The lead ministry is Municipal Affairs & Housing. The requirements of Ontario's Provincial Policy Statement (PPS) are not optional: Section 3 of the Planning Act requires that planning decisions "shall be consistent with" policy statements issued under the Act. In other words, decisions made by municipalities and other decision-making bodies must comply with PPS requirements.

The Policy section of the PPS is extensive, clear and internally consistent. Section 3.0 specifically addresses the need to protect public health and safety and provides the following prescriptive statement: 
"Development shall be directed away from areas of natural or human-made hazards where there is an unacceptable risk to public health or safety or of property damage, and not create new or aggravate existing hazards" (p. 30).

The only questions would be:
- are transmission pipelines human-made hazards?
- do they present an unacceptable risk to public safety?
- do they present an unacceptable risk re. 
[TBC]