If those fumes are released in a plenum space, they can spread throughout the building through the air circulation system.
In 2007, a development program specifically targeting the production of a non-halogen plenum cable compound was announced to specifically address lingering toxicity concerns presented by halogenated compounds for use in European and other global markets.
Typically this results in reduced flexibility of plastic cables, making it stiff and hard to bend.
The videos here, while presenting a comparative viewpoint, do not show the fire tests used to determine the relative acceptability of cables for use in plenum spaces.
The fire tests shown in the referenced link are small scale (bench) demonstrations of relative burning characteristics under one condition that is not sanctioned by or used by any safety code or regulation in determining suitability for use in plenum or other applications.