs should be equipped with a remote stopping feature that can be activated from a vessel operating near the device and from a shore station. Once activated, all power to components and output from the MEC should be terminate. The goal is to avert or reduce a hazardous event by rendering the machine safe. It is also recommended to have a redundant stop that can be activated even under a complete loss of power.


Overview for Open Ocean Testing

There are three categories of emergency stops; the appropriate one should be determined by a risk assessment:
  • Category 0: Stopping by immediate removal of power to the machine actuators (i.e., uncontrolled)
  • Category 1: A controlled stop with power to the machine actuators available to achieve the stop and then removal of the power when the stop is achieved
  • Category 2: A controlled stop with power left available to the machine actuators

Standards state that an emergency stop should satisfy the following requirements:

  • Shall override all other functions and operations in all modes
  • Power to the machine actuators that can cause a hazardous condition shall be removed as quickly as possible without creating other hazards
  • Reset shall not initiate a restart
  • Actuators of emergency stop devices shall be colored RED and the background immediately around pushbuttons and disconnect switch actuators shall be colored YELLOW.
  • The actuator of a pushbutton-operated device shall be of the palm or mushroom-head type.
  • Emergency stop devices shall be located at each operator control station and at other locations where emergency stop is required and shall be positioned for easy access and for non-hazardous operation by the operator and others who may need to operate them.

Testing

Testing should be incremental and aim to credibly and quantitatively verify all functions of the emergency stops before the device is placed in the water and be done at all stages, including tests when the device is deployed and operating. On land, pre-deployment testing should include separate activation of each and every safety stop and direct verification that all mechanical and electrical actions have occurred. This needs to occur again when the device is placed in the water and once the MEC is on station operating. After activation of each safety stop, the device should be brought back up to full operation before the next stop is tried.
Emergency stops are also used to provide impulsive type loads for open-water structural testing.