SQLAlchemy, Flask and cross-contamination?

I have taken over a flask app, but it does not use the flask-sqlalchemy plugin. I am having a hard time wrapping my head around how it's set up.

It has a database.py file.

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker, scoped_session, Session


_session_factory = None
_scoped_session_cls = None
_db_session: Session = None


def _get_session_factory():
    global _session_factory
    if _session_factory is None:
        _session_factory = sessionmaker(
            bind=create_engine(CONNECTION_URL)
        )
    return _session_factory


def new_session():
    session_factory = _get_session_factory()
    return session_factory()


def new_scoped_session():
    global _scoped_session_cls
    if _scoped_session_cls is None:
        session_factory = _get_session_factory()
        if not session_factory:
            return
        _scoped_session_cls = scoped_session(session_factory)
    return _scoped_session_cls()


def init_session():
    global _db_session

    if _db_session is not None:
        log.warning("already init")
    else:
        _db_session = new_scoped_session()
    return _db_session


def get_session():
    return _db_session

We we start up the flask app, it calls database.init_session() and then anytime we want to use the database it calls database.get_session().

Is this a correct/safe way to interact with the database? What happens if there are two requests being processed at the same time by different threads? Will this result in cross-contamination with both using the same session

from SQLAlchemy, Flask and cross-contamination?