Regulation 23 - Accidental oil outflow performance

.1	Load line draught (d_S) is the vertical distance, in metres, from the moulded baseline at mid-length to the waterline corresponding to the summer freeboard to be assigned to the ship. Calculations pertaining to this regulation should be based on draught d_S, notwithstanding assigned draughts that may exceed d_S, such as the tropical load line.
.2	Waterline (d_B) is the vertical distance, in metres, from the moulded baseline at mid-length to the waterline corresponding to 30% of the depth D_S.
.3	Breadth (B_S) is the greatest moulded breadth of the ship, in metres, at or below the deepest load line draught d_S.
.4	Breadth (B_B) is the greatest moulded breadth of the ship, in metres, at or below the waterline dB.
.5	Depth (D_S) is the moulded depth, in metres, measured at midlength to the upper deck at side.
.6	Length (L) and deadweight (DW) are as defined in regulations 1.19 and 1.23, respectively.

3 To provide adequate protection against oil pollution in the event of collision or stranding, the following shall be complied with:

.1	for oil tankers of 5,000 tonnes deadweight (DWT) and above, the mean oil outflow parameter shall be as follows:
		O_M ≤ 0.015		for C ≤ 200,000 m³
		O_M ≤ 0.012 + (0.003/200,000)(400,000 - C)
				for 200,000 m³ < C < 400,000 m³
		O_M ≤ 0.012		for C ≥ 400,000 m³

	for combination carriers between 5,000 tonnes deadweight (DWT) and 200,000 m³ capacity, the mean oil outflow parameter may be applied, provided calculations are submitted to the satisfaction of the Administration, demonstrating that, after accounting for its increased structural strength, the combination carrier has at least equivalent oil outflow performance to a standard double hull tanker of the same size having a O_M ≤ 0.015.
		O_M ≤ 0.021		for C ≤ 100,000 m³
		O_M ≤0.015 + (0.006/100,000)(200,000 - C)
				for 100,000 m³ < C ≤ 200,000 m³
	where:
	O_M = mean oil outflow parameter
	C = total volume of cargo oil, in m³, at 98% tank filling.
	.2	for oil tankers of less than 5,000 tonnes deadweight (DWT): The length of each cargo tank shall not exceed 10 m or one of the following values, whichever is the greater:
	.2.1	where no longitudinal bulkhead is provided inside the cargo tanks: but not to exceed 0.2L
	.2.2	where a centreline longitudinal bulkhead is provided inside the cargo tanks:
	.2.3	where two or more longitudinal bulkheads are provided inside the cargo tanks:
		.2.3.1	for wing cargo tanks: 0.2L
		.2.3.2	for centre cargo tanks:
			.2.3.2.1
			.2.3.2.2
			.2.3.2.2.1	where no centreline longitudinal bulkhead is provided:
			.2.3.2.2.2	where a centreline longitudinal bulkhead is provided:
	b_i is the minimum distance from the ship's side to the outer longitudinal bulkhead of the tank in question measured inboard at right angles to the centreline at the level corresponding to the assigned summer freeboard.

4 The following general assumptions shall apply when calculating the mean oil outflow parameter:

.1	The cargo block length extends between the forward and aft extremities of all tanks arranged for the carriage of cargo oil, including slop tanks.
.2	Where this regulation refers to cargo tanks, it shall be understood to include all cargo tanks, slop tanks and fuel tanks located within the cargo block length.
.3	The ship shall be assumed loaded to the load line draught d_S without trim or heel.
.4	All cargo oil tanks shall be assumed loaded to 98% of their volumetric capacity. The nominal density of the cargo oil (ρ_n) shall be calculated as follows: ρ_n = 1000(DWT)/C (kg/m³)
.5	For the purposes of these outflow calculations, the permeability of each space within the cargo block, including cargo tanks, ballast tanks and other non-oil spaces, shall be taken as 0.99, unless proven otherwise.
.6	Suction wells may be neglected in the determination of tank location provided that such wells are as small as practicable and the distance between the well bottom and bottom shell plating is not less than 0.5h, where h is the height as defined in regulation 19.3.2.

5 The following assumptions shall be used when combining the oil outflow parameters:

The mean oil outflow shall be calculated independently for side damage and for bottom damage and then combined into the non-dimensional oil outflow parameter O_M, as follows:

O_M = (0.4O_MS + 0.6O_MB)/C

where:

O_MS = mean outflow for side damage, in m^³; and

O_MB = mean outflow for bottom damage, in m^³.

