## 4 Cybersafety Analysis
### Identify Unsafe/Insecure Control Actions
* Pump/Compressor Critical Speed and Reverse Rotation  
The compressor motor has certain critical speeds at which mechanical resonance can occur. Typically, the VFD is programmed to skip over these resonant frequencies [26]. However, operating the motor at its critical speed, can cause considerable damage to 'the bearings and the motor shaft' [27] [UCA-5]. Another unsafe condition for the compressor motor is reverse rotation; the VFD can be easily toggled to change the direction of rotation. Although reversing the direction of rotation would not change the direction of fluid flow through the compressor, it would cause significant damage to the compressor due to vibrations [UCA-4, UCA-5]. * Lubrication Oil  
A Centrifugal compressor needs oil forced around its internal components (such as gears, thrust bearings, etc.) to provide lubrication and remove heat caused by friction. The lubrication oil has to be at the correct temperature and pressure for it to perform its intended function; it must be thin enough to lubricate properly at high speeds of rotation but also thick enough to handle the heat and refrigerant contamination that can occur. If the lubrication oil conditions are not at the correct temperature and pressure, it can destroy the compressor in a matter of a few minutes because of the excessive build-up of heat through friction in the internal components [28] [UCA-6]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Action By** & **Control Action** & **Not Providing Causes** & **Providing Causes** & **Too Soon, Too Late**, & **Stopped too Soon**, \\  & **Control Action** & **Hazard** & **Hazard** & **Out of Order** & **Applied too Long** \\ \hline \hline \multirow{4}{*}{Start/Stop Equipment} & \multirow{4}{*}{Start/Stop Equipment} & UCA-1: Operator does not shut down & UCA-2: Operator bypasses safeties by forcing flags/overriding & UCA-3: Operator provides hazardous manual inputs via & UCA-4: Operator changes chiller controller mode to mutual and leaves it in manual inputs via & UCA-4: Operator changes chiller controller mode to mutual and leaves it in manual (for too long) when controller \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\ Plant Operator & \multirow{4}{*}{Security Controls} & UCA-1S: Operator does not report anomalous behaviour to & UCA-2S: Operator & & & \\  & & & & & downloads malicious & \\  & & & & & & \\  & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\ \hline \hline \multirow{4}{*}{Plant Management} & \multirow{4}{*}{Issue Policies/Funds} & UCA-1S: Management does not enforce an effective path/vulnerability & UCA-2S: Management produces to keep production running/during emergencies//duffinging & UCA-3S: Management changes into failure & does not follow its incident response plan \\  & & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\  & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._* Motor Burnout  
If a compressor motor is operating at its temperature or current limit, a command to increase motor speed would result in overheating; excessive heat can lead to premature loss of motor winding insulation, resulting in the motor burning itself out [UCA-1, UCA-8]. * Surging  
Another characteristic hazardous condition for centrifugal chillers is surging. This can occur when the compressor differential pressure exceeds design limits, particularly during low-load operation; it is caused when the required lift exceeds the systems pumping capacity. It may be caused by either increasing the condenser temperature and pressure or reducing the evaporator temperature and pressure--both could be caused by reducing water flowrate in the condenser or evaporator at low load conditions. Once surging occurs, the output pressure of the compressor is drastically reduced, resulting in flow reversal within the compressor.