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Hydrogen fluoride

DESIGNATIONS

CAS No.: 7664-39-3
Registry name: Hydrogen fluoride
Chemical name: Hydrogen fluoride
Synonyms, Trade names: Hydrogen fluoride (anhydrous), anhydrous hydrofluoric acid, AHF
as aqueous solutions: hydrofluoric acid, acidum hydrofluorium
Chemical name (German): Fluorwasserstoff (wasserfrei), Flusure (wasserfrei)
Chemical names (French): Fluorure d'hydrogne (anhydre), acide hydrofluorique (anhydre)
Appearance: colourless, highly mobile, caustic liquid with penetrating odour

BASIC CHEMICAL AND PHYSICAL DATA

Empirical formula: HF (mostly as (HF)6 to (HF)x)
Rel. molecular mass: 20.01 g
Density: 1.015 g/cm3 at 0C, 0.901 g/cm3 at boiling point
Relative gas density: 1.77
Boiling point: 19.51C
Melting point: -83.55C
Vapour pressure: 105 Pa at 20C, 1.5 x 105 Pa at 30C, 2.8 x 105 Pa at 50C
Odour threshold: 0.03 mg/m3
Solvolysis/solubility: - HF is extremely hygroscopic and miscible in any ratio with water and numerous organic substances (e.g. with alcohols, ethers, ketones and nitriles).
- Scarcely miscible with hydrocarbons and their halogen derivates
Conversion factors: 1 ppm = 0.832 mg/m3
1 mg/m3 = 1.20 ppm

ORIGIN AND USE

Usage:
Anhydrous hydrogen fluoride is used mainly to produce aerosol fluorocarbons (propellants, refrigerators) as well as metal fluorides, ammonia hydrogen fluoride and fluorosulphuric acid. It is likewise used to desulphurise gas oils and as a solvent in chemical laboratories.

Origin/derivation:
HF issues from rock magma and is thus encountered above all in volcanically active areas (e.g. approx. 200,000 t/a in the 'Valley of the 10,000 Vapours' covering 72 km2 in Alaska).

The industrial production of HF involves the heating of fluorides with concentrated sulphuric acid or thermal decomposition of fluorosilicic acid with the formation of silicon tetrafluoride.

Production figures:
In the "Western" world: 1964 approx. 555,000 t; 1970 approx. 960,000 t; 1972 approx. 1,045,000 t; 1980 approx. 1,820,000 t (ULLMANN, 1985), 1982 approx. 860,000 t (ULLMANN, 1988)

Emissions:
In addition to natural sources, emissions are to be expected from all industries using HF such as aluminium foundries and glassworks, brickworks, enamelling companies and phosphate factories.

Toxicity

Humans: LD50 ppm, inhalation (30-60 min) acc. HOMMEL, 1987
Mammals:
Rat LD50 1276 ppm, inhalation (1 h) acc. ROTH, 1988
Aquatic organisms:
Fish LC 60 mg/l acc. HOMMEL, 1987
Fish LC0 0.63 g/l acc. HOMMEL, 1987
Bacteria 0.63 g/l (inhibited cell reproduction) acc. HOMMEL, 1987
Plants:
Crocus 2 g/m3 (276 h, extremely severe leaf necroses) acc. VDI, 1987
Spruce 5.4 g/m3 (270 h, severe necroses) acc. VDI, 1987
Maize 4.7 g/m3 (7 d, 7% leaf chloroses) acc. VDI, 1987
Narcissus 2 g/m3 (276 h, slight to moderate leaf necroses) acc. VDI, 1987
Chrysanthemum 25 g/m3 (114 h, very slight chloroses) acc. VDI, 1987

Classification of plant species according to their relative fluoride sensitivity (from VDI, 1987):

Highly sensitive

American larch Douglas fir Mahonia St. John's wort
Apricot Fan maple Mountain ash Spruce
Ash maple Gladiolus Mountain pine Tulip
Bilberry Lilac Onion Vine
Common pine Hornbeam Peach Weymouth pine
Coral tree Iris Plum Yellow pine
Cranberry Japanese larch Silver fir  
Crocus family Lily-of-the-valley Sorghum  