For bottom damage, independent calculations for mean outflow shall be done for 0 m and minus 2.5 m tide conditions, and then combined as follows:

O_MB = 0.7O_MB(0) + 0.3O_MB(2.5)

where:

O_MB(0) = mean outflow for 0 m tide condition; and

O_MB(2.5) = mean outflow for minus 2.5 m tide condition, in m^³.

6 The mean outflow for side damage O_MS shall be calculated as follows:

where:

i	represents each cargo tank under consideration;
n =	total number of cargo tanks;
P_S(i) =	the probability of penetrating cargo tank i from side damage, calculated in accordance with paragraph 8.1 of this regulation;
O_S(i) =	i) = the outflow, in m³, from side damage to cargo tank i, which is assumed equal to the total volume in cargo tank i at 98% filling, unless it is proven through the application of the Guidelines referred to in regulation 19.5 that any significant cargo volume will be retained; and
C₃ =	P n 0.77 for ships having two longitudinal bulkheads inside the cargo tanks, provided these bulkheads are continuous over the cargo block and P_S(i) is developed in accordance with this regulation. C₃ equals 1.0 for all other ships or when P_S(i) is developed in accordance with paragraph 10 of this regulation.

7 The mean outflow for bottom damage shall be calculated for each tidal condition as follows:

.1	where:
	i	represents each cargo tank under consideration;
	n =	the total number of cargo tanks;
	P_B(i) =	the probability of penetrating cargo tank i from bottom damage, calculated in accordance with paragraph 9.1 of this regulation;
	O_B(i) =	the outflow from cargo tank i, in m³, calculated in accordance with paragraph 7.3 of this regulation; and
	C_DB(i) =	factor to account for oil capture as defined in paragraph 7.4 of this regulation
.2	where: i, n, P_B(i) and C_DB(i) = as defined in subparagraph .1 above; O_B(i) = the outflow from cargo tank i, in m³, after tidal change.
.3	The oil outflow O_B(i) for each cargo oil tank shall be calculated based on pressure-balance principles, in accordance with the following assumptions:
	.3.1	The ship shall be assumed stranded with zero trim and heel, with the stranded draught prior to tidal change equal to the load line draught d_S.
	.3.2	The cargo level after damage shall be calculated as follows: where:
		h_c =	the height of the cargo oil above Z_l, in metres;
		t_c =	the tidal change, in metres. Reductions in tide shall be expressed as negative values;
		Z_l =	the height of the lowest point in the cargo tank above baseline, in metres;
		ρ_s =	density of seawater, to be taken as 1025 kg/m³;
		p =	if an inert gas system is fitted, the normal overpressure, in kilopascals, to be taken as not less than 5 kPa; if an inert gas system is not fitted, the overpressure may be taken as 0;
		g =	the acceleration of gravity, to be taken as 9.81 m/s²; and
		ρ_n =	nominal density of cargo oil, calculated in accordance with paragraph 4.4 of this regulation.
	.3.3	For cargo tanks bounded by the bottom shell, unless proven otherwise, oil outflow O_B(i) shall be taken not less than 1% of the total volume of cargo oil loaded in cargo tank i, to account for initial exchange losses and dynamic effects due to current and waves.
.4	In the case of bottom damage, a portion from the outflow from a cargo tank may be captured by non-oil compartments. This effect is approximated by application of the factor C_DB(i) for each tank, which shall be taken as follows:
		C_DB(i) =	0.6 for cargo tanks bounded from below by non-oil compartments;
		C_DB(i) =	1.0 for cargo tanks bounded by the bottom shell.

8 The probability PS of breaching a compartment from side damage shall be calculated as follows:

P_S = P_SL P_SV P_ST

where:

P_SL = 1 - P_Sf - P_Sa =

probability the damage will extend into the longitudinal zone bounded by X_a and X_f;

P_SV = 1 - P_Su - P_Sl =

probability the damage will extend into the vertical zone bounded by Z_l and Z_u; and

P_ST = 1 - P_Sy =

probability the damage will extend transversely beyond the boundary defined by y.

P_Sa, P_Sf, P_Sl, P_Su and P_Sy shall be determined by linear interpolation from the tables of probabilities for side damage provided in paragraph 8.3 of this regulation, where:

P_Sa =

the probability the damage will lie entirely aft of location X_a/L;

P_{Sf =}

the probability the damage will lie entirely forward of location X_f/L;

P_{Sl =}

the probability the damage will lie entirely below the tank;

P_{Su =}

the probability the damage will lie entirely above the tank; and

P_{Sy =}

the probability the damage will lie entirely outboard of the tank.

