Technical Article

Non-Hazardous Substance Clean-up

Lately the Fire Service has become very disciplined in not flushing hazardous substances and fuel spillage’s into the stormwater system, but what about spillage’s of not so hazardous substances that may appear to be relatively innocuous and harmless?

The environmental concerns can be significant if liquid consumables are allowed to enter a watercourse, pond or stream as these will have an adverse affect on the aquatic environment.

The issue in this particular instance is the Biological Oxygen Demand (BOD). BOD is the measure of oxygen required over a few days to break down the product.


Liquid sugar for example has a Biological Oxygen Demand (BOD) of approx. 780,000 mg/l.     i.e. 780,000 mg of oxygen are used up per litre of liquid sugar.


A liquid sugar spill of around 70 litres =780,000 x 70 mg of oxygen required in the breakdown process (54600000 mg of Oxygen).

In lay mans terms this means that during the breakdown of liquid sugar in the natural environment it would use up all the oxygen 5460000 litres of water. (Taken that the dissolved oxygen is in good quality water at about 10mg/l).

For aquatic life (fish etc) to survive, the oxygen level should not fall much below a life sustaining value of 4mg/l of oxygen (at this level it could barely support life). This therefore increases the volume of water which could be seriously impacted during the breakdown process of the 70 litres of Liquid sugar to = 11000000 litres.

All food type products have an oxygen demand on the aquatic environment and should not be allowed to be washed into the stormwater system (and ultimately into the local streams, rivers) where it will seriously reduce the capacity for supporting aquatic life.

Further examples, milk has a BOD of approximately 102,500 mg/l, Pepsi cola 79,500 mg/l, fanta orange 84,300 mg/l, fish wastes 112,000 mg/l, beer 445 mg/l and raw sewage entering the treatment plant typically 350 mg/l

Clean-up operations could be conducted using a commercial ‘sucker-truck’ or alternatively flushing the spillage into a cesspit or similar and then pumping into the sewer system for treatment (check with TLA for significant spills) or onto a grassed area away from a watercourse or natural waterway. This would then allow breakdown to occur in the soil. (This should be avoided in the case of milk due to the probable odour associated with curdling). 

This obviously highlights the need to NOT flush any substance, not matter how harmless it may appear, into stormwater system.

Other low hazard products, which can have toxic effects directly or indirectly on aquatic life, include:

  • Detergents: Directly toxic to aquatic life and deoxygenate water

  • Silt & Sand: Smothering and choking of aquatic life

  • Pesticides: Directly toxic to aquatic life and deoxygenate water

  • Paints/Dyes: Deoxygenating, photosynthesis reduction, light absorption.

  • Fertilisers: Directly toxic to aquatic life and deoxygenate water

  • Firewater run-off: May be toxic depending on size/scale of incident

New Zealand Fire Brigades Institute