Index: Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Data/HeightStructuresfailureMechanismSection2aAssessmentResultExtensions.cs
===================================================================
diff -u
--- Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Data/HeightStructuresfailureMechanismSection2aAssessmentResultExtensions.cs	(revision 0)
+++ Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Data/HeightStructuresfailureMechanismSection2aAssessmentResultExtensions.cs	(revision 4c8e08fbec305b763ae716ae7a3660d75c4c7b99)
@@ -0,0 +1,74 @@
+// Copyright (C) Stichting Deltares 2017. All rights reserved.
+//
+// This file is part of Ringtoets.
+//
+// Ringtoets is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+//
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using System;
+using Ringtoets.Common.Data.AssessmentSection;
+using Ringtoets.Common.Data.Probability;
+using Ringtoets.Common.Data.Structures;
+
+namespace Ringtoets.HeightStructures.Data
+{
+    /// <summary>
+    /// Extension methods for obtaining level 2a results from output for an assessment of the 
+    /// height structures failure mechanism.
+    /// </summary>
+    public static class HeightStructuresFailureMechanismSection2aAssessmentResultExtensions
+    {
+        /// <summary>
+        /// Gets the value for the detailed assessment of safety per failure mechanism section as a probability.
+        /// </summary>
+        /// <param name="sectionResult">The section result to get the assessment layer 2A for.</param>
+        /// <param name="failureMechanism">The failure mechanism the calculations belong to.</param>
+        /// <param name="assessmentSection">The assessment section the calculations belong to.</param>
+        /// <returns>The calculated assessment layer 2A; or <see cref="double.NaN"/> when there is no
+        /// calculation assigned to the section result or the calculation is not performed.</returns>
+        /// <exception cref="ArgumentNullException">Thrown when any parameter is <c>null</c>.</exception>
+        public static double GetAssessmentLayerTwoA(this StructuresFailureMechanismSectionResult<HeightStructuresInput> sectionResult,
+                                                    HeightStructuresFailureMechanism failureMechanism,
+                                                    IAssessmentSection assessmentSection)
+        {
+            if (sectionResult == null)
+            {
+                throw new ArgumentNullException(nameof(sectionResult));
+            }
+
+            if (failureMechanism == null)
+            {
+                throw new ArgumentNullException(nameof(failureMechanism));
+            }
+
+            if (assessmentSection == null)
+            {
+                throw new ArgumentNullException(nameof(assessmentSection));
+            }
+
+            if (sectionResult.Calculation == null || !sectionResult.Calculation.HasOutput)
+            {
+                return double.NaN;
+            }
+
+            ProbabilityAssessmentOutput derivedOutput = HeightStructuresProbabilityAssessmentOutputFactory.Create(sectionResult.Calculation.Output,
+                                                                                                                   failureMechanism, assessmentSection);
+
+            return derivedOutput.Probability;
+        }
+    }
+}
\ No newline at end of file
Index: Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Data/Ringtoets.HeightStructures.Data.csproj
===================================================================
diff -u -r0bd593582cccd21f905e704d238d7359c0005028 -r4c8e08fbec305b763ae716ae7a3660d75c4c7b99
--- Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Data/Ringtoets.HeightStructures.Data.csproj	(.../Ringtoets.HeightStructures.Data.csproj)	(revision 0bd593582cccd21f905e704d238d7359c0005028)
+++ Ringtoets/HeightStructures/src/Ringtoets.HeightStructures.Data/Ringtoets.HeightStructures.Data.csproj	(.../Ringtoets.HeightStructures.Data.csproj)	(revision 4c8e08fbec305b763ae716ae7a3660d75c4c7b99)
@@ -14,6 +14,7 @@
     <Compile Include="GeneralHeightStructuresInput.cs" />
     <Compile Include="HeightStructure.cs" />
     <Compile Include="HeightStructuresFailureMechanism.cs" />
+    <Compile Include="HeightStructuresFailureMechanismSection2aAssessmentResultExtensions.cs" />
     <Compile Include="HeightStructuresFailureMechanismSectionResult.cs" />
     <Compile Include="HeightStructuresInput.cs" />
     <Compile Include="HeightStructuresProbabilityAssessmentOutputFactory.cs" />
Index: Ringtoets/HeightStructures/test/Ringtoets.HeightStructures.Data.Test/HeightStructuresfailureMechanismSection2aAssessmentResultExtensionsTest.cs
===================================================================
diff -u
--- Ringtoets/HeightStructures/test/Ringtoets.HeightStructures.Data.Test/HeightStructuresfailureMechanismSection2aAssessmentResultExtensionsTest.cs	(revision 0)
+++ Ringtoets/HeightStructures/test/Ringtoets.HeightStructures.Data.Test/HeightStructuresfailureMechanismSection2aAssessmentResultExtensionsTest.cs	(revision 4c8e08fbec305b763ae716ae7a3660d75c4c7b99)
@@ -0,0 +1,155 @@
+// Copyright (C) Stichting Deltares 2017. All rights reserved.
