Neutral Buoyancy Research Facility
Diving Safety Manual

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Section 7
Design Requirements for
Test Hardware

last modified 001020

7.1 Overall Philosophy

This section describes desirable and proscribed hardware design features that impact safety. It is not appropriate in this document to list all of the lessoned learned in the Space Systems Laboratory over the last 25 years on how to design neutral buoyancy hardware, but there are design decisions that can be made to enhance (or decrease) system safety.

7.2 Standard Hardware Requirements

Underwater hardware shall be designed and manufactured to fulfill its test function(s) while not negatively affecting safety for the divers or the operations of the facility.

7.2.1 Materials Selection

Materials used in the Neutral Buoyancy Research Facility shall be compatible with long-term exposure to chlorinated water at 90°F.

Metals - Recommended metals are aluminum (with anodized or painted surfaces to resist corrosion) or stainless steel.

Plastics - Most plastics are acceptable, although the design implementation should take into account the tendency of many plastics to absorb water with time.

Flotation - Foam is commonly used for flotation, and should be closed-cell rigid foam capable of taking the 12 pounds/square inch pressure at the bottom of the NBRF with minimal change in volume. Hydrophilic foams should be coated with penetrating epoxy to prevent water absorbtion. Sealed PVC tubes are useful for large amounts of flotation, but should be at least Schedule 40 PVC to resist water pressure. Mounting systems for flotation shall be capable of supporting the full flotation force with a factor of safety of at least 2.

7.2.2 Design Safety Details

Physical design details which affect safety are primarily based on abrasion, trauma, pinching, and entrapment.

• Sharp edges and corners are not acceptable. All edges and corners shall be rounded to a minimum radius of 0.06 inches.
• Surface finish should be smooth enough to avoid abrasion to sensitive skin tissues. It is recommended that a minimum surface finish of <TBD> should be maintained.
• Exposed thin metal sheets must either have rolled edges, or edge covering to a minimum radius of 0.06 inches.
• Articulated hardware shall be designed to eliminate pinch points. Where elimination is not practical, critical pinch areas shall be identified, and usage techniques developed to prevent pinching and briefed to the underwater personnel prior to flight.
• Hardware shall be designed to prevent entrapment of air, which could create significant changes in buoyancy. Vent holes or porous materials shall be provided to prevent air from pooling inside underwater hardware.
• Hardware shall be designed and operated to eliminate the danger of entraping underwater personnel. Hardware mounting systems shall prevent toppling under credible loading conditions. Restricted volumes shall be designed to preclude inadvertant entry of dive personnel.
• Lift points for the NBRF overhead hoist systems shall be designed, fabricated, and mounted to support the full weight of the hardware with a factor of safety of at least 2. Lift points for lift bag attachment shall be capable of holding full weight of the hardware, and shall be selected and briefed to divers prior to test operations.

7.3 Electrical Hardware Requirements

Primary safety implications of electrical power use underwater deals with shock and electrocution hazards to dive personnel, and to support personnel on the surface in a wet and humid environment.

• All electrical equipment within 10 feet of the water shall be plugged into a receptacle with a ground-fault interrupt (GFI). All GFI hardware shall be checked on a monthly basis.
• All electrical wires which touch the water are limited to a maximum of 32 volts DC.
• All on-board power shall be supplied by batteries which do not vent flammable gases in a nominal discharge situation.
• On-board batteries with a cumulative energy capacity above 100 W-hrs must be physically isolated (separately hermetically sealed) from any ignition sources, including motors, switches, and major circuit boards.
• On-board batteries with a cumulative energy capacity above 2000 W-hrs must be in a sealed battery compartment which is purged with nitrogen (or equivalent nonflammable gas) prior to and following test operations, and which maintains constant internal pressure regardless of water depth.
• Under no circumstances will battery charging take place within a sealed or constrained volume. During charging operations, batteries will be removed from the vehicle, in an substantially open section of the vehicle, or continuously purged with a nonflammable gas.

7.4 Test Readiness Review

Before the first time in the water, test hardware which is either new or substantially modified shall undergo a test readiness review. Prior to the first time in the water, the hardware shall undergo a Test Readiness Review performed by a three-person team. This team shall be comprised of the Facilities Director, Diving Operations Manager, and/or lead divers as designated by the Facilities Director. The Safety Review Team will inspect the hardware for adherence to the NBRF Diving Safety Manual, with specific attention to the hardware requirements in this Section. The review team will also consider the planned test operations, including requirements of dive skills of test crew and other issues affecting test safety. The individual(s) responsible for the test shall participate in the Test Readiness Review, and should be prepared to answer questions and provide requested information, including test procedures, circuit schematics, and deck testing results.

7.5 Dive Readiness Review

Before each dive, test hardware shall be inspected by the Deck Chief and the Lead Diver prior to installation in the NBRF. If there are any questions on the safety or servicability of the hardware, the NBRF Facility Director shall be called in to review the hardware, and to provide a decision to allow or forbid use, or to mandate modifications prior to use.