Section 7 Design guidance for nuclear, biological and chemical defence

7.1.1 The arrangements of hull structure for chemical, biological, radiological and nuclear defence (CBRN) are to generally be in accordance with the requirements of this section. The final design and arrangements are to be in accordance with a specified standard. Where specifically requested, LR can undertake the inspection and certification of CBRN arrangements or gastight integrity, see Vol 1, Pt 6, Ch 6, 7.6 Gastight testing.

7.1.2 The subdivision of the ship for CBRN defence is achieved by the provision of zones which minimise the consequences of an attack. The zone boundaries provide protective barriers to resist the spread of primary and secondary weapon effects.

7.1.3 The number and location of zone boundaries and distribution of systems within those zones is best determined by carrying out a vulnerability analysis as detailed in Vol 1, Pt 4, Ch 1, 2 Survivability.

7.1.4 The effect of zones on, and requirements for damage control should also be considered. This is best assessed by testing the zone arrangement with a series of ‘what if’ damage scenarios. A good zone arrangement will aid damage control.

7.1.5 An effective CBRN defence is to comprise of three distinct phases:

• Monitoring and detection by the provision of systems to detect the presence of and to identify the threat both outside the ship and within the zones.
• Protection of the ship and crew, using a pressurised citadel and zones with gas-tight boundaries and airlocks. Protection is also achieved with the filtration of air drawn into the ship and enclosing machinery intakes and exhausts.
• Decontamination of spaces within the ship is achieved using a suitable ventilation and filtration system. Decontamination of the ship itself is largely achieved using pre-wetting systems. For the crew and equipment, cleansing stations can be used.

7.2.1 A citadel is the gastight envelope of the hull and superstructure. It consists of a group of interconnecting compartments enclosed by a gas-tight boundary with the independent systems necessary to provide a toxic free area free from any CBRN hazard. Large ships may have subcitadels or more than one citadel.

7.2.2 A zone is a smaller group of compartments within the citadel with some or all of the independent systems necessary to provide a toxic free area that is free from any CBRN hazard.

7.2.3 An airlock is a compartment with two doors between the toxic free area and the source of the CBRN hazard or cleansing station. Airlocks are normally purged with clean air to allow personnel to pass from one area to another without contaminants entering the toxic free area.

7.2.4 A cleansing station is a group of compartments suitably arranged and equipped whereby CBRN decontamination of personnel and materials can take place.

7.2.5 Individual protective equipment is the personal clothing and equipment required to protect an individual from CBRN hazard. It normally consists of a protective suit and respirator.

7.3.1 The requirements of this Section deal only with the hull structure and mainly involve the arrangement of major divisions within the hull. Provision is to be made within the layout and design of the ship for the compartments required for CBRN defence. It is recommended that they are considered from a very early stage in the design.

7.3.2 Unless specified otherwise, the citadel’s length is to be divided into zones. It is recommended that the zone boundaries coincide with main transverse watertight bulkheads and extend from the keel to the highest superstructure deck.

7.3.3 A suitable pressure above atmospheric is to be maintained inside the citadel and zones. Zones with a higher risk of contamination are to be maintained at a lower pressure than the adjacent zones but higher than atmospheric. For example those containing machinery spaces with ventilation to atmosphere open during CBRN conditions.

7.3.4 For NS1 ships at least three cleansing stations are to be provided in separate zones. For NS2 ships at least two cleansing stations are to be provided in separate zones. They are to be located so that safe and direct entry is possible from the weather deck. One cleansing station is to be located close to the medical complex with access for stretcher borne casualties.

7.4.1 The requirements of this Section deal only with the hull structure and mainly involve the arrangement of major divisions within the hull. It is recommended that they are considered from a very early stage in the design.

7.4.2 For NS3 ships it may be impractical to provide zones and a citadel. In this case CBRN protection is to be provided by either individual protective equipment or sanctuaries.

7.4.3 Sanctuaries may be integral or temporary compartments on board the ship and are to be provided with an airlock, cleansing station and ventilation systems similar to that of a zone.

7.4.4 If individual protective equipment is provided arrangements are to be made to ensure that operation of the ship is possible such that it can reach a suitable place of refuge. For example, crew provisions, equipment and compartment accesses are to be suitable for persons wearing individual protective equipment.

7.5.1 The boundaries of zones are to be gastight and are to be tested in accordance with Vol 1, Pt 6, Ch 6, 7.6 Gastight testing. Ventilation and trunking is not to pass through zone boundaries.

7.5.2 Each zone is generally to be provided with a total air conditioning system. All air entering the citadel is to pass through CBRN filters. These filters may be bypassed when the ship is not in a threat situation.

7.5.3 Consideration is to be given to the provision of independent services in each zone for the following systems:

1. Electrical power generation and distribution.

2. Chilled water cooling.

3. Fire pumps, piping and hydrants (including pre-wetting).

4. Bilge pumps, piping and discharge.

5. Internal communications.

6. Machinery or damage control surveillance or control.

7. Compressed air.

8. Emergency crew support.

9. Smoke clearance arrangements.

10. Air start arrangements in the appropriate zones.

7.5.4 At least two airlocks to the weather decks are to be provided in each zone. Access between zones are to be fitted with airlocks. Consideration is to be given to providing gas-tight connections adjacent to this access for the provision of the services listed in Vol 1, Pt 4, Ch 1, 7.5 Zones 7.5.3.

7.5.5 Consideration should be given to the use of materials that do not emit toxic fumes.

7.6.1 In determining the layout and design of the ship consideration should be given to the hardening of the ship to improve its capability in an CBRN environment.

7.6.2 All external compartments and equipment not included in the citadel should be sealed or designed such that residual contaminants cannot be trapped.

7.6.3 All access for operation and maintenance of equipment should be designed for personnel wearing individual protective equipment.

7.6.4 Shelters are to be provided deep within the ship for the temporary protection from radiation of the crew during nuclear attack.

7.6.5 Command and control centres should ideally be sited such that they are afforded the maximum protection against radiation from nuclear attack. All relevant Mobility and Ship Type equipment should be designed to resist incident nuclear radiation (INR) and nuclear electromagnetic pulse (NEMP).

7.7.1 The scantlings of all gas-tight zone, citadel and airlock boundaries are to be capable of withstanding two times the maximum differential pressure that can occur in service and the scantlings are to be calculated in accordance with the relevant Sections of Vol 1, Pt 6, Ch 3 Scantling Determination. Gas-tight boundaries are to be tested in accordance with Vol 1, Pt 6, Ch 6, 7.6 Gastight testing.

7.7.2 All openings in gastight boundaries are to be fitted with gas-tight closing appliances and tested in accordance with Vol 1, Pt 6, Ch 6, 7.6 Gastight testing and are to be of equivalent strength to the structure in which they are placed.

7.7.3 Watertight and weathertight closing appliances may be considered gas-tight if a pressure greater than atmospheric is, and can be maintained inside the zone, citadel or airlock.