+//
+// This file is part of Ringtoets.
+//
+// Ringtoets is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program. If not, see <http://www.gnu.org/licenses/>.
+//
+// All names, logos, and references to "Deltares" are registered trademarks of
+// Stichting Deltares and remain full property of Stichting Deltares at all times.
+// All rights reserved.
+
+using System;
+using NUnit.Framework;
+using Rhino.Mocks;
+using Ringtoets.Common.Data.AssessmentSection;
+using Ringtoets.Common.Data.FailureMechanism;
+using Ringtoets.Common.Data.Structures;
+using Ringtoets.Common.Data.TestUtil;
+using Ringtoets.HeightStructures.Data.TestUtil;
+
+namespace Ringtoets.HeightStructures.Data.Test
+{
+    [TestFixture]
+    public class HeightStructuresFailureMechanismSection2aAssessmentResultExtensionsTest
+    {
+        [Test]
+        public void GetAssessmentLayerTwoA_SectionResultNull_ThrowsArgumentNullException()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var assessmentSection = mocks.Stub<IAssessmentSection>();
+            mocks.ReplayAll();
+
+            // Call
+            TestDelegate call = () => HeightStructuresFailureMechanismSection2aAssessmentResultExtensions.GetAssessmentLayerTwoA(null,
+                                                                                                                                 new HeightStructuresFailureMechanism(),
+                                                                                                                                 assessmentSection);
+
+            // Assert
+            var exception = Assert.Throws<ArgumentNullException>(call);
+            Assert.AreEqual("sectionResult", exception.ParamName);
+            mocks.VerifyAll();
+        }
+
+        [Test]
+        public void GetAssessmentLayerTwoA_FailureMechanismNull_ThrowsArgumentNullException()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var assessmentSection = mocks.Stub<IAssessmentSection>();
+            mocks.ReplayAll();
+
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var failureMechanismSectionResult = new StructuresFailureMechanismSectionResult<HeightStructuresInput>(section);
+
+            // Call
+            TestDelegate call = () => failureMechanismSectionResult.GetAssessmentLayerTwoA(null, assessmentSection);
+
+            // Assert
+            var exception = Assert.Throws<ArgumentNullException>(call);
+            Assert.AreEqual("failureMechanism", exception.ParamName);
+            mocks.VerifyAll();
+        }
+
+        [Test]
+        public void GetAssessmentLayerTwoA_AssessmentSectionNull_ThrowsArgumentNullException()
+        {
+            // Setup
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var failureMechanismSectionResult = new StructuresFailureMechanismSectionResult<HeightStructuresInput>(section);
+
+            // Call
+            TestDelegate call = () => failureMechanismSectionResult.GetAssessmentLayerTwoA(new HeightStructuresFailureMechanism(), null);
+
+            // Assert
+            var exception = Assert.Throws<ArgumentNullException>(call);
+            Assert.AreEqual("assessmentSection", exception.ParamName);
+        }
+
+        [Test]
+        public void GetAssessmentLayerTwoA_SectionResultWithoutCalculation_ReturnsNaN()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var assessmentSection = mocks.Stub<IAssessmentSection>();
+            mocks.ReplayAll();
+
