(Originally submitted to the GURPS Traveller: Starships playtest newsgroup.)

Most spacecraft fuels are dangerous substances. Nearly all are inflammable; some form explosive mixtures with air; some are cooled to near absolute zero. With proper handling these substances are no more dangerous than the gasoline in your automobile. However, handled improperly, they can become extremely hazardous to the health of a starship.

The regulation fuel tanks in Traveller spacecraft are self-sealing, pressurized and are protected internally by DR50 bulkheads and a double wall filled with inert gas. Starships will generally have their fuel tankage divided into no more than four tanks of equal size; those with heavy compartmentalisation have no more than eight; and those with total compartmentalisation, sixteen. For each tank cross-reference its size on the Hull Table on GT151 to get the surface area; this figure is also its number of hit points.

Whenever a fuel tank takes 10% or more of its hit points from a single attack, roll three dice and compare to the tank's Fire Number (see table below); if the roll is equal or less then the tank catches fire. There must be oxygen present for LHyd, jet fuel and metal fuel to burn. Liquid oxygen itself does not burn, but most substances when exposed to a high concentration of oxygen will.

DMs: Attacked by flame, laser, plasma, or fusion weapon, +4; LOX tank in air or vacuum -5; not self-sealing +1; not pressurized +2*; not double-walled +2*; TL7 +2. *Not applicable to Collapsible tanks. (Note: these numbers are fully equivalent to the Fire Numbers given in VE89-90, but in a form more convenient for the GURPS Traveller player.)

Explosion

Once a tank catches fire, roll 3d vs half the Fire Number every second. Success means that the tank explodes. If the fire has occurred internally and the ship is still pressurised, the ship takes damage equal to 6d x 30 x Ns, where Ns is the number of contiguous empty spaces adjacent to the tank. To find Ns, determine which bulkhead doors are open or bulkheads breached; on each connected deck and compartment between bulkheads, add the full number of spaces for each stateroom, bunk room, office or other inhabited module; add half the spaces for any functional module such as jump drives, bridge, low berth, etc; and add from 100% to 5% of the cargo hold, depending on how full it is.

For example, if one of the saddle fuel tanks on the Beowulf illustrated on GT133 exploded, the cargo bay was empty and all bulkhead doors were sealed, then Ns = 34.5 (lower cargo bay plus air/raft bay), meaning that an explosion of 6d x 1035 would occur. If all bulkhead doors were open but between-decks sealed, then Ns = 67, giving an explosive yield of 6d x 2010.

If a detailed deck-plan is not available, assume that the bridge, jump drive room, maneuver drive room, power-plant room, cargo bay, vehicle bays and recreation facilities are each undivided air-tight compartments. The remainder of the vessel will be sub-divided into no more than four compartments per 1000 dtons of remainder normally, eight if heavily compartmentalised, and sixteen if total. The power plant room may be subdivided into the same number of compartments as Engineering Modules fitted.

Calculate the damage to the sealed bulkheads, decks and external armour where necessary (remembering that DR is squared against explosion). If a bulkhead or deck is breached, then the next set of contiguous spaces will also explode. And so on, until the fuel is used up (assume 10 lbs per space). If the total of explosive damage exceeds the hit points of the ship then it is disabled, as per GT168, and if the total exceeds five times the ship's hit points it is destroyed.

Effects of Fire

A vessel on fire suffers 2d damage, plus another 2d every 10 seconds, in the compartment where the fire is taking place, DMs -2 for heavy compartmentalisation, -4 for total. The fire may be extinguished by fire suppression systems, manually by the crew, or by depressurising the compartment. Every ten seconds, each fire that did 8 or more damage may spawn another fire. However, if an individual fire did less than 4 hits damage, that fire dies.

Fire Suppression

Fortunately, all Traveller spacecraft have fire and explosion suppression systems. Such systems comprise: pressure, temperature, particle (smoke), and chemical sensors distributed liberally around the vessel; tanks of chemical extinguishers, combustion inhibitors and thermal barrier substances; high-speed valves and power cut-offs to equipment; and a control system, independent of the main computer and power systems, capable of analysing a hazard and reacting appropriately within roughly 1/30th of a second.

Roll TL-2 each second, /before/ rolling for explosion; DM -1 for each separate fire, +4 per Engineering Module installed after the first. A successful roll means the fire is out. If the GM rules that the fire suppression system is inoperative then crew may attempt to put out the fire manually. Once every ten seconds roll 6 or less, or TL+2 or less if using hand-held extinguishers, per person per fire to put out the fire. A roll of 17 or 18 means that the fire-fighter has taken 2d burn damage.

Leaks

If a fire is put out, the fuel tank will still be leaking. A hydrogen fuel tank loses a gallon of fuel for every 1 point of damage inflicted (other tanks lose 1 gallon per 10 points) and unless self-sealing, leaks the same amount each minute. If a self-sealing tank has taken less than 100 points of damage at TL7, 200 at TL8 or 400 at TL9+, then it will reseal in one minute. If the tank takes more damage than this, then after one minute recompute the leak as above taking this figure from the damage. For example, a TL9 self-sealing hydrogen tank takes 80 points damage; in the first minute it will leak 80 gallons, in subsequent minutes it will leak 40 gallons per minute.

