You don't want tenants to get injured (or claim injury) and sue you.

My friend suffered serious injuries (the guy who hit him was fine of course), and was taken by ambulance to the hospital. 

Given national news over the years concerning injury and even many deaths resulting from defective decks you'd be wise to handle this situation promptly. 

If the tenant reaches for the fire extinguisher you supplied and it does not work for any reason (including it losing its charge because they kept it too long) and they suffer a loss or injury they can sue you for supplying faulty equipment.

Liability insurance will cover many things the contractor may accidentally do to cause damage to property or people in the course of his work; workers comp will cover personal injury of the worker and/or his employees/sub-contractors.

That is not accurate. 99.9% of the personal injury attorneys are chasing the insurance money not your personal assets and as it's an easier form of collection.

I am 24 years old, just graduated, and I recently settled in personal injury lawsuit and will be walking away with around $20,000 in my pocket. 

Following any advice may result in injury, divorce, felony charges, civil litigation or death.You shouldn't randomly call people as it is a huge waste of time and will result in sitting in a warm bath with a razor blade before the first lead ever shows up.  

Johnny Gets injured in a ski accident and has to take time off of work insurance pays 80% of accident but he is left with a 4000 dollar bill he must pay and Johny cant work for 3 months because of the injury cannot make car pmt.

I owned a PM company in Belize, and the first part of my PM contract said,"Owner agrees with the exception of fraud, theft or any other act that is a crime in the country of Belize, Owner agrees to indemnify, defend, and hold harmless Manager and all persons in Manager’s firm, regardless of responsibility, from all costs, expenses, suits, liabilities, damages, attorney’s fees, and claims of every type, including but not limited to, those arising out of injury or death of any person, employee, tenant or guest upon the premises or damage to any real or personal property of any person, employee, tenant, or guest upon the premises, including Owner, in any way relating to the management, rental, security deposits, or operations of the Premises by Manager, or any person in Manager’s firm, or the performance or exercise of any of the duties, powers, or authorities granted to the Manager.