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var failureMechanismSectionResult = new StructuresFailureMechanismSectionResult<HeightStructuresInput>(section);
+
+            // Call
+            double assessmentLayerTwoA = failureMechanismSectionResult.GetAssessmentLayerTwoA(new HeightStructuresFailureMechanism(), assessmentSection);
+
+            // Assert
+            Assert.IsNaN(assessmentLayerTwoA);
+        }
+
+        [Test]
+        public void GetAssessmentLayerTwoA_CalculationWithoutOutput_ReturnsNaN()
+        {
+            // Setup
+            var mocks = new MockRepository();
+            var assessmentSection = mocks.Stub<IAssessmentSection>();
+            mocks.ReplayAll();
+
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var failureMechanismSectionResult = new StructuresFailureMechanismSectionResult<HeightStructuresInput>(section)
+            {
+                Calculation = new TestHeightStructuresCalculation()
+            };
+
+            // Call
+            double assessmentLayerTwoA = failureMechanismSectionResult.GetAssessmentLayerTwoA(new HeightStructuresFailureMechanism(), assessmentSection);
+
+            // Assert
+            Assert.IsNaN(assessmentLayerTwoA);
+        }
+
+        [Test]
+        public void GetAssessmentLayerTwoA_CalculationWithOutput_ReturnsDerivedProbability()
+        {
+            // Setup
+            var failureMechanism = new HeightStructuresFailureMechanism();
+
+            var mocks = new MockRepository();
+            IAssessmentSection assessmentSection = AssessmentSectionHelper.CreateAssessmentSectionStub(failureMechanism, mocks);
+
+            FailureMechanismSection section = FailureMechanismSectionTestFactory.CreateFailureMechanismSection();
+            var failureMechanismSectionResult = new StructuresFailureMechanismSectionResult<HeightStructuresInput>(section)
+            {
+                Calculation = new TestHeightStructuresCalculation
+                {
+                    Output = new TestStructuresOutput()
+                }
+            };
+
+            // Call
+            double assessmentLayerTwoA = failureMechanismSectionResult.GetAssessmentLayerTwoA(new HeightStructuresFailureMechanism(), assessmentSection);
+
+            // Assert
+            Assert.AreEqual(0.5, assessmentLayerTwoA);
+            mocks.VerifyAll();
+        }
+    }
+}
\ No newline at end of file
Index: Ringtoets/HeightStructures/test/Ringtoets.HeightStructures.Data.Test/Ringtoets.HeightStructures.Data.Test.csproj
===================================================================
diff -u -r0bd593582cccd21f905e704d238d7359c0005028 -r4c8e08fbec305b763ae716ae7a3660d75c4c7b99
--- Ringtoets/HeightStructures/test/Ringtoets.HeightStructures.Data.Test/Ringtoets.HeightStructures.Data.Test.csproj	(.../Ringtoets.HeightStructures.Data.Test.csproj)	(revision 0bd593582cccd21f905e704d238d7359c0005028)
+++ Ringtoets/HeightStructures/test/Ringtoets.HeightStructures.Data.Test/Ringtoets.HeightStructures.Data.Test.csproj	(.../Ringtoets.HeightStructures.Data.Test.csproj)	(revision 4c8e08fbec305b763ae716ae7a3660d75c4c7b99)
@@ -20,6 +20,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="GeneralHeightStructuresInputTest.cs" />
+    <Compile Include="HeightStructuresFailureMechanismSection2aAssessmentResultExtensionsTest.cs" />
     <Compile Include="HeightStructuresFailureMechanismSectionResultTest.cs" />
     <Compile Include="HeightStructuresFailureMechanismTest.cs" />
     <Compile Include="HeightStructuresInputTest.cs" />