Hydrofluoric acid = 불화수소산(弗化水素酸) = 불산(弗酸)

1. 이름: 플루오린화 수소산(HF, Hydrofluoric acid)은 플루오린화 수소의 수용액으로불화수소산(弗化水素酸) 또는 불산(弗酸)이라고도 한다.

2. 화학식: 플루오린화 수소산은 강산으로 분류되는 염산이나 브로민화 수소산 등의 다른 할로젠화 수소들과 달리플루오르와 수소 사이에 강한 수소 결합이 작용하여, 이온화가 잘 일어나지 않아 약산으로 분류된다.

HF + H₂O  H₃O⁺ + F⁻

하지만 플루오린화 수소의 농도가 높아지면 산도가 급격히 높아진다.

2 HF  H⁺ + FHF⁻

3. 용도: 유리와 금속을 녹이기 때문에, 플루오린화 수소산은 플라스틱병에 보관한다.

SiO₂ + 4 HF → SiF₄ (g) + 2 H₂O

SiO₂ + 6 HF → H₂SiF₆ + 2 H₂O

4. 독성: 신체에 닿을 경우 플루오린화 수소가 신체의 수분과 수소 결합을 하면서, 뼈 속까지 침투하여 심하면 신체를 절단해야하는 상황까지 이르게할 수 있는 굉장히 유독한 산이다.

플루오린화 수소산에 의한 화상

5. 유럽 연합 위험 규정:  (영어: R-phrases, Risk Phrases) - (1) R26/27/28: 흡임/삼킴/피부 접촉시 매우 유독함. (2) R35: 매우 심각한 화상의 원인이 됨

6. 물리적 성질: 상태 - 액체; 원자량 - 20 (HF) g/mol; 밀도 - 1.15 g/cm3; 형태 - 무색

7. 일반적인 성질: 이름-플루오린화 수소산; IUPAC 이름-Hydrofluoric acid; 화학식-HF의 수화물; 별칭-fluoric acid; fluorhydric acid; CAS 번호-7664-39-3 (CAS 등록 번호(Chemical Abstract Service)는 이제까지 알려진 모든 화합물, 중합체 등을 기록하는 번호이다. 미국 화학회 American Chemical Society에서 운영하는 서비스이며, 모든 화학 물질을 중복 없이 찾을 수 있도록 한다.)

8. 불산, 치약에 들어간 불소하고 다른건가?

지난 9월 27일 경북 구미시 산동면에서 불산가스 누출사고가 발생했다. 그 결과 5명이 사망하고 반경 700m 이내 지역의 숲과 들이 초토화됐다. 부작용도 심각해 마을 주민 수백 명이 두통과 메스꺼움에 시달리고 있으며 가축들도 비정상적인 행동을 보이고 있다고 한다. 도대체 불산가스가 뭔데 이런 무서운 결과를 가져왔을까.

불산(불화수소산, hydrofluoric acid)은 불화수소(hydrogen fluoride)를 물에 녹인 것이다. 따라서 이번 사고의 원인을 엄밀히 말하면 불화수소가스다. 불화수소는 수소원자 하나와 불소원자 하나가 만나 만들어진 분자로(분자식 HF), 끓는점이 섭씨 19.5도로 액화되기 쉽다. 불화수소는 물과 잘 섞이기 때문에 가스를 마시면 기관지와 폐 조직에 금방 흡수돼 불산이 된다. 

불산의 구성 원소 가운데 하나인 불소는 우리에게 익숙하다. 바로 치약 때문이다. 하지만 불소만큼 화학자들을 애먹인 원소도 없다. 불소 연구의 출발점은 16세기 형석 발견으로 거슬러 올라간다. 

독일 광물학자인 게오르기우스 아그리콜라는 금속 제련을 쉽게 해주는 광물을 발견해 ‘플루오레스(fluores)’라는 이름을 붙였다. ‘흐른다’는 뜻의 라틴어 ‘fleure’에서 따온 말로 이 광물은 비교적 낮은 온도에서도 녹아 흘러내렸기 때문이다. 뒤에 이 광물의 이름이 ‘fluorspar’ 또는 ‘fluorite’, 즉 형석이 됐다.

17세기 독일의 유리장인인 하인리히 슈반하드는 유리병에 담은 황산용액에 형석을 넣자 유리가 뿌옇게 되는 것을 발견했다. 그는 이 현상을 이용해 유리표면을 가공할 때 이 용액을 썼다. 18세기 스웨덴의 화학자 카를 셸레는 슈반하드의 발견을 면밀히 검토했는데, 그 결과 이 용액이 유리를 부식시킨다고 결론 내렸다. 그는 형석이 황산에 녹으면서 어떤 산으로 바뀐다고 추측하고 이를 ‘불산’이라 불렀다.

이후 불산은 점차 화학자들의 관심을 끌었는데 프랑스의 과학자 앙드레-마리 앙페르도 그 중 한명이었다. 1810년 앙페르는 불산의 특성이 염산과 비슷한 점이 있다는 것을 발견하고 여기에는 염소와 비슷한 미지의 원소가 들어있다고 확신했다. 그는 형석이 칼슘과 이 미지의 원소로 이뤄져 있다고 추측했다(훗날 형석의 화학식이 CaF2로 밝혀졌다!).

