# I. RECOMMENDATIONS FOR CYANIDE STANDARDS
The National Institute for Occupational Safety and Health recommends that employee exposure to hydrogen cyanide (HCN) and the cyanide salts in the workplace be controlled by adherence to the following sections. The standards are designed to protect the health of workers for up to a 10-hour workday, and a 40-hour workweek over a working lifetime. Compliance with the standard should therefore prevent adverse effects of HCN and cyanide salts on the health of workers. The standards are measurable by techniques that are valid, reproducible, and available to industry and government agencies.
Sufficient technology exists to permit compliance with the recommended standards. The standards will be subject to review and revision as necessary.
These criteria and recommended standards apply to occupational exposure of workers to HCN and cyanide salts. Synonyms for HCN are hydrocyanic acid, prussic acid, and formonitrile. For the purpose of this document, cyanide salts are defined as sodium cyanide (NaCN), potassium cyanide (KCN), or calcium cyanide (Ca(CN)2). The word, cyanide, or the symbol, "CN", is used to designate salts as well as hydrogen cyanide.
The "action level" for hydrogen cyanide or a cyanide salt is defined as one-half the corresponding recommended ceiling environmental exposure limit. "Occupational exposure" to these compounds is defined as exposure to airborne concentrations greater than the corresponding action levels.
The criteria and recommended standards apply to any area in which HCN, any of the cyanide salts or materials containing any of them, alone or in combination with other substances, is used, produced, packaged, processed, mixed, blended, handled, stored in large quantities, or applied.
Exposure to cyanide at concentrations less than or equal to the respective action levels will not require adherence to the recommended standards except for sections 2-7, and 8(c). If "exposure" to other chemicals also occurs, for example to a combination of cyanide and methyl alcohol, provisions of any applicable standards for such other chemicals shall be followed also.

# Section 1 -Environmental (Workplace Air) (a) Concentration
Employee exposure to HCN shall be controlled so as not to exceed 5 milligrams per cubic meter of air expressed as CN (4.7 ppm), determined as a ceiling concentration based on a 10-minute sampling period.
Employee exposure to cyanide salts shall be controlled so as not to exceed 5 milligrams per cubic meter of air expressed as CN, determined as a ceiling value based upon a 10-minute sampling period.
Whenever the air is analyzed for cyanide salts, a concurrent analysis shall be made for HCN. Neither of the respective ceiling values may be exceeded nor may the combined values exceed 5 mg/cu m measured as CN during a 10-minute sampling period.

# (b) Sampling and Analysis
Procedures for sampling, calibration of equipment, and analysis of air samples for HCN and cyanide salts shall be as provided in Appendices I and II, or by any method shown to be equivalent in precision, accuracy and sensitivity to those specified. A sampling period of about 10 minutes is necessary to provide an amount of cyanide readily amenable to analysis by the cyanide selective electrode.
Section 2 -Medical Medical surveillance shall be made available as specified below for all workers occupationally exposed to HCN or cyanide salts.
(a) Preplacement and annual medical examinations shall include:
(1) An initial or interim work and medical history with special attention to skin disorders and those non-specific symptoms, such as headache, nausea, vomiting, dizziness or weakness, that may be associated with chronic exposure.
(2) A physical examination giving particular attention to skin, thyroid, and the cardiovascular and upper respiratory systems.
(3) An evaluation of the advisability of the worker's use of negative-or positive-pressure respirators.
(b) Initial medical examinations shall be made available to presently employed workers within six months of the promulgation of a standard.

# (c)
The responsible physician and the employer shall be aware of the material contained in Appendix V and shall ensure that employees trained in these first-aid measures are on duty whenever there is occupational exposure to HCN or a cyanide salt.
(d) Two physician's treatment kits shall be immediately available to trained medical personnel at each plant where there is a potential for the release of, accidental or otherwise, or for contact with, hydrogen cyanide or cyanide salts. One kit should be portable in order that it may be carried by medical personnel while accompanying a patient to the hospital. The other kit should be kept under lock and key to assure that it is intact and available when and if needed. The key should be readily available at all times to the work supervisor on duty and the storage place should be of such construction as to allow accessibility in the event of loss of the key.
(e) First-aid kits shall be immediately available at workplaces where there is a potential for the release, accidental or otherwise, of hydrogen cyanide or a potential for exposure to cyanide salts. This kit shall contain as a minimum two (2) boxes of ampules (2 dozen), each containing 0.3 ml of amyl nitrite. Ampules shall be replaced biannually or sooner if needed to ensure their potency. The amyl nitrite ampules should be protected from high temperatures. In all cases, the contents of the medical and first-aid kits shall be replaced before the manufacturer's assigned expiration dates. Suggested contents for these kits are listed in Appendix V. In case of contact, immediately flush skin or eyes with plenty of water for at least 15 minutes; get medical attention. Remove contaminated clothing and wash before reuse.

