Somewhat 30 years ago, I worked in a laboratory of a US chemical company. One day a worker put back unused hydrogen peroxide mistakenly into the a drum of Hydrochloric acid. Chlorine evolved with the following reaction.
H2O2 + 2HCl -> 2 H2O + Cl2
I felt the choking gas, switched on all ventilation, closed doors of source room. And got an extra holiday without the need to work.
There was another experience at the age about ten or little more. Then I was small and Christmas tree was tall.
I used to play alone without toys due to proverty of my family. Once I played with electrolysis of high concentration salt water from kitchen with a dry cell. I choked by the chlorine gas seriously from electrode and dare not play it again.
From these points, little chlorine is a relatively safe poisonous gas in open area.
However it could be fatal in a poorly ventilated space. I ever saw a news about a worker used hydrochloric acid to clean toilet blow and then poured bleaching solution into it. He was then poisoned seriously and sent to hospital.
The chemical reaction to generate chlorine is like this.
NaClO + 2HCl -> Cl2 + NaCl + H2O
As all these are easily accessible in household, take precaution from never mixing them up.