앙페르는 자신의 생각을 당시 최고의 화학자였던 영국의 험프리 데이비에게 편지로 알렸고 처음에는 반신반의하던 데이비도 결국은 수긍해 1811년 이 미지의 원소를 fluorite(형석)에서 따와 ‘fluorine(불소)’이라고 명명했다. 

이제 남은 과제는 불소를 순수한 상태로 분리해서 정말 새로운 원소임을 입증하는 것이었다. 앙페르와 데이비는 물론 많은 화학자들이 실험에 뛰어들었지만 모두 실패했다. 불소는 워낙 반응성이 커서 불소분자(F2)가 만들어지자마자 금방 다른 원소와 반응해 불소이온(F-)의 염(salt)으로 바뀌기 때문이다.

결국 불산으로 실험하던 화학자들은 몸이 상하거나 심지어 죽기도 했다. 앙페르도 불산 실험으로 몸이 상했고, 실험을 많이 했던 데이비는 눈과 손가락을 다쳐 고생했다. 프랑스의 화학자 제롬 니클레는 불산가스를 과도하게 흡입해 목숨을 잃었다. 이렇게 불소를 분리하려다가 죽은 화학자들을 기려 ‘불소 순교자(fluorine martyrs)’라고 부르기도 한다. 

불소 분리의 영예는 프랑스의 화학자 앙리 무아상에게 돌아갔다. 1886년 무아상은 전기분해를 이용해 불소(F2)기체를 얻는데 성공했다. 백금과 이리듐의 합금이 불소의 공격을 견딘다는 것을 운 좋게 발견해 이 합금을 전극으로 쓴 결과다. 이 업적으로 무아상은 1906년 노벨 화학상을 받았다. 

그런데 불산이 우리 몸에 들어와 어떤 일을 벌이기에 이런 무시무시한 결과로 이어지는 걸까. 일부 언론에서는 불산이 황산이나 염산처럼 강산이기 때문에 독성을 띠는 것처럼 설명하지만, 사실 불산 자체는 강산이 아니다. 다만 농도가 높아질수록 산성이 급속도로 커진다. 불산이 위험한 건 오히려 산성이 크지 않아서이다. 불화수소(HF) 대부분이 불소이온(F-)으로 해리되지 않아 조직에 침투하기 쉽기 때문이다. 세포막은 지질이기 때문에 이온은 잘 통과하지 못한다.

따라서 불산 농도가 아주 높지 않다면 처음 접했을 때는 증상이 그렇게 심하지 않다. 불소 누출사고에서 시간이 지날수록 환자들이 늘어나는 것도 이런 이유 때문으로 보인다. 처음에는 괜찮은 것 같았는데 하루 이틀 지나자 몸에 이상이 느껴졌을 것이다. 

불산이 혈액과 조직으로 침투하면 작업을 시작한다. 체내에 들어온 불산의 일부는 수소이온과 불소이온으로 해리되는데, 불소이온이 체내 칼슘이온(Ca2+)이나 마그네슘이온(Mg2+)을 만나 불용성 염을 만든다. 이렇게 불소이온이 소모되면 불산이 또 해리되고 이런 과정이 반복되며 결국 불산이 전부 해리된다. 

불소이온이 뼈에 들어가면 뼈 속 칼슘을 빼낸다. 불소이온과 뼈의 칼슘이온이 만나 생기는 염의 화학식은 CaF2, 바로 형석이다. 결국 우리 몸 안에 미세한 돌가루가 쌓이는 셈이다. 게다가 체내 칼슘이온과 마그네슘이온 농도가 떨어지면서 몸에 이상이 생긴다. 특히 체내에서 중요한 생리작용을 하는 칼슘이온이 결핍되면 심각한 결과로 이어지게 된다. 

한마디로 칼슘이온은 다양한 생체신호를 전달하는 고리다. 세포끼리 붙어있게 하는데도 관여하며, 혈액 내 칼슘이온 농도는 신경세포의 활동에 영향을 준다. 갑자기 불산이 체내로 들어와 칼슘이온이 극단적으로 떨어지면 호흡근육이 굳어져 질식사한다. 때문에 인체는 체내 칼슘이온농도를 엄격하게 조절하는 복잡한 메커니즘으로 운영되고 있다. 

지금까지 얘기를 보면 불소는 절대 우리 몸에 들어와서는 안 되는 원소처럼 보이지만 사실 우리 몸에는 불소가 꽤 존재한다. 물론 불소이온 또는 그 염의 형태로 말이다. 혈액의 불소 농도는 0.5ppm(1ppm은 100만 분의 1) 정도이고 연조직은 0.05ppm 정도 된다. 뼈에는 무려 200~1200ppm이 들어 있어 다 합치면 3~6그램이나 된다. 

