By law (FAA regulations), all intentional parachute jumps must be made with a single harness, dual parachute system with both a main canopy AND a reserve canopy. In other words, you have a second (or spare) canopy in case the first one fails to open properly.
However, it must be noted that the technology utilized in today's sport parachuting equipment is light years ahead of the old military surplus gear used in the '60s and '70s. The canopies are drastically different from the classic G.I. Joe round parachutes. The materials are stronger, lighter and last longer, the packing procedures are simpler, the deployment sequence is much more refined, etc.
The reserve canopies are even more carefully designed and packed. The reserve parachute must be inspected and repacked every 120 days by an FAA rated parachute Rigger - even if it has not been used during that time.
The student's main canopy is always packed either by a rigger or under a rigger's direct supervision by experienced packers.
There are also additional safety features employed to ensure canopy deployment such as Automatic Activation Devices (AAD) and Reserve Static Lines (RSL) which add still more layers of safety.
Skydiving is a high-speed aerial sport that exposes its participants to the real risk of injury and death. Each year in the U.S. about 35 people die while making approximately 2 million parachute jumps. Other skydivers are sometimes killed while riding aboard jump aircraft.
Analysis of skydiving accidents show that most are caused by jumpers
who make mistakes of procedure or judgment. Contrary to popular belief, very few skydiving
accidents or injuries are caused by random equipment failure.
Those skydivers who are trained well, who stay current and who take a conservative approach to the sport are involved in very few accidents and suffer few -- if any -- injuries.
Some people prefer not to expose themselves to significant risks, while others accept the risk in exchange for the enjoyment the activity offers.
Most parachute centers require that each customer sign a legally
binding assumption-of-risk agreement. The document makes it clear that the sport has its
risks and that the jumper is electing to jump in spite of those risks.
Safety and risk are not the same things. Risk is measured. Safety is judged. Safety is the personal or societal acceptance of a given risk.
Risk is a measured quantity. Risk is the product of the probability of something happening and the severity of harm when it does happen. Risk equals "how often" times "how bad". Probabilities can be divided into 5 categories: Frequent, Probable, Occasional, Remote and Improbable. Severity can be divided into 4 categories: Catastrophic, Critical, Marginal and Negligible. Risk is then given as "Frequent-Negligible" for rubber bands breaking or "Remote-Catastrophic" for a double malfunction. Most malfunctions will have a risk of "Occasional-Catastrophic" or "Occasional-Critical" depending on how survivable landing the malfunction would be.
All events in skydiving could be assigned some risk value, based on the definition just given. The risk value should be based on data collected over many years or test drops. In essence, the risk value for an event should be based on a large set of measurements and observations. Unfortunately, this is not always the case.
Risks are higher for events that have a dreaded result or catastrophic consequence. Risks in sports and occupations that have fatalities are higher than sports and occupations that don't generally have fatalities. (Cowboys have riskier jobs than secretaries.)
Maturity of a technology affects risk perceptions, too. Nuclear power plants have higher risks than coal-powered plants because so much more is known about burning coal than nuclear energy.
System complexity will increase risks. Complex systems are harder to understand. They fail in complex ways. Sometimes a failed or degraded system is difficult to detect. The more complex a system is the more important it becomes to understand the system, how it works, how it fails and learn preventative and corrective actions.
Effective risk assessment and risk reduction comes from understanding parachute systems, knowing the proper roles of the controls, recognizing degrading system performance and having preventive and corrective plans.