Freelance Traveller

by Robert O'Connor

Part 2: Taints, Noble Gases, and Nitrogen

Taints

Many worlds in Traveller have tainted atmospheres, which contain oxygen and some other substances that may inconvenience residents and visitors. The following points may be of interest to world builders.

The following broad categories of taints were included in "First In" and the "World Builder's Handbook":

• Halogens (chlorine/fluorine)
• Sulphur and nitrogen compounds
• Hyperoxic and hypoxic atmospheres
• Carbon dioxide
• Inert gases
• Disease/allergens - biological pathogens
• Pollutants

The limits to, and effects of, oxygen concentration were discussed in the previous part of this series. Carbon dioxide is an excellent greenhouse gas and more than 0.2 atm would eventually lead to a Venus style runaway. It will be discussed with other carbon compounds, halogens and sulphur compounds later.

Particulate materials are of interest. The following generalisations can be made:

Only 30% of 0.5 micrometre particles remain in the lung during normal resting breathing (the rest are exhaled).

Clearance of retained particles is via two mechanisms: uptake by tissue macrophages and the 'mucociliary elevator' - an adult human produces about 40-50cc of mucus a day from the respiratory tree; usually this is swallowed.

Inhalation of particulates can have a range of effects, e.g.

• cough, wheeze, shortness of breath, bronchospasm (asthma);
• pneumonia, pneumonitis, fibrosis (scarring) of the lung from chronic irritation and inflammation ; some rare cancers.

[Concentrations are in micrograms/m³ air at 1 atm and 25C]

An alternate taint classification might be:

1. Chemical
   • Inert gases - simple asphyxiants (reduce oxygen levels ; recall the effects of hypoxia!) e.g. 'noble gases', nitrogen
   • Irritant gases - cause injury to respiratory tract e.g. ozone
   • Chemical asphyxiants - inhibit cellular respiration e.g. carbon monoxide
2. Particulates
   • Non-biological :- volcanic, metal (and metal salt) dusts, asbestos and other silicates
   • Biological :- pollens, spores, virions, decomposing or 'waste' matter  e.g. bagasse from sugar cane processing, hay
3. Radiation
   • high background count : cosmic/gamma/UV also falls into particulates category (e.g. post nuclear weapons detonation)

The 'Noble' Gases

So named because of their lack of reactivity, these elements may be present in large amounts in planetary atmospheres.

Data

[melting and boiling points at 1 atm, in degrees celsius]

1. Helium

   The second most abundant element in the universe, helium is usually found in significant amounts only in the atmospheres of subgiant or gas giant worlds due to its low molecular weight (helium makes up 0.00052% of Earth's atmosphere).

   It may be found dissolved in hydrocarbons or similar non-polar solvents on less massive worlds. The primary supply of helium on Earth is that dissolved in the gas and oil fields of the American Mid-West.

   Helium's main uses are in cryogenics, as a lifting gas for balloons and airships, and in medicine and diving as a poorly soluble gas that has better flow characteristics than nitrogen or oxygen, reducing airway resistance and hence the work of breathing.

   It is also used in lung function testing and in circulatory assist devices (the intra-aortic balloon pump).

2. Neon and Krypton

   Neon is the fifth most abundant element in the universe. Neon and krypton are used primarily to generate red and orange light respectively in the presence of electrical current (signage and lasers).

3. Argon and Xenon

   Argon is 15th in the 'top thirty'. Argon is used in diving to prevent oxygen or other gas toxicity with deep dives ; it is a general anaesthetic in amounts in excess of 7 atmospheres pressure, and will cause intoxication above 5 atmospheres pressure.

   Like some of the other elements in this group, argon is used in lamps and lasers.

   Xenon is out of the 'top thirty' but is included for completeness. Xenon will cause general anaesthesia in amounts of 0.7 atm or greater (with intoxication above 0.6 atm), and has been used clinically for the former purpose.

   Xenon, argon and krypton will form compounds with fluorine under certain extreme conditions. Xenon hexafluoroplatinate (XePtF₆) is an example of one of the more stable compounds.

   Neon, krypton, argon and xenon are distilled from the atmosphere. They are present in trace amounts in the atmospheres of Earthlike worlds.

4. Radon

   Is produced by the decay of radium 226, and contributes in a small way to background radiation (the estimated average contribution by radon in the continental US is 2-3 picocuries per litre of air - about one one-millionth the amount produced by a smoke detector).

   Minerals on Earthlike worlds typically have heavy nuclide contents on the order of one part in 1-10 million ; high metal content worlds could have much more.

   So radon levels are determined by the radium content of soils, rocks, building materials formed from these and ground water. There is currently some controversy about radon levels and carcinogenesis in the epidemiology literature.