실제로 불소는 우리 몸이 건강하기 위해 꼭 있어야 한다. 불소의 독성은 불소 자체의 특성이 아니라 불소가 과잉으로 몸에 들어왔을 때 일어나는 일인 것이다. 우리 몸에 있는 불소 대부분은 뼈와 이에 들어있다. 뼈는 무기질 성분이 45% 정도인데 무기질의 주성분은 칼슘과 인산으로 이루어진 염(인산칼슘)이다. 여기에 불소가 섞여 들어가면 인산칼슘 일부를 불화인회석(fluoroapatite)로 바꾸고, 그 결과 뼈가 튼튼해진다. 

200여 년 전 불산을 연구하다 새로운 원소의 존재를 확신한 앙페르는 자신의 편지에 동의한 데이비가 명명한, 플루오라이트(형석)에서 따온 플루오린(불소)이란 원소명 대신 다른 이름을 제안했다. 그러나 “그냥 가자”는 당대 최고 화학자 데이비의 반응에 포기해야 했다. 불산을 연구하다 혼쭐이 난 앙페르가 제안한 원소 이름은 ‘프쏘린(phthorine)’으로 그리스어 ‘프쏘로스(phthoros)’에서 따왔다. 프쏘로스는 ‘파괴하다’라는 뜻이다.

강석기 과학칼럼니스트

http://www.osha.gov/SLTC/healthguidelines/hydrogenfluoride/recognition.html

Occupational Safety and Health Guideline for Hydrogen Fluorid

DISCLAIMER: 

These guidelines were developed under contract using generally accepted secondary sources. The protocol used by the contractor for surveying these data sources was developed by the National Institute for Occupational Safety and Health (NIOSH), the Occupational Safety and Health Administration (OSHA), and the Department of Energy (DOE). The information contained in these guidelines is intended for reference purposes only. None of the agencies have conducted a comprehensive check of the information and data contained in these sources. It provides a summary of information about chemicals that workers may be exposed to in their workplaces. The secondary sources used for supplements III and IV were published before 1992 and 1993, respectively, and for the remainder of the guidelines the secondary sources used were published before September 1996. This information may be superseded by new developments in the field of industrial hygiene. Therefore readers are advised to determine whether new information is available.

Introduction

This guideline summarizes pertinent information about hydrogen fluoride for workers and employers as well as for physicians, industrial hygienists, and other occupational safety and health professionals who may need such information to conduct effective occupational safety and health programs. Recommendations may be superseded by new developments in these fields; readers are therefore advised to regard these recommendations as general guidelines and to determine whether new information is available.

Recognition

SUBSTANCE IDENTIFICATION 

* Formula 
HF 
* Structure 
(For Structure, see paper copy) 
* Synonyms 
Anhydrous hydrofluoric acid, antisal 2B, hydrofluoride, hydrofluoric acid, fluorhydric acid, fluoric acid 
* Identifiers

1. CAS No.: 7664-39-3
2. RTECS No.: MW7875000; (also listed as MW7890000)
3. DOT UN: 1052 15 (anhydrous), 1790 59 (solution)
4. DOT label: Corrosive, poison (anhydrous)

* Appearance and odor 

Hydrogen fluoride is a colorless, fuming liquid or gas (depending on the temperature) with a strong, irritating odor. The air odor threshold for hydrogen fluoride is 0.042 part per million (ppm) parts of air. 

CHEMICAL AND PHYSICAL PROPERTIES 

* Physical data

1. Molecular weight: 20.01
2. Boiling point (at 760 mm Hg): 19.51 degrees C (67.2 degrees F)
3. Specific gravity: 0.987 at 20 degrees C (68 degrees F)
4. Vapor density: 0.92
5. Melting point: -83.1 degrees C (-117.58 degrees F)
6. Vapor pressure at 2.5 degrees C (36.5 degrees F): 400 mm Hg
7. Solubility: Very soluble in water, in alcohol, and in most organic solvents; slightly soluble in ether.
8. Evaporation rate: Data not available.

* Reactivity 

Conditions contributing to instability: Exposure to moisture or steam may produce highly explosive hydrogen gas. Reactions may also occur in the presence of heat and light.

1. Incompatibilities: Contact between hydrogen fluoride and metals, concrete, glass, strong bases, sodium hydroxide, potassium hydroxide, and ceramics may result in reactions.
2. Hazardous decomposition products: Toxic gases and vapors such as fluorine may be released in a fire involving hydrogen fluoride.
3. Special precautions: Store in containers composed of non-corrosive materials, such as lead and wax. The corrosive action on metals can result in the formation of hydrogen gas.

* Flammability 

Hydrogen fluoride is a nonflammable gas. 

The National Fire Protection Association has assigned a flammability rating of 0 (minimal fire hazard) to hydrogen fluoride.

1. Flash point: Not applicable.
2. Autoignition temperature: Not applicable.
3. Flammable limits in air: Not applicable.
4. Extinguishant: For small fires use dry chemical or carbon dioxide for fires that include anhydrous hydrogen fluoride. For small fires that involve the hydrogen fluoride solution use dry chemical, carbon dioxide, water spray or regular foam. Use water spray, fog, or regular foam to fight large fires involving both phases of hydrogen fluoride. 
   
