Chemical Facility - Flood Risk Assessment

The recent flooding of chemical facilities in Houston and resultant release of hazardous materials is a cause of concern to anyone charged with protecting the environment.  This prompted me to wonder whether enough attention has been paid in Ireland to flood risk assessment of such facilities.

The impact of floods on chemical and pharmaceutical facilities obviously depends on factors such as height of flood waters, whether there is a surge (perhaps due to sudden release of flood waters), whether there has been an orderly shutdown of the facility and so on.  The storm at Houston was predicted and facilities shut down operations, but there was still a release of hazardous materials.  

In the case of some facilities in Houston, storage tanks collapsed and backup electricity generators failed.  Storage tanks are liable to float or become unstable when containment bunds are flooded, especially if the tanks are only part full.  Some tanks need their contents cooled and therefore rely on refrigeration plants to provide cooling.  If the flooding knocks out electricity supplies and the backup generators, then tank contents may become unstable.

The EPA in Ireland requires licensed sites to carry out flood risk assessment in order to prepare accident prevention procedures and emergency response plans.  The published guidance requires a risk assessment to ensure all potential emergency situations are addressed.  Examples in the guide are given of potential emergency situations and flooding is included.  One can imagine that the US EPA would have had similar requirements for accident prevention and yet an environmental disaster has occurred.

Flooding events are becoming more common and severe, witness the recent flooding in the northwest of Ireland.  Events once considered to be one in a hundred years are now perhaps much more frequent.  It would therefore be prudent to consider flooding more seriously and the consequences on storage of chemicals in drums and tanks.

The secondary containment around storage tanks and drums is designed to retain the contents in the event of a leak.  However, the design of many such containment facilities may offer little protection from flood water.  Bund walls are often limited to 1.5 m high so as not to impede access but many walls are lower.  Some bunds, such as for drum store facilities, have no walls and reply of a channel around the bund leading to a sump.  This arrangement allows for easy access for fork trucks but leaves the drums and tanks vulnerable to be washed away by flood waters.

Standby generators are often in shipping containers and located at ground level. These too can be overwhelmed by flood water.

A prudent flood risk assessment therefore needs to be made of the likely height of flood water and a determination made as to whether secondary containment systems and backup generators are sufficiently robust to withstand such events.


The author, Bob Sutcliffe, is a director of Environmental Efficiency, a consultancy dedicated to helping clients maintain environmental compliance and embrace best practice.  The views expressed are the author’s.