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Hazard assessment

Chemical Hazard and Risk Management (CHARM)

The OCNS conducts hazard assessments on chemical products that are used offshore.

The CHARM model calculates the ratio of Predicted Effect Concentration against No Effect Concentration (PEC:NEC). This is expressed as a Hazard Quotient (HQ), which is then used to rank the product.

The HQ is converted to a colour banding, illustrated in Table 1, which is then published on the Definitive Ranked Lists of Registered Products, Excel format (ZIP, 418.31 KB, updated 22 April 2015) .

Data used in the CHARM assessment include toxicity, biodegradation and bioaccumulation.

The CHARM model is divided into four main algorithms:

  • production
  • completion/work-over
  • drilling
  • cementing.

Table 1: OCNS HQ and colour bands 

Minimum HQ value Maximum HQ value Colour banding
>0 <1 Gold

 Lowest hazard
OCNS Down Arrow Highest hazard

≥1 <30 Silver
≥30 <100 White
≥100 <300 Blue
≥300 <1000 Orange
≥1000   Purple


Products not applicable to the CHARM model (i.e. inorganic substances, hydraulic fluids or chemicals used only in pipelines) are assigned an OCNS grouping, A - E. Group A includes products considered to have the greatest potential environmental hazard and Group E the least (see Tables 2 and 3 below).

Each individual substance in an offshore chemical is ranked by applying the OCNS ranking scheme. The overall ranking is determined by that substance having the worst case OCNS ranking scheme assignment. The method of assignment of the OCNS letter grouping is described below.

The way in which each OCNS group letter is assigned can be seen in more detail here:

The initial group is determined using Table 2. All submitted toxicity data for the product are compared against the table. The value giving the worst case "initial grouping" (i.e. the test giving the most toxic response) is used as the initial Group for the substance. 

Table 2: Initial OCNS grouping

Initial grouping






Result for aquatic-toxicity data (ppm)






Result for sediment-toxicity data (ppm)






  • Aquatic toxicity refers to the Skeletonema costatum EC50, Acartia tonsa LC50, and Scophthalmus maximus (juvenile turbot) LC50 toxicity tests.
  • Sediment toxicity refers to the Corophium volutator LC50 test.

The final grouping is determined using Table 3 as a guide. Select the column that applies to the candidate product and adjust the initial Group accordingly. If the classification should theoretically move beyond Group A or E, the product will nevertheless be assigned to that particular Group.

Table 3: Adjustment criteria for OCNS grouping

Increase by 2 groups (e.g. from C to E) Increase by 1 group (e.g. from C to D) Do not adjust initial grouping Decrease by 1 group (e.g. from C to B) Decrease by 2 groups (e.g. from C to A)
Substance is readily biodegradable and is non-bioaccumulative Substance is inherently biodegradable and is non-bioaccumulative Substance is not biodegradable and is non-bioaccumulative
Substance is inherently biodegradable and bioaccumulates Substance does not biodegrade and bioaccumulates
    Substance is readily biodegradable and bioaccumulates    

Definitions of terms used in the classification table

  • Readily biodegradable: results of >60% biodegradation in 28 days to an OSPAR HOCNF accepted ready biodegradation protocol
  • Inherently biodegradable: results of >20% and <60% to an OSPAR HOCNF accepted ready biodegradation protocol or result of >20% by OSPAR accepted Inherent biodegradation study
  • Not biodegradable: results from OSPAR HOCNF accepted ready biodegradation protocol or inherent biodegradation protocol are <20%, or half-life values derived from aquatic simulation tests indicate persistence
  • Non-bioaccumulative: Log Pow <3, or BCF ≤100 and the molecular weight is ≥700
  • Bioaccumulative: Log Pow ≥3, or BCF >100 and the molecular weight is <700, or if the conclusion of a weight-of-evidence expert judgement under OSPAR Agreement 2008-5 is negative
  • Aquatic toxicity test result: LC50/EC50 data for Skeletonema costatum, Acartia tonsa or Scophthalmus maximus (juvenile turbot) (units = ppm or mg/litre)
  • Sediment toxicity test result: LC50 data for Corophium volutator (units = ppm or mg/kg).

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Last Modified: 27 April 2014