   Fires involving hydrogen fluoride should be fought upwind from the maximum distance possible. Keep unnecessary people away; isolate the hazard area and deny entry. Isolate the area for at least 150 feet in all directions until gas has dispersed. Emergency personnel should stay out of low areas and ventilate closed spaces before entering. Containers of hydrogen fluoride may explode in the heat of the fire and should be moved from the fire area if it is possible to do so safely. If this is not possible, cool fire exposed containers from the sides with water until well after the fire is out. Do not get water inside the containers. Stay away from the ends of containers. Firefighters should wear a full set of chemical protective clothing and self-contained breathing apparatus when fighting fires involving hydrogen fluoride.

EXPOSURE LIMITS 

* OSHA PEL 

The current Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) for hydrogen fluoride is 3 ppm() as an 8-hour time-weighted average (TWA) concentration [29 CFR 1910.1000, Table Z-2]. 

* NIOSH REL 

The National Institute for Occupational Safety and Health (NIOSH) has established a recommended exposure limit (REL) for hydrogen fluoride of 3 ppm (2.5 mg/m(3)) as a TWA for up to a 10-hour workday and a 40-hour workweek and a short-term exposure limit (STEL) of 6 ppm (5 mg/m(3)) [NIOSH 1992]. NIOSH also applies a skin notation, which indicates that hydrogen fluoride is capable of systemic toxicity and direct adverse effects on the skin following dermal exposure [NIOSH 2011].

* ACGIH TLV 

The American Conference of Governmental Industrial Hygienists (ACGIH) has assigned hydrogen fluoride an 8 hour threshold limit value (TLV) of 0.5 ppm (0.4 mg/m(3)) and a ceiling limit value of 2 ppm (1.7 mg/m(3)), which should not be exceeded during any part of the working exposure [ACGIH 2005]. 

* Rationale for Limits 

The NIOSH limit is based on the risk of skin, eye, and airway irritation; and on effects on bone tissue [NIOSH 1992]. 

The ACGIH limit is based on the risk of irritation [ACGIH 1991, p. 781].

Evaluation

HEALTH HAZARD INFORMATION 

* Routes of Exposure 

Exposure to hydrogen fluoride and its aqueous solution can occur through inhalation, ingestion, and eye or skin contact [Sittig 1991, p. 909]. 

* Summary of toxicology

1. Effects on Animals: Hydrogen fluoride is a severe pulmonary irritant as a gas; as a liquid, it is corrosive to the skin and eyes. The 1-hour LC(50)s in rats, mice, and monkeys are 1,276 ppm, and 1,774 ppm, respectively [Sax and Lewis 1989]. Rats, rabbits, guinea pigs, and dogs experienced irritation of the conjunctivae, nasal tissues, and respiratory system after acute inhalation exposures at near-lethal levels. Pathological lesions were observed in the kidney and liver, and the severity of the lesions was dose related. The external nares and nasal vestibules were black, and, at dosages causing considerable mortality, those areas showed zones of mucosal and submucosal necrosis. The skin of animals exposed at lethal concentrations showed superficial subcutaneous and deep dermal zones of acute inflammation. The hair of these animals could be pulled out with ease and skin ruptured under minimal tension [Clayton and Clayton 1982]. Experiments in which a 20-percent aqueous solution was instilled into the eyes of rabbits caused immediate damage in the form of total corneal opacification and conjunctival ischemia; within an hour, corneal stroma edema occurred, followed by necrosis of anterior ocular structures [Grant 1986]. Subacute, 30-day exposures at 30 ppm caused moderate hemorrhage and edema of the lungs in dogs, rabbits, and rats. At autopsy, rats showed renal cortical degeneration and necrosis, and dogs had ulceration of the scrotum. Exposures at 5.5 ppm under the same conditions produced localized hemorrhage in the lung in one of five dogs, but no changes were observed in the rabbit or rat [Clayton and Clayton 1982]. Hydrogen fluoride has also produced reproductive, teratogenic, and mutagenic effects in experimental animals [NIOSH 1991].
2. Effects on Humans: In humans, inhalation of hydrogen fluoride gas may cause immediate or delayed-onset pulmonary edema after a 1-hour exposure [Hathaway et al. 1991]. In addition, exposure to high concentrations of the vapors of hydrofluoric acid characteristically results in ulcerative tracheobronchitis and hemorrhagic pulmonary edema; this local reaction is equivalent to that caused by gaseous hydrogen chloride [Gosselin 1984]. From accidental, occupational, and volunteer exposures, it is estimated that the lowest lethal concentration for a 5-minute human exposure to hydrogen fluoride is in the range of 50 to 250 ppm [Hathaway et al. 1991]. Significant exposures by dermal or inhalation route may cause hypocalcemia and hypomagnesemia; cardiac arrhythmias may follow. Acute renal failure has also been documented after an ultimately fatal inhalation exposure [Hathaway et al. 1991]. Repeated exposure to excessive concentrations of fluoride over a period of years results in increased density of bone and eventually may cause crippling fluorosis (osteosclerosis caused by the deposition of fluoride in bone) [Hathaway et al. 1991]. Percutaneous absorption of pure liquefied hydrogen fluoride gas (chilled and under pressure until the vessel burst) produced severe hypocalcemia, multiple attacks of ventricular fibrillation, and death 9.5 hours after exposure. Skin contact with hydrogen fluoride or solutions containing more than 30 percent hydrogen fluoride produces immediate pain; reactions to more dilute solutions may be delayed for many hours. The accompanying pain is excruciating and persistent, and healing is delayed [Gosselin 1984]. Severe eye injuries may occur from splashes. Liquefied hydrogen fluoride gas has been known to destroy the eye and to require enucleation; the severity of burns from the aqueous solution depends on the concentration [Grant 1986]. Ingestion of an estimated 1.5 grams of hydrofluoric acid produces sudden death; however, repeated ingestion of small amounts of hydrogen fluoride may cause fluoride osteosclerosis [Gosselin 1984].

