Communications provider KCOM has been fined £900,000 after flooding caused by Storm Eva led to the failure of 74 emergency calls.
Ofcom found “serious weaknesses” in the Hull-based firm’s emergency call service which meant people in the area could not make calls to 999 or 112.
The regulator found it had broken rules to ensure people can contact emergency services at all times.
KCOM operates the main telephone and broadband network in Hull.
It is the only UK city not served by BT’s Openreach, which controls the telecoms network.
Ofcom said KCOM notified the regulator on 28 December 2015 that its emergency call service for the Hull area had failed for around four hours.
It said the failure was because of flooding at one of the BT’s telephone exchanges in York in the wake of Storm Eva.
However, Ofcom found that all emergency calls from customers in that area relied on the flooded telephone exchange in York.
Under Ofcom rules, the telephone and broadband operator should have been able to automatically divert emergency calls via back-up routes.
The investigation found that although the firm did have back-up routes in place, these also relied on the flooded telephone exchange in York.
Ofcom said KCOM created an alternative route to carry emergency calls that bypassed the flooded telephone exchange in York within two hours of identifying the problem.
The regulator said it expected telephone companies’ services to be resilient enough “to the greatest extent possible” to connect emergency calls at all times, even in challenging circumstances.