# POISON First Aid
Carry patient to fresh air. Have the patient lie down. Remove contaminated clothing but keep patient warm. Start artificial respiration if breathing stops. Administer antidote (amyl nitrite ampule). Call a physician.

# Temporary Antidote
If cyanide gas is inhaled: Break an amyl nitrite ampule in a cloth and hold lightly under nose for 15 seconds. Repeat at about 15-second intervals.
If cyanide is swallowed:
Break an amyl nitrite ampule in a cloth and hold lightly under nose for 15 seconds.
Repeat inhalation of amyl nitrite 5 times at about 15 second intervals. If patient is conscious or when consciousness returns, give emetic (1 tablespoonful of salt to each glass of warm water) and repeat until vomit fluid is clear. Do not give an emetic to an unconscious or barely conscious person.

# (b)
The following warning sign shall be affixed in a readily visible location at or near entrances to areas containing HCN and where there is reasonable potential for emergencies: (1) location of gas masks and other emergency equipment,
(2) instructions for sounding emergency alarm,
(3) location of first-aid equipment and supplies, and
(4) instructions for summoning medical aid.)
The sign shall be printed both in English and in the predominant language of non-English-reading workers. All workers shall receive training and information on the hazards and safe work practices in handling HCN and cyanide salts, and on first-aid procedures in poisoning by these compounds.
(c) When HCN gas is used as a fumigant, warning signs shall be prominently displayed about the area and at all entries to the area as Temporary Antidote
If aerosolized salt has been inhaled or if solid or dissolved salt has caused poisoning after contact with the skin: Break an amyl nitrite ampule in a cloth and hold lightly under nose for 15 seconds. Repeat 5 times at about 15-second intervals. Repeat as necessary using a fresh amyl nitrite ampule every three minutes. Use artificial respiration if breathing stops.
If cyanide salt in any form is swallowed: proceed as above. If the victim is conscious and capable of some activity, give an emetic (1 tablespoonful of table salt in a glass of warm water) in repeated doses until the vomit fluid is clear. Never give anything by mouth to an unconscious person.
(e) Containers of Ca(CN)2 shall be labeled in the same manner as other solid cyanide salts, except that an additional warning is necessary because this material will react with water to release hydrogen cyanide.
The statement of the hazard shall read as follows for Ca(CN)2:

# DANGER! MAY BE FATAL IF SWALLOWED OR INHALED CONTACT WITH WATER OR ACID LIBERATES POISONOUS GAS CAUSES EYE BURNS AND MAY IRRITATE SKIN (f)
All containers of solutions of cyanide salts shall bear the following labeling in addition to, or in combination with, labels required by other statutes, regulations, or ordinances. The proper chemical name of the specific inorganic cyanide compound followed by the word "solution"
shall appear in large, bold face type at the top of the label.
(insert name of compound) SOLUTION (Inorganic Cyanide Solution) DANGER! MAY BE FATAL IF SWALLOWED OR ABSORBED THROUGH SKIN CAUSES BURNS CONTACT WITH ACID LIBERATES POISONOUS GAS Do not breathe gas. Do not get in eyes, on skin, on clothing. Wash thoroughly after handling. Keep container closed and away from acids. In case of contact, immediately flush skin or eyes with plenty of water for at least J.5 minutes and call a physician. Treat spillage with strong calcium hypochlorite solution and flush to sewer.

# POISON First Aid
Always have on hand a Cyanide First-Aid Kit. Carry patient to fresh air, have him lie down.
Remove contaminated clothing but keep patient warm. Start treatment immediately. Call a physician.

# Temporary Antidote
If gas is inhaled: Break an amyl nitrite ampule in a cloth and hold lightly under nose for 15 seconds. Repeat 5 times at about 15-second intervals. Repeat as necessary, using a fresh amyl nitrite ampule every three minutes. Use artificial respiration if breathing stops. If swallowed: Break an amyl nitrite ampule in a cloth and hold lightly under nose for 15 seconds. If patient is conscious, or when consciousness returns, give emetic (1 tablespoonful of salt in a glass of warm water) and repeat until vomit fluid is clear. Repeat inhalation of amyl nitrite ampule every three minutes. Use artificial respiration if breathing stops. Never give anything by mouth to an unconscious person. Engineering controls and safe work practices shall be used to maintain exposures to HCN and cyanide salts below the prescribed limits.
Administrative controls may also be used to reduce exposure. However, because the inhalation of cyanides or their absorption through the skin may be immediately dangerous to life, the added protection of personal protective equipment and clothing must be provided for work procedures and for emergency situations as discussed below. Such equipment and clothing must be provided to the workers engaged in work with cyanide. Emergency equipment shall be located at well marked and identified stations within the cyanide work areas. This equipment must allow each and every worker to escape the area in case of a cyanide emergency.