* Signs and symptoms of exposure

1. Acute exposure: Acute inhalation exposures result from hydrogen flouride gas and fumes from concentrated hydrogen flouride liquid. Inhalation can produce severe eye, nose, and throat irritation; delayed fever, cyanosis, and pulmonary edema; and may cause death. Contact of the skin with the liquid can permit the flouride ion to penetrate deep into the tissue causing localized necrosis and systemic toxicity [Hathaway et al. 1991, NIOSH 2011]. Ingestion causes destruction of the tissues of the digestive tract, severe irritation of the respiratory tract, and will likely lead to systemic toxicity [NLM 1992].
2. Chronic exposure: Chronic exposure to low airborne concentrations may cause nasal congestion and bronchitis. Repeated exposure to excessive hydrogen fluoride concentrations causes fluorosis; the early signs of increased bone density from fluoride deposition are most apparent in the lumbar spine and pelvis and can be detected by roentgenograph [NLM 1992].

EMERGENCY MEDICAL PROCEDURES 

* Emergency medical procedures: [NIOSH to supply] Rescue: Remove an incapacitated worker from further exposure and implement appropriate emergency procedures (e.g., those listed on the Material Safety Data Sheet required by OSHA's Hazard Communication Standard [29 CFR 1910.1200]) which will likely involve immediate consulation with emergency hospital care. All workers should be familiar with emergency procedures, the location and proper use of emergency equipment, and methods of protecting themselves during rescue operations. Bystanders may be exposed to hydrogen flouride from off gassing of the spill and the exposed worker. 

EXPOSURE SOURCES AND CONTROL METHODS 

The following operations may involve hydrogen fluoride and lead to worker exposures to this substance:

• The manufacture and transportation of hydrogen fluoride
• Use in manufacture of chlorofluorohydrocarbons for application as refrigerant fluids, aerosol propellants, specialty solvents, high-performance plastics, and foaming agents
• Use (as aqueous acid) in cleaning sandstone and marble, as a pickling agent for stainless steel and other metals, and as a cleaner in the meat packing industry
• Use (as anhydrous acid) in manufacture of aluminum fluoride and synthetic cryolite to reduce aluminum oxide to aluminum
• Use (as aqueous acid) in electroplating operations
• Liberated during manufacture of fertilizer and the burning of coal
• Use (as anhydrous acid) as a catalyst in alkylation of petroleum fractions to produce high-octane fuels
• Use (as aqueous acid) in etching, frosting, and polishing of glassware and ceramics
• Use as an acidizing agent during injection of acid into oil wells
• Used (as aqueous acid) in removal of sand and scale from foundry castings
• Use (as anhydrous acid) in separation and purification of uranium isotopes
• Use (as aqueous acid) in treating textiles to remove trace metals and in preparation of microelectronic circuits and quartz crystals for radio oscillators
• Use (as anhydrous acid) in production of fluorosilicone products
• Use (as anhydrous acid) in manufacture of pharmaceuticals and special dyes
• Use to arrest fermentation in brewing and for etching silicon wafers in semi-conductor manufacture, for purification of filter paper and graphite, in enamelling and galvanizing iron, and to increase the porosity of ceramics

Methods that are effective in controlling worker exposures to hydrogen fluoride, depending on the feasibility of implementation, are as follows:

• Process enclosure
• Local exhaust ventilation
• General dilution ventilation
• Personal protective equipment

Workers responding to a release or potential release of a hazardous substance must be protected as required by paragraph (q) of OSHA's Hazardous Waste Operations and Emergency Response Standard [29 CFR 1910.120]. 

Good sources of information about control methods are as follows:

1. ACGIH [1992]. Industrial ventilation--a manual of recommended practice. 21st ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.
2. Burton DJ [1986]. Industrial ventilation--a self study companion. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.
3. Alden JL, Kane JM [1982]. Design of industrial ventilation systems. New York, NY: Industrial Press, Inc.
4. Wadden RA, Scheff PA [1987]. Engineering design for control of workplace hazards. New York, NY: McGraw-Hill.
5. Plog BA [1988]. Fundamentals of industrial hygiene. Chicago, IL: National Safety Council.

MEDICAL SURVEILLANCE 

OSHA is currently developing requirements for medical surveillance. When these requirements are promulgated, readers should refer to them for additional information and to determine whether employers whose employees are exposed to hydrogen fluoride are required to implement medical surveillance procedures. 

