373 



The derivation of the figures given in table 1 is explained by Porricelli, Keith, 

 and Storch ^ on a topic-by-topic basis. The following paragraphs summarize the 

 information that pertains specifically to tankers and tank barges. 



Tankers and tank barges contribute to the oil pollution of the marine environ- 

 ment in four main ways : 



(1) Routine tank cleaning operations ; 



(2) Vessel casualties ; 



(3) Discharges from bilge pumping and leaking ; and 



(4) Spills during cargo handling oi)erations. 



A more comprehensive picture of the oil pollution associated with tankers is 

 depicted in figure 1. The relative magnitude of the four major categories is 

 shown on table 3. 



Intentional (routine) Discharges 



Of the 1.46 million metric tons of oil loss per year for which tankers 

 (including tank barges) are accountable (table 1), 967,()00 metric tons come from 

 routine ballasting and cleaning of cargo oil tanks. The following description of 

 these operations explains their purpo.se and the procedures involved. It should 

 be noted in advance that the oily ballast or oil residue involved in these operations 

 can be held on board ship and discharged into a ballast reception facility on 

 shore at the loading port if such a facility is available. 



LIABLE 1.— ESTIMATED ANNUAL OIL POLLUTION OF THE OCEANS 



Metric tons Percent 



Marine operations: 



Tankers: 



LOT (load-on-top) tank cleaning operations 265, 000 



Non-LOT tank cleaning operations 702,000 



Discharge due to bilge pumping, leaks and bunkering spills 100, 000 



Vessel casualties 250,000 



Terminal operations 70,000 



Tank barges: 



Discharge due to leaks 20,000 



Barge casualties 32,000 



Terminal operations... 18,000 



All other vessels: 



Discharge due to bilge pumping, leaks and bunkering spills 600,000 



Vessel casualties 250,000 



Offshore operations 100,000 



Nonmarine operations: 



Refineries and petrochemical plants 300, 000 



Industrial machinery 750,000 



Highway machinery _ 1,440,000 29.41 



Total 4,897,000 100.00 



Source: From Porricelli, Keith, & Storch, 1971. 



' J. D. Porricelli. V. F. Keith, R. L. Storch, "Tankers and the Ecologv," paper presented 

 to the Society of Naval Architects and Marine Enj?lneers, New Yorlc, N.Y., November, 1971. 