These leaks will still constitute a fire hazard in the presence of oxygen. Jet fuel and metal fuel will spread out and catch fire if ignited by sparks, energy weapons or flame. Cryogenic fuels such as LHyd will evaporate almost instantaneously. LHyd itself may then form an explosive mixture with air, which again may be set off by flame, spark or energy weapon. Work out Ns as above; if Ns is less than 16 times the number of gallons that has leaked then there is a risk of explosion of 6d x 6 damage per gallon, up to the limit of 6d x 30 x Ns.

Vacuum

Contrary to popular belief, it is the risk of fire and explosion if fuel tanks are damaged that leads to some Naval vessels depressurising prior to combat. On large ships, this may mean just those compartments adjacent to fuel tanks, while smaller vessels may depressurise entirely except for the bridge, life-support and engineering. This has been mandated at various times during the Imperial Navy's history; the awkwardness of attempting to operate controls while vacc-suited has resulted in the current doctrine of leaving it to the discretion of the individual commander.

Perversely, it is this fire risk that causes some commanders to re-pressurise in the event of an attempted boarding, in order to limit the force that can be applied by the boarding parties. An FGMP-12, for example, will quite adequately blow-through several bulkheads if mis-aimed, leaving open the possibility of causing an explosion if a fuel tank is breached and destroying whatever the boarding party is in search of.

A compartment may be depressurised manually, from the bridge or engineering, and on naval ships from within the compartment itself, using lifesystem ventilation. This takes 5 x (15-TL) seconds to reach a level insufficient to support combustion and respiration. If a compartment is adjacent to vacuum, it may be depressurised by opening airlocks or cargo doors, taking 5 seconds to depressurise. This will put out an existing fire, but may leave hot spots that will reignite on a 12+ on 3d when pressure is restored. These may be sprayed with fire suppressant prior to repressurisation, but inspecting for hotspots takes 20 minutes per compartment per person, counting each person with infra-red vision aids as four.

If LHyd is leaking into a depressurised compartment at normal temperature, then it will quickly boil off as above, but will not form a fire hazard unless the compartment or ship is sealed and the hydrogen is exposed to oxygen, say from a damaged vacc-suit air-tank. If an airtank is damaged, roll against the fire number (do /not/ use the DM for LOX in air), and roll for explosion, as above, taking each pound of air to be equivalent to 4d damage and each pound of pure oxygen equivalent to 6d x 3. If the ship's fire suppression system is active, then rolls for fire suppression can be made.

A vacc-suit will protect against hydrogen gas exposure for brief periods. However, the hydrogen gas molecule is very small and will find gaps too tiny to allow larger molecules through. Its presence may then cause bizarre and not-easily predictable effects on life-support filters, vacuum lubricants, readouts, etc. Vacc-suits will therefore need 1d hours maintenance after exposure to hydrogen gas atmospheres, and will need to roll 6+ on 3d every ten minutes to avoid malfunction while exposed (GMs note: these can be anything from an annoyingly bad smell to a truly evil stench, false alarms, failed alarms, unreadable readouts, random comm channel switching, stuck valves, etc; be creative). Any carried equipment or weapons may also be subject to these effects, unless certified proof against hydrogen atmosphere.

Boiling Floods of Liquid Hydrogen!

A fuel tank that receives its hit points in damage will rupture, spilling its contents. Barring an explosion the LHyd will advance at Move 30 into an open space, Move 100 along a sealed corridor. Personnel must roll their ST on 3d to keep their footing in the flood, DM -4 if running.

Personnel exposed to this extreme cold must roll HT-16 every second, or lose 1d points of Fatigue. When ST reaches 3, start losing HT instead. Modifiers: as B130, Freezing, plus; vacc-suit +10; combat armour +11; battledress +13; improved battledress +14.

Individuals who lose HT due to cold will suffer frostbite: apply 1 pt of the damage to each extremity, starting with hands, then feet, then arms, legs, and head. Apply 2 pts if the body part is exposed or in contact with a cold, non-insulating surface. Placing the victim in above-freezing temperatures and making a successful roll against First-aid, Physician or Survival (Arctic) will restore 1 pt to each limb.

All equipment exposed to contact with LHyd should roll against HT; failure means the equipment has broken. Critical failure on life-support equipment indicates that an air tank has fractured; roll against item HT to avoid an explosion.

Personnel can breath air contaminated with hydrogen gas without ill effect, though their voices will become higher pitched, possibly to the point of incomprehensibility. Such air is very cold; assume an air temperature of -200 F, and use the Freezing rules on B130, DMs as above.

This page updated Tuesday, May 30, 2006 around about 18:30 ish (BST)