* Medical Screening 

Workers who may be exposed to chemical hazards should be monitored in a systematic program of medical surveillance that is intended to prevent occupational injury and disease. The program should include education of employers and workers about work-related hazards, early detection of adverse health effects, and referral of workers for diagnosis and treatment. The occurrence of disease or other work-related adverse health effects should prompt immediate evaluation of primary preventive measures (e.g., industrial hygiene monitoring, engineering controls, and personal protective equipment). A medical surveillance program is intended to supplement, not replace, such measures. To detect and control work-related health effects, medical evaluations should be performed (1) before job placement, (2) periodically during the term of employment, and (3) at the time of job transfer or termination. 

* Preplacement medical evaluation 

Before a worker is placed in a job with a potential for exposure to hydrogen fluoride, a licensed health care professional should evaluate and document the worker's baseline health status with thorough medical, environmental, and occupational histories, a physical examination, and physiologic and laboratory tests appropriate for the anticipated occupational risks. These should concentrate on the function and integrity of the skin, eyes, liver, kidneys, and respiratory system. Medical surveillance for respiratory disease should be conducted using the principles and methods recommended by the American Thoracic Society. 

A preplacement medical evaluation is recommended to assess medical conditions that may be aggravated or may result in increased risk when a worker is exposed to hydrogen fluoride at or below the prescribed exposure limit. The health care professional should consider the probable frequency, intensity, and duration of exposure as well as the nature and degree of any applicable medical condition. Such conditions (which should not be regarded as absolute contraindications to job placement) include a history and other findings consistent with diseases of the skin, eyes, liver, kidneys, and respiratory system. 

* Periodic medical evaluations 

Occupational health interviews and physical examinations should be performed at regular intervals during the employment period, as mandated by any applicable Federal, State, or local standard. Where no standard exists and the hazard is minimal, evaluations should be conducted every 3 to 5 years or as frequently as recommended by an experienced occupational health physician. Additional examinations may be necessary if a worker develops symptoms attributable to hydrogen fluoride exposure. The interviews, examinations, and medical screening tests should focus on identifying the adverse effects of hydrogen fluoride on the skin, eyes, liver, kidneys, or respiratory system. Current health status should be compared with the baseline health status of the individual worker or with expected values for a suitable reference population. 

* Termination medical evaluations 

The medical, environmental, and occupational history interviews, the physical examination, and selected physiologic or laboratory tests that were conducted at the time of placement should be repeated at the time of job transfer or termination to determine the worker's medical status at the end of his or her employment. Any changes in the worker's health status should be compared with those expected for a suitable reference population. 

* Biological monitoring 

Biological monitoring involves sampling and analyzing body tissues or fluids to provide an index of exposure to a toxic substance or metabolite. The fluoride concentration in urine is a useful index for exposure to hydrogen fluoride and has been found to average about 4 mg/liter in an end-of-shift specimen following an 8-hour exposure to 3 ppm hydrogen fluoride. Analysis of the specimens is conducted by direct measurement of inorganic fluoride using a fluoride-specific electrode. 

WORKPLACE MONITORING AND MEASUREMENT 

Determination of a worker's exposure to airborne hydrogen fluoride is made using a mixed cellulose ester filter (MCEF) 0.8 microns, a filter spacer, and a Na(2)CO(3) impregnated back-up pad in a three piece filter cassette. Samples are collected at a maximum flow rate of 1.5 liters/minute (TWA or STEL) until a maximum collection volume of 90 liters is reached. Analysis is conducted by using an ion-specific electrode (ISE). This method (OSHA ID 110) is partially validated and is described in the OSHA Computerized Information System [OSHA 1994] and in NIOSH Method No. 7903 (inorganic acids) [NIOSH 1994b].

Controls

PERSONAL HYGIENE PROCEDURES 

If hydrogen fluoride contacts the skin, workers should flush the affected areas immediately with plenty of water, followed by washing with soap and water. The exposed workers should then seek emergency hospital treatment where they may be treated for delayed effects from contacting hydrogen flouride. 

Clothing contaminated with hydrogen fluoride should be removed immediately, and provisions should be made for the safe removal of the chemical from the clothing. Persons laundering the clothes should be informed of the hazardous properties of hydrogen fluoride, particularly its potential for causing irritation. 

A worker who handles hydrogen fluoride should thoroughly wash hands, forearms, and face with soap and water before eating, using tobacco products, using toilet facilities, applying cosmetics, or taking medication. 

Workers should not eat, drink, use tobacco products, apply cosmetics, or take medication in areas where hydrogen fluoride or a solution containing hydrogen fluoride is handled, processed, or stored. 

STORAGE 

Hydrogen fluoride should be stored in a cool, dry, well-ventilated area in tightly sealed containers that are labeled in accordance with OSHA's Hazard Communication Standard [29 CFR 1910.1200]. Containers of hydrogen fluoride should be protected from physical damage and should be stored separately from metals, concrete, glass, strong bases, sodium hydroxide, potassium hydroxide, and ceramics. 

