Tesla coil equipment produces large quantities of ozone, which is poisonous. Adequate ventilation must always be maintained. Spark gaps used in Tesla equipment produce intense ultraviolet light. This light can burn the retina of the eye with ease. Always cover any exposed arcs.
Tesla coils can and have started a number of fires.
They can arc to flammable objects with ease. Any fire extinguishing equipment must be rated for electrical fires but still must only be used when the power is removed from this type of extremely high voltage equipment. These substances can cause very serious and long-term heath problems and fatal cancers. Components used in Tesla coils can explode with great violence. High voltage capacitors especially can store a tremendous amount of energy and can fail catastrophically.