Sensitive

Acer platanoides Common pine Lucerne Spinach
Alpine knotgrass Copperbeech Maize family Spruce
Amaranth Cranesbill family Mangel wurzel Stellaria media
Ambrosia Cultivated strawberries Melilotus Sumach
Apple Cultivated carnation Mountain ash Sunflower
Apricot Dahlia family Narcissus family Sweet cherry
Arborvitae family Dock Prunis padus Sweet potato
Aspen poplar Douglas fir Peony family Tea-rose
Aster family Dwarf mountain pine Peach Tomato
Beech family European larch Rye Vines
Begonia family Field maple Raspberry Violet
Black pine Giant sequoia Red mulberry Walnut
Black poplar Golden rod family Rhododendron family Wild sorghum
Black walnut Green ash Rhubarb Willow family
Canadian amelanchier Hybrid poplar Seed oats Winter linden
Chenopodium album Incarnate clover Seed wheat  
Cherry plum Japanese yew Silver maple  
Colorado fir Lilac Sorghum  

Less sensitive

Ailanthus glandulosa Canadian amelanchier Dwarf medlar Prunis padus
Amaranth Carrot Elaeagnus Raspberry
American linden Celery False cypress Robinia
American plane Cherry plum Forsythia Siberian elm
Arborvitae Chinese elm Flowering cherry Snowberry
Aubergine Chinese juniper Hemlock spruce Soja bean
Asparagus family Chrysanthemum family Lucerne Sugar cane
Berberis Coffee tree Mountain ash Sumach
Balsam poplar Columbine family Oak family Tobacco
Black alder Cornaceae Pea Tomato
Black elder Cotton Pear Wheat family
Black nightshade Cucumber Petunia White beech
Blackcurrent Cultivated antirrhinum Philadelphus coronarius Wild vine
Buckthorn Cultivated bean Plane Willow family
Burdock family Cultivated pumpkin Plantain family Yarrow
Cabbage Cultivated strawberry Potato Yew
Camellia Dock family Privet family  

Characteristic effects:

Humans/mammals: HF is caustic and can severely damage the respiratory tract with pulmonary oedemas. Symptoms of acute poisoning are burning of the eyes, the skin, the nasal mucous membranes and the mucous membranes in the throat. Long-term inhalation of HF can cause fluorosis (= osteosclerosis) even at small concentrations. Grazing cattle have been found to produce less milk, to grow less, to suffer paralysis and to have damaged teeth following poisoning. Fluorosis is also possible with cattle. Damage to health can occur as soon as the odour becomes perceptible. Fluorine is found as a trace element in bones and teeth. A lack of fluorine may damage human teeth (e.g. caries).

Plants: HF is the most phytotoxic gas. However, the compatibility of plants to HF varies significantly among the various species depending e.g. on the age of the leaves and the stage of development. HF influences the enzyme activity and causes necroses. Damage due to HF is similar to arid damage.

ENVIRONMENTAL BEHAVIOUR

Water:
HF dissolves completely in water with considerable amounts of heat being liberated. Corrosive and toxic mixtures may form over the surface of water. Extremely acidic with little dissociation in aqueous solutions.

Air:
HF develops smoky clouds in humic air. Corrosive mists are formed and remain at ground level because of the relative gas density.

Soil:
Depending on the type of soil, fluorine is found in the form of fluorides as a natural element in concentrations between 10 and 150 ppm. HF causes only little acidification of the soil as it is readily bonded through the effect of lime. Damage to plants as a result of uptake from the soil is only a minor problem.

Conversion, degradation, decomposition products, half-life:
Fluorides may be produced. Most metal fluorides are soluble in water; PbF2, CuF2 and certain alkaline-earth fluorides are hardly soluble in water or not at all.

ENVIRONMENTAL STANDARDS

Medium/ acceptor Sector Country/ organ.

