Risk assessment is used for uncertain events that could have many outcomes and for which there could be significant consequences.
In a qualitative assessment, probability and consequence are not numerically estimated, but are evaluated verbally using qualifiers like high likelihood, low likelihood, etc.
Qualitative assessments are good for screening level assessments when comparing/screening multiple alternatives or for when sufficient data is not available to support numerical probability or consequence estimates.
Once numbers are inserted into the analysis (either by quantifying the likelihood of a hazard or quantifying the consequences) the analysis transitions to a semi-quantitative or quantitative risk assessment.
Some of this subjectivity can be eliminated by developing rating scales that are agreed upon by the sponsor, project manager, and key team members.