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WEIGHTING OF CHEMICALS
To assess and compare the significance of the use and discharge of chemicals in the EBT, it is necessary to express the environmental hazard of different chemicals in a single unit of measurement. To achieve this for the chemicals used by the UK offshore industry, a method has been developed to add chemicals from different environmental hazard categories together. The method is based on the assumption that the various groups into which these chemicals are categorized reflect their hazard to the environment.
Two methods are currently used to categorize chemicals used by the offshore oil and gas industry. The preferred method is the CHARM model (Chemical Hazard Assessment and Risk Management). Chemicals that cannot be assessed by this model are categorized in the grouping system from the Revised Offshore Chemicals Notification Scheme (OCNS) that pre-dated the introduction of the (Harmonized Mandatory Control System (HMCS). See the OCNS page on the CEFAS web site for details.
Under the revised OCNS, chemicals were classified into groups with associated tonnage triggers. Production chemicals and drilling chemicals had different tonnage triggers (see Table).
OCNS Category/Group
Tonnage triggers for production chemicals
Tonnage triggers for drilling chemicals
4/A
40 tonnes
All proposed usage to be notified
3/B
70 tonnes
3 tonnes
2/C
150 tonnes
15 tonnes
1/D
375 tonnes
350 tonnes
0/E
1000 tonnes
4,750 tonnes
Production chemicals: The tonnage trigger for Group A chemicals is 40 tonnes, whereas the tonnage trigger for Group C chemicals is 150 tonnes. The method used in the EBT expresses Group C chemicals as Group A chemicals by multiplying the amounts of Group C chemical by 40/70 before adding them to a total ‘weighted' figure. Chemicals from other Groups are treated similarly.
Drilling chemicals: The tonnage trigger for Group B chemicals is 3 tonnes, whereas the Tonnage Trigger for Group C chemicals is 15 tonnes. The method expresses Group C chemicals as Group A chemicals by multiplying the amounts of Group C chemicals by 1/15 before adding them to a total ‘weighted' figure. In the absence of further guidance, the tonnage trigger for Group A chemicals of “any proposed usage” is taken to mean 1 tonne. Chemicals from other Groups are treated similarly.
With the introduction of the CHARM model, the EBT method was revised by one that also expressed the CHARMed chemicals as OCNS Group A equivalents. In the new method, chemicals with a Gold banding are considered as toxic as OCNS category E chemicals, and the shift in HQ ranges is used to calculate ‘tonnage triggers' for the other HQ ranges.
HQ range
Color banding
Tonnage triggers for calculation purposes only
Production chemicals
Drilling chemicals
0 = HQ < 1
Gold
1,000
4,750
1 = HQ < 30
Silver
33
142.5
30 = HQ < 100
White
10
47.5
100 = HQ < 300
Blue
3.3
14.25
300 = HQ < 1,000
Orange
1
4.75
1,000 = HQ
Purple
0.33
1.425
Performance indicators