Nitrogen

Data: Formula N₂, molecular weight 28, melts at -210C, boils at -196C, critical temperature -147C, 'inert gas'.

Compounds of nitrogen are relatively difficult to form. Much of the nitrogen found on Earthlike worlds is in the atmosphere or in the upper layers of the crust.

On iceball worlds, nitrogen may become an prominent element of the local geology e.g. the geysers of Neptune's moon, Triton. Nitrogen has some applications in cryogenics. Compounds of nitrogen are important as they are incorporated into amino acids and nucleotides, apart from their myriad industrial applications.

N₂ will cause 'nitrogen narcosis' or 'rapture of the deep' with levels in excess of 3-4 atm pressure. The initial symptoms are similar to low level ethanol intoxication, with the eventual onset of general anaesthesia with levels of 10 atm or more.

Some compounds that may be present as atmospheric taints include

1. Nitrous oxide (N₂O)

   Data : mp -91C, bp -88C, 'inert gas'

   Produced industrially by heating ammonium nitrate under pressure, nitrous is relatively reactive, forming higher oxides of nitrogen. Therefore ongoing synthesis is required, be it by biological or geological processes.

   Acutely, N₂O has a calmative effect at levels of 0.25-0.5 atm, similar to moderate ethanol intake. Above 0.6 atm, it has good pain relieving properties. General anaesthesia occurs in 50% of subjects at levels of 1.12 atm. Chronic exposure leads to anaemia via inhibition of synthesis of the amino acid methionine. Inhibition of the activity of vitamin B₁₂ can cause degeneration of the spinal cord, leading to spasticity and paralysis which is irreversible without nerve regeneration technology.

2. Nitric oxide (NO)

   Data: mp -164C, bp -152C.

   Could be grouped in both 'irritant' and 'chemical asphyxiant' classes. This compound is a very reactive species and mediates vasodilatation and neurotransmission in most Earthly life. Like N₂O, some process must exist to maintain its ambient levels if it is to be a sustained taint.

   Primary toxicity is via binding to sulphur and iron atoms, causing derangements to protein function, especially in the cells of the lung and heart. Oxygen transport is impaired via the oxidation of iron in haemoglobin (needs to be Fe²⁺ -> changed to Fe³⁺, which can't bind oxygen).

   It is used therapeutically in some refractory cases of pulmonary hypertension and other lung disorders. The dosage ranges from 0.06 to 80 parts per million inhaled [1 atm pressure, 25C].

   Reversible lung injury is likely with sustained exposure (>8 hours) in excess of 25ppm.

3. Other oxides of nitrogen

   NO₂, N₂O₃, N₂O₄

   All of these compounds are gases or have significant vapour pressures over -50C. They are all powerful lung irritants, causing inflammation, and bronchospasm. Death is typically due to ventilatory failure.

   'Silo-filler's disease' was a syndrome of cough, bronchospasm and eventual collapse noted in the early days of grain silo use.

   Stored grains release some of their nitrogen content as nitrogen oxides. There were a number of anaesthetic related deaths and injuries following the use of a nitrous oxide supply that had been contaminated with these compounds in a British hospital in the 1960s.

   Concentration	Effect
   6-10	statutory limits for occupational exposure (8 hours/24)
   50-150	airway inflammation - cough, shortness of breath in all persons exposed
   350	50% of subjects exposed will die*
   560-940	lethal dose to 100% of subjects exposed*

   [concentration measured in mg/m³ air at 1 atm and 25C; * - estimated!]

   Other sources of higher oxides of nitrogen include combustion and volcanic activity.

4. Ammonia (NH₃)

   Data mp -78C, bp -33C, critical temperature 127C.

   One of the most common compounds in the universe.

   An irritant gas at the appropriate temperature ranges.

   Concentration	Effect
   25-50	Odor threshold. Occupational exposure limit 50 ppm
   100	Eye irritation
   500	immediate danger to life/health
   1000	caustic effects on respiratory tract
   2500	death within 30 mins possible
   30000	death within 5 minutes possible

   [Concentrations are in parts per million at 1 atm and 25C]

5. Hydrazine (N₂H₄)

   Data mp 1C, bp 114C.

   Hydrazine is a rocket fuel, most commonly used in satellites' "stationkeeping" propulsion systems. It is also used as a cleaning agent and in the synthesis of rubber and some pharmaceuticals and agricultural chemicals.

   Hydrazine's flash point (the minimum temperature of a liquid or solid at which it gives off enough vapour to form an ignitable mixture with air) is 38C (it burns with a violet flame).

   It causes marked lung, skin bone marrow and liver toxicity with exposure, and is also a potent carcinogen in animals and probably in man. The occupational exposure limit to hydrazine is 0.03ppm in air over a 2hour period, or 0.1ppm via skin contact over an 8 hour period.

  [ Back | Next ]