What is the difference between ordinary risk assessment, Qualitative Risk assessment, and Quantitative risk assessment?

In our life we make all the time risk assessments, 

When we pass the road, we make a risk assessment and we check the both side of the road,

When we drive our car, we check the fuel, water and air pressure of the tires.

All these risk assessments and other we make without any ranking of the risk, is ordinary risk assessment. And if you are not good in the ordinary risk assessment, you will not live long!

Qualitative Risk Assessment:

It is ranked as urgency or importance i.e. Very high, high, low, very low etc.

As different persons have different knowledge, abilities, risk perceptions and trainings so different person may rank the same risk on different ranks. For example, a cable tray with live electricity, in the way, may present very high risk according to me and another person rank it as a low!!

Quantitative Risk Assessment:

In this risk assessment, the risk is divided into likelihood and severity and ranked numerically i.e.1 to5.

Severity Scale

1

2

3

4

5

Likely injury

Minor injury or trauma not requiring hospital treatment

Non-immobilizing injury or trauma but requiring hospital treatment

Immobilizing injury or trauma requiring hospital treatment

Severe injury or trauma requiring urgent hospital treatment

Very severe life-threatening event

and a likelihood scale for a hazard occurrence:

Likelihood Scale

1

2

3

4

5

Hazard occurrence

Highly unlikely

Unlikely

Possible

Likely

Very likely

If the cable tray is there in the way and no person pass from that area and the cable is also insulated so the likelihood will be low i.e.1 or2. but if the person get in touch with direct electricity, the severity will be high i.e.3 or4. and risk will be calculated:

Risk = likelihood X severity

         =      2   X  4 

         =  8

There will be a chart from1 to25 to set the ranking of the risk to show if the risk is tolerable or need further steps to bring the ranking down in tolerable or safe conditions.

It is also possible to set risk priority number RPN by ranking the detection of the risk.

Risk = Likelihood X Severity X Detection

Same ranking is used from1 to5 for each unit i.e.5 X5 X5 =125