Status

Value Cat. Remarks Source
Water: Emiss. D

L

5 mg/m3   mass flow > 50 g/h12) acc. TA Luft, 1986
  D

G

1 WGK   acc. HOMMEL, 1987
Air:   D

L

1 g/m3 IW1 11) acc. TA Luft, 1986
  D

L

3 g/m3 IW2 11) acc. TA Luft, 1986
  CDN

(L)

1.5 g/m3   24 h, Manitoba acc. UBA, 1981
  CDN

(L)

4.5 g/m3   24 h, Newfoundland acc. UBA, 1981
  CDN

(L)

26 g/m3   24 h, Ontario1) acc. UBA, 1981
  CDN

(L)

7 g/m3   24 h, Ontario2) acc. UBA, 1981
  CDN

(L)

3 g/m3   24 h, Saskatch. acc. UBA, 1981
  DDR

(L)

5 g/m3   24 h acc. DORNIER, 1984
  DDR

(L)

20 g/m3   30 min acc. DORNIER, 1984
  E

(L)

10 g/m3   24 h acc. DORNIER, 1984
  E

(L)

30 g/m3   30 min acc. DORNIER, 1984
  H

(L)

20 g/m3   24 h3) acc. DORNIER, 1984
  H

(L)

1.3 g/m3   24 h4) acc. DORNIER, 1984
  H

(L)

5 g/m3   30 min4) acc. DORNIER, 1984
  NL

(L)

10 g/m3   24 h acc. DORNIER, 1984
  RO

(L)

5 g/m3   24 h acc. DORNIER, 1984
  RO

(L)

20 g/m3   30 min acc. DORNIER, 1984
  SU

(L)

10 g/m3   24 h5) acc. DORNIER, 1984
  SU

(L)

30 g/m3   30 min5) acc. DORNIER, 1984
  YU

(L)

5 g/m3   24 h acc. DORNIER, 1984
  YU

(L)

20 g/m3   30 min acc. DORNIER, 1984
Workp D

L

2 mg/m3 MAK 8 h mean DFG, 1989
Workp D

L

3 ml/m3 MAK 8 h mean DFG, 1989
Workp USA

(L)

2.5 mg/m3 TLV-C Ceiling value ACGIH, 1986
Workp USA

(L)

2 ppm TLV-C Ceiling value ACGIH, 1986
Workp D

L

4 mg/g (aqu) BAT Urine11) DFG, 1988
  D

G

1 g/m3   1 d, plants6) VDI, 1987
  D

G

0.25 g/m3   1 mon, plants6) VDI, 1987
  D

G

0.15 g/m3   7 mon, plants6) VDI, 1987
  D

G

2 g/m3   1 d, plants7) VDI, 1987
  D

G

0.6 g/m3   1 mon, plants7) VDI, 1987
  D

G

0.4 g/m3   7 mon, plants7) VDI, 1987
  D

G

6 g/m3   1 d, plants8) VDI, 1987
  D

G

1.8 g/m3   1 mon, plants8) VDI, 1987
  D

G

1.2 g/m3   7 mon, plants8) VDI, 1987
  USA

G

2.7 g/m3   1 d, pesticide acc. ULLMANN, 1985
  USA

G

0.78 g/m3   1 mon, pesticide acc. ULLMANN, 1985
  USA

G

0.5 g/m3   Vegetat. period acc. ULLMANN, 1985
Foodstuffs:
Working animals Fodder D

L

30 mg/kg (88% DS)   9) acc. BAFEF, 1987
Fodder D

L

50 mg/kg   10) acc. BAFEF, 1987
Fodder D

L

100 mg/kg   Pigs acc. BAFEF, 1987
Fodder D

L

350 mg/kg   Poultry acc. BAFEF, 1987
Fodder D

L

150 mg/kg   Other animals acc. BAFEF, 1987

Notes:

1) For industrial and business conurbations
2) For residential and rural areas
3) For protected areas
4) For specially protected areas
5) For residential areas
6) Highly sensitive plants
7) Sensitive plants
8) Less sensitive plants
9) Lactating cattle, sheep, goats
10) Other cattle, sheep, goats
11) HF and ist inorganic gaseous compounds, stated as F
12) F and ist vapourous/gaseous compounds, stated as HF

Assessment/comments

When released into the atmosphere, hydrogen fluoride can prove to be a potent plant killer. Therefore, it should only be released in small quantities. Numerous limit values for differing exposure periods were established by the VDI in 1987.
The addition of fluoride to drinking water is the subject of debate. It has been proven beyond doubt that a lack of fluorine is harmful to the teeth, but the absorption of major quantities of fluorine is harmful to both humans and animals.
The information available to date does not permit conclusive assessment.


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