TNC Pipeline Negligence Lawsuit: Elements of Negligence, Tests, and Defenses

TNC Pipelines owns an oil pipeline running from Fort McMurray to a refinery in Medicine Hat. The pipeline is brand new and complies with all the latest safety and environmental regulations. One of these regulations requires regular emergency shut-off valves that stops the flow oil through the pipeline if a sudden depressurisation is detected, indicating a rupture, in order to minimise the amount of oil spilled in the event of the rupture.
The emergency shut-off valves are placed at regular intervals along the length of the pipeline and must be inspected regularly. A small set of stairs from the ground leads up to a control room at each valve site. TNC opted to build the stairs out of wood. Wood was cheaper and easier to maintain compared to steal.
Aaron is a site operator and an employee for TNC. One of his jobs is to ensure TNC sites are safe for personnel. One day, while climbing the stairs to an emergency shut-off valve control room, he notices one of the wooden steps is partially rotted. When he places his weight on it, there is a noticeable cracking sound and the step sags, but does not break. Aaron continues to the control room and performs his regular inspection to ensure the emergency shut-off systems are functioning properly. On his way back down the steps, the partially rotten step cracks again, even louder this time, and sags even more than it did before, but still holds his weight. Aaron only weights 60kg, but knows a lot of other people in his line of work weigh well over 90kg. Aaron calls his supervisor and tells him about the rotten step. The supervisor tells Aaron not to bother with it because it'll mean working overtime and their maintenance budget is already stretched thin.
"Don't replace the step until it's completely rotted through. If it supported you, it'll support someone else." His supervisor tells him. Aaron then leaves the site. A few days later, Ivan, another TNC employee, goes to the same site. TNC is running a safety drill to train employees in proper procedures in the event the pipeline bursts and causes and oil spill. On his way up the stairs, Ivan doesn't see the partially rotten step. Ivan is much bigger than Aaron, weighing 92kg, and the step gives way when he steps on it. Ivan falls four metres to the ground below, breaking his leg and three ribs.
 Ivan is unable to work for three months due to his broken leg and his broken ribs cause him severe pain. To make matters worse, due to a struggling economy, increasing budget deficits, and pressure from industry, the Provincial Government scrapped the Alberta Worker's Compensation Board (WCB), which means Ivan now has to sue TNC in order to obtain compensation. Ivan sues TNC under the law of negligence.

Your task is as follows:
1) List the elements of negligence.
2) Describe what must be shown in order to show that each element is satisfied (ie, what test is applied?
3) Apply the elements of negligence to this fact scenario to determine if each element is satisfied. 
4) Discuss whether any defences apply to this fact scenario. Explain why each defence will or will not succeed.
5) State a conclusion on whether TNC will be liable for Ivan's injuries and losses.