Compartment boundaries X_a, X_f, Z_l, Z_u and y shall be developed as follows:

X_a

the longitudinal distance from the aft terminal of L to the aftmost point on the compartment being considered, in metres;

X_f

the longitudinal distance from the aft terminal of L to the foremost point on the compartment being considered, in metres;

Z_l

the vertical distance from the moulded baseline to the lowest point on the compartment being considered, in metres;

Z_u

the vertical distance from the moulded baseline to the highest point on the compartment being considered, in metres. Z_u is not to be taken greater than D_S; and

the minimum horizontal distance measured at right angles to the centreline between the compartment under consideration and the side shell, in metres;*

Tables of probabilities for side damage

X_a/L	P_Sa
0.00	0.000
0.05	0.023
0.10	0.068
0.15	0.117
0.20	0.167
0.25	0.217
0.30	0.267
0.35	0.317
0.40	0.367
0.45	0.417
0.50	0.467
0.55	0.517
0.60	0.567
0.65	0.617
0.70	0.667
0.75	0.717
0.80	0.767
0.85	0.817
0.90	0.867
0.95	0.917
1.00	0.967

X_f/L	P_Sf
0.00	0.967
0.05	0.917
0.10	0.867
0.15	0.817
0.20	0.767
0.25	0.717
0.30	0.667
0.35	0.617
0.40	0.567
0.45	0.517
0.50	0.467
0.55	0.417
0.60	0.367
0.65	0.317
0.70	0.267
0.75	0.217
0.80	0.167
0.85	0.117
0.90	0.068
0.95	0.023
1.00	0.000

Z_l/D_S	P_Sl
0.00	0.000
0.05	0.000
0.10	0.001
0.15	0.003
0.20	0.007
0.25	0.013
0.30	0.021
0.35	0.034
0.40	0.055
0.45	0.085
0.50	0.123
0.55	0.172
0.60	0.226
0.65	0.285
0.70	0.347
0.75	0.413
0.80	0.482
0.85	0.553
0.90	0.626
0.95	0.700
1.00	0.775

Z_u/D_S	P_Su
0.00	0.968
0.05	0.952
0.10	0.931
0.15	0.905
0.20	0.873
0.25	0.836
0.30	0.789
0.35	0.733
0.40	0.670
0.45	0.599
0.50	0.525
0.55	0.452
0.60	0.383
0.65	0.317
0.70	0.255
0.75	0.197
0.80	0.143
0.85	0.092
0.90	0.046
0.95	0.013
1.00	0.000

P_Sy shall be calculated as follows:

P_Sy = (24.96 - 199.6y/B_S)(y/B_S) for y/B_S ≤ 0.05

P_Sy = 0.749 + {5 - 44.4(y/B_S - 0.05)}(y/B_S - 0.05)
for 0.05 < y/B_S < 0.1

P_Sy = 0.888 + 0.56(y/B_S - 0.1) for y/B_S ≥ 0.1

P_Sy shall not be taken greater than 1.

9 The probability P_B of breaching a compartment from bottom damage shall be calculated as follows:

P_B = P_BL P_BT P_BV

where:

P_BL = 1 - P_Bf - P_Ba =

probability the damage will extend into the longitudinal zone bounded by Xa and Xf;

P_BT = 1 - P_Bp - P_Bs =

probability the damage will extend into the transverse zone bounded by Yp and Ys; and

P_BV = 1 - P_Bz =

probability the damage will extend vertically above the boundary defined by z.

P_Ba, P_Bf, P_Bp, P_Bs, and P_Bz shall be determined by linear interpolation from the tables of probabilities for bottom damage provided in paragraph 9.3 of this regulation, where:

P_{Ba =}

the probability the damage will lie entirely aft of location X_a/L;

P_{Bf =}

the probability the damage will lie entirely forward of location X_f/L;

P_{Bp =}

the probability the damage will lie entirely to port of the tank;

P_{Bs =}

the probability the damage will lie entirely to starboard of the tank; and

P_{Bz =}

the probability the damage will lie entirely below the tank.