SPILLS AND LEAKS 

In the event of a spill or leak involving hydrogen fluoride, persons not wearing protective equipment and clothing should be restricted from contaminated areas until cleanup has been completed. The following steps should be undertaken following a spill or leak:

1. Notify safety personnel.
2. Remove all sources of heat and ignition.
3. Ventilate the area of the spill or leak.
4. If source of leak is a cylinder and the leak cannot be stopped in place, remove the leaking cylinder to a safe place in the open air, and repair leak or allow cylinder to empty.
5. If in the liquid form, allow to vaporize and disperse the gas, or cover with sodium carbonate or an equal mixture of soda ash and slaked lime. After mixing, add water, if necessary, to form a slurry.

SPECIAL REQUIREMENTS 

U.S. Environmental Protection Agency (EPA) requirements for emergency planning, reportable quantities of hazardous releases, community right-to-know, and hazardous waste management may change over time. Users are therefore advised to determine periodically whether new information is available. 

* Emergency planning requirements 

Employers owning or operating a facility at which there are 100 pounds or more of hydrogen fluoride must comply with EPA's emergency planning requirements [40 CFR Part 355.30]. 

* Reportable quantity requirements for hazardous releases 

A hazardous substance release is defined by EPA as any spilling, leaking, pumping, pouring, emitting, emptying, discharging, injecting, escaping, leaching, dumping, or disposing into the environment (including the abandonment or discarding of contaminated containers) of hazardous substances. In the event of a release that is above the reportable quantity for that chemical, employers are required to notify the proper Federal, State, and local authorities [40 CFR 355.40]. 

The reportable quantity of hydrogen fluoride is 100 pounds. If an amount equal to or greater than this quantity is released within a 24-hour period in a manner that will expose persons outside the facility, employers are required to do the following: - Notify the National Response Center immediately at (800) 424-8802 or at (202) 426-2675 in Washington, D.C. [40 CFR 302.6]. 

- Notify the emergency response commission of the State likely to be affected by the release [40 CFR 355.40]. 

- Notify the community emergency coordinator to the local emergency planning committee (or relevant local emergency response personnel) of any area likely to be affected by the release [40 CFR 355.40]. 

* Community right-to-know requirements 

Employers who own or operate facilities in SIC codes 20 to 39 that employ 10 or more workers and that manufacture 25,000 pounds or more of hydrogen fluoride per calendar year or otherwise use 10,000 pounds or more of hydrogen fluoride per calendar year are required by EPA [40 CFR Part 372.30] to submit a Toxic Chemical Release Inventory form (Form R) to EPA reporting the amount of hydrogen fluoride emitted or released from their facility annually. 

* Hazardous waste management requirements 

EPA considers a waste to be hazardous if it exhibits any of the following characteristics: ignitability, corrosivity, reactivity, or toxicity as defined in 40 CFR 261.21-261.24. Under the Resource Conservation and Recovery Act (RCRA) [40 USC 6901 et seq.], EPA has specifically listed many chemical wastes as hazardous. Hydrogen fluoride is listed as a hazardous waste under RCRA and has been assigned EPA Hazardous Waste No. U134. This substance has been banned from land disposal until treated by venting compressed gases into an absorbing or reacting media, followed by neutralization. 

Providing detailed information about the removal and disposal of specific chemicals is beyond the scope of this guideline. The U.S. Department of Transportation, EPA, and State and local regulations should be followed to ensure that removal, transport, and disposal of this substance are conducted in accordance with existing regulations. To be certain that chemical waste disposal meets EPA regulatory requirements, employers should address any questions to the RCRA hotline at (703) 412-9810 (in the Washington, D.C. area) or toll-free at (800) 424-9346 (outside Washington, D.C.). In addition, relevant State and local authorities should be contacted for information on any requirements they may have for the waste removal and disposal of this substance. 

RESPIRATORY PROTECTION 

* Conditions for respirator use 

Good industrial hygiene practice requires that engineering controls be used where feasible to reduce workplace concentrations of hazardous materials to the prescribed exposure limit. However, some situations may require the use of respirators to control exposure. Respirators must be worn if the ambient concentration of hydrogen fluoride exceeds prescribed exposure limits. Respirators may be used (1) before engineering controls have been installed, (2) during work operations such as maintenance or repair activities that involve unknown exposures, (3) during operations that require entry into tanks or closed vessels, and (4) during emergencies. Workers should only use respirators that have been approved by NIOSH and the Mine Safety and Health Administration (MSHA). 

* Respiratory protection program 

Employers should institute a complete respiratory protection program that, at a minimum, complies with the requirements of OSHA's Respiratory Protection Standard [29 CFR 1910.134]. Such a program must include respirator selection, an evaluation of the worker's ability to perform the work while wearing a respirator, the regular training of personnel, respirator fit testing, periodic workplace monitoring, and regular respirator maintenance, inspection, and cleaning. The implementation of an adequate respiratory protection program (including selection of the correct respirator) requires that a knowledgeable person be in charge of the program and that the program be evaluated regularly. For additional information on the selection and use of respirators and on the medical screening of respirator users, consult the latest edition of the NIOSH Respirator Decision Logic [NIOSH 1987b] and the NIOSH Guide to Industrial Respiratory Protection [NIOSH 1987a]. 