Compartment boundaries X_a, X_f, Y_p, Y_s, and z shall be developed as follows: X_a and X_f are as defined in paragraph 8.2 of this regulation;

Y_{p =}

the transverse distance from the port-most point on the compartment located at or below the waterline d_B, to a vertical plane located B_B/2 to starboard of the ship's centreline, in metres;

Y_{s =}

the transverse distance from the starboard-most point on the compartment located at or below the waterline d_B, to a vertical plane located B_B/2 to starboard of the ship's centreline, in metres; and

z =

the minimum value of z over the length of the compartment, where, at any given longitudinal location, z is the vertical distance from the lower point of the bottom shell at that longitudinal location to the lower point of the compartment at that longitudinal location, in metres.

Tables of probabilities for bottom damage

X_a/L	P_Ba
0.00	0.000
0.05	0.002
0.10	0.008
0.15	0.017
0.20	0.029
0.25	0.042
0.30	0.058
0.35	0.076
0.40	0.096
0.45	0.119
0.50	0.143
0.55	0.171
0.60	0.203
0.65	0.242
0.70	0.289
0.75	0.344
0.80	0.409
0.85	0.482
0.90	0.565
0.95	0.658
1.00	0.761

X_f/L	PBf
0.00	0.969
0.05	0.953
0.10	0.936
0.15	0.916
0.20	0.894
0.25	0.870
0.30	0.842
0.35	0.810
0.40	0.775
0.45	0.734
0.50	0.687
0.55	0.630
0.60	0.563
0.65	0.489
0.70	0.413
0.75	0.333
0.80	0.252
0.85	0.170
0.90	0.089
0.95	0.026
1.00	0.000

Y_p/B_B	P_Bp
0.00	0.844
0.05	0.794
0.10	0.744
0.15	0.694
0.20	0.644
0.25	0.594
0.30	0.544
0.35	0.494
0.40	0.444
0.45	0.394
0.50	0.344
0.55	0.297
0.60	0.253
0.65	0.211
0.70	0.171
0.75	0.133
0.80	0.097
0.85	0.063
0.90	0.032
0.95	0.009
1.00	0.000

Y_s/B_B	P_Bs
0.00	0.000
0.05	0.009
0.10	0.032
0.15	0.063
0.20	0.097
0.25	0.133
0.30	0.171
0.35	0.211
0.40	0.253
0.45	0.297
0.50	0.344
0.55	0.394
0.60	0.444
0.65	0.494
0.70	0.544
0.75	0.594
0.80	0.644
0.85	0.694
0.90	0.744
0.95	0.794
1.00	0.844

P_Bz shall be calculated as follows:

P_Bz = (14.5 - 67z/D_S)(z/D_S) for z/D_S ≤ 0.1,

P_Bz = 0.78 + 1.1(z/D_S - 0.1) for z/D_S > 0.1.

P_Bz shall not be taken greater than 1.

10 This regulation uses a simplified probabilistic approach where a summation is carried out over the contributions to the mean outflow from each cargo tank. For certain designs, such as those characterized by the occurrence of steps/recesses in bulkheads/decks and for sloping bulkheads and/or a pronounced hull curvature, more rigorous calculations may be appropriate. In such cases one of the following calculation procedures may be applied:

.1	The probabilities referred to in 8 and 9 above may be calculated with more precision through application of hypothetical subcompartments.†
.2	The probabilities referred to in 8 and 9 above may be calculated through direct application of the probability density functions contained in the Guidelines referred to in regulation 19.5.
.3	The oil outflow performance may be evaluated in accordance with the method described in the Guidelines referred to in regulation 19.5.

11 The following provisions regarding piping arrangements shall apply:

Lines of piping that run through cargo tanks in a position less than 0.30BS from the ship's side or less than 0.30D_S from the ship's bottom shall be fitted with valves or similar closing devices at the point at which they open into any cargo tank. These valves shall be kept closed at sea at any time when the tanks contain cargo oil, except that they may be opened only for cargo transfer needed for essential cargo operations.

Credit for reducing oil outflow through the use of an emergency rapid cargo transfer system or other system arranged to mitigate oil outflow in the event of an accident may be taken into account only after the effectiveness and safety aspects of the system are approved by the Organization. Submittal for approval shall be made in accordance with the provisions of the Guidelines referred to in regulation 19.5.

* For symmetrical tank arrangements, damages are considered for one side of the ship only, in which case all ''y'' dimensions are to be measured from that same side. For asymmetrical arrangements, reference is made to the Explanatory Notes on matters related to the accidental oil outflow performance, adopted by the Organization by resolution MEPC.122(52).

† Reference is made to the Explanatory Notes on matters related to the accidental oil outflow performance, adopted by the Organization by resolution MEPC.122(52), as amended.