PERSONAL PROTECTIVE EQUIPMENT 

Workers should use appropriate personal protective clothing and equipment that must be carefully selected, used, and maintained to be effective in preventing skin contact with hydrogen fluoride. The selection of the appropriate personal protective equipment (PPE) (e.g., gloves, sleeves, encapsulating suits) should be based on the extent of the worker's potential exposure to hydrogen fluoride. The resistance of various materials to permeation by 30 to 70 percent solutions of hydrogen fluoride is shown below: 

Material	Breakthrough time (hr)
Saranex	>8
Barricade	>8
Chemrel	>8
Responder	>8
Butyl Rubber	>4
Natural Rubber	Caution 1 to 4
Neoprene	Caution 1 to 4
Polyethylene	Caution 1 to 4
4H (PE/EVAL)	Caution 1 to 4
Nitrile Rubber	<1(*)
Polyvinyl Alcohol	<1(*)
Polyvinyl Chloride	<1(*)

(*) Not recommended, degradation may occur 

To evaluate the use of these PPE materials with hydrogen fluoride, users should consult the best available performance data and manufacturers' recommendations. Significant differences have been demonstrated in the chemical resistance of generically similar PPE materials (e.g., butyl) produced by different manufacturers. In addition, the chemical resistance of a mixture may be significantly different from that of any of its neat components. 

Any chemical-resistant clothing that is used should be periodically evaluated to determine its effectiveness in preventing dermal contact. Safety showers and eye wash stations should be located close to operations that involve hydrogen fluoride. 

Splash-proof chemical safety goggles or face shields (20 to 30 cm long, minimum) should be worn during any operation in which a solvent, caustic, or other toxic substance may be splashed into the eyes. 

In addition to the possible need for wearing protective outer apparel (e.g., aprons, encapsulating suits), workers should wear work uniforms, coveralls, or similar full-body coverings that are laundered each day. Employers should provide lockers or other closed areas to store work and street clothing separately. Employers should collect work clothing at the end of each work shift and provide for its laundering. Laundry personnel should be informed about the potential hazards of handling contaminated clothing and instructed about measures to minimize their health risk. 

Protective clothing should be kept free of oil and grease and should be inspected and maintained regularly to preserve its effectiveness. 

Protective clothing may interfere with the body's heat dissipation, especially during hot weather or during work in hot or poorly ventilated work environments. 

References

ACGIH [1991]. Documentation of the threshold limit values and biological exposure indices. 6th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists. 

ACGIH [2005]. Documentation of threshold limit value for hydrogen flouride. Cincinnati, OH: American Conference of Governmental Industrial Hygienists. 

Amoore JE, Hautala E [1983]. Odor as an aid to chemical safety: odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution. J of App Tox 3(6):272-290. 

ATS [1987]. Standardization of spirometry -- 1987 update. American Thoracic Society. Am Rev Respir Dis 136:1285-1296. 

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DOT [1993]. 1993 Emergency response guidebook, guides 15, 59. Washington, DC: U.S. Department of Transportation, Office of Hazardous Materials Transportation, Research and Special Programs Administration. 

Forsberg K, Mansdorf SZ [1993]. Quick selection guide to chemical protective clothing. New York, NY: Van Nostrand Reinhold. 

Genium [1987]. Material safety data sheet No. 6. Schenectady, NY: Genium Publishing Corporation. 

Gosselin RE, Smith RP, Hodge HC [1984]. Clinical toxicology of commercial products. 5th ed. Baltimore, MD: Williams & Wilkins. 

Grant WM [1986]. Toxicology of the eye. 3rd ed. Springfield, IL: Charles C Thomas. 

Hathaway GJ, Proctor NH, Hughes JP, and Fischman ML [1991]. Proctor and Hughes' chemical hazards of the workplace. 3rd ed. New York, NY: Van Nostrand Reinhold. 

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Mickelsen RL, Hall RC [1987]. A breakthrough time comparison of nitrile and neoprene glove materials produced by different glove manufacturers. Am Ind Hyg Assoc J 48(11): 941-947. 

Mickelsen RL, Hall RC, Chern RT, Myers JR [1991]. Evaluation of a simple weight-loss method for determining the permeation of organic liquids through rubber films. Am Ind Hyg Assoc J 52(10): 445-447. 

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NIOSH [1987b]. NIOSH respirator decision logic. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 87-108. 

NIOSH [1991]. Registry of toxic effects of chemical substances: Hydrogen Fluoride. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, Division of Standards Development and Technology Transfer, Technical Information Branch. 

NIOSH [1992]. Recommendations for occupational safety and health: Compendium of policy documents and statements. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 92-100. 

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NIOSH [1994b]. NIOSH manual of analytical methods. 4th ed. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 94-113. 

NIOSH [2011]. NIOSH Skin Notation Profiles: Hydrogen Fluoride / Hydrofluoric Acid. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2011-137. 

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Partially Updated: 12/12/2012