# (a) Respiratory Protection
Engineering controls shall be used whenever feasible to maintain airborne cyanide concentrations at or below the environmental limits recommended in Section 1 above. Compliance with the permissible exposure limits by the use of respirators is only allowed when airborne cyanide concentrations are in excess of the workplace environmental limits while required engineering controls are being installed or tested, when nonroutine maintenance or repair is being accomplished, or during emergencies. Appropriate respirators as described in Table 1-1 for HCN and Table 1-2 for cyanide salts shall be used only when permitted by the above restrictions. Respirators shall be selected and used in accordance with the following requirements:
(1) For the purpose of determining the type of respirator to be used, the employer shall measure, when possible, the airborne concentration of HCN or cyanide salt in the workplace initially and thereafter whenever process, worksite, climate, or control changes occur which are likely to increase the airborne concentration of these cyanides.
The employer shall ensure that no worker is being exposed to cyanide in excess of the standards either because of improper respirator selection, fit, use, or maintenance.
The employer shall provide respirators in accordance with Tables 1-1 and 1-2 and shall ensure that the employee uses the respirator provided.
(4) Respiratory protective devices shall be those approved under the provisions of 30 CFR 11, published in the Federal Register, March 25, 1972, as amended.
(5) Respirators specified for use in higher concentrations of HCN may be used in atmospheres of lower concentrations. Likewise, respirators specified for use in higher concentrations of cyanide salts are permitted in atmospheres of lower concentrations.
The employer shall ensure that the respirators are adequately cleaned, maintained, and stored when not in use, and that employees are instructed in the use of respirators assigned to them and in testing for facepiece leakage before each use.
Cartridges or canisters shall be discarded and replaced with fresh canisters after each use. Unused canisters shall be discarded and replaced when seals are broken, after three years if seals are unbroken, or on the manufacturer's recommendation, whichever is first.
Cartridges and canisters shall not be used for periods of time in excess of those indicated in Tables 1-1 and 1-2.
(8) Emergency and escape-type respirators shall be made immediately available at the work stations for each worker when there is potential for exposure to concentrations of the various cyanides above the ceiling values.
For purpose of selection of respiratory protective equipment, entry into areas containing unknown and/or suspected dangerous atmospheric concentrations of HCN or cyanide salts shall be treated as an emergency. Less than or equal to 90 ppm (1) Type C supplied-air respirator, demand or continuous-flow type (negative or positive pressure), with half or full facepiece.
(2) Full facepiece gas mask, chin-style canister specific for HCN. The maximum service life of canisters is one hour.
Less than or equal to 200 ppm Full facepiece gas mask, front-or backmounted type canister specific for hydrogen cyanide. The maximum service life of canisters is one hour.
(1) Self-contained breathing apparatus in pressure-demand mode (positive pressure) with full facepiece worn under gas-tight suit providing whole body protection.
(2) Combination supplied-air respirator, pressure-demand type (positive pressure), with auxiliary self-contained air supply and full facepiece; all worn under gas tight suit providing whole body protection.
(1) Positive pressure self-contained breathing apparatus worn under a gas-tight suit providing whole body protection.
(2) Combination supplied-air respirator, pressure-demand type, with auxiliary selfcontained air supply; all worn under gastight suit providing whole body protection.
(1) Self-contained breathing apparatus in demand or pressure-demand mode (negative or positive pressure).
(2) Gas mask, full facepiece or mouthpiece type, with canister specific for HCN.

# NOTE:
During the use of any respirator with half mask, full facepiece or hood, protective clothing should be worn if there is a chance that liquid HCN may contact any part of the body.
Greater than 200 ppm Emergency (no concentration limit)
Evacuation or Escape (no concentration limit) Less than or equal to (1) Filter type respirators, approved for 25 mg/cu m toxic dust, with half-mask (not appli cable for Ca(CN)2).
(2) Chemical cartridge respirators with replaceable cartridge for toxic dusts and acid gases; with half-mask. Maximum service life 4 hours.
(1) Full-face gas mask, chest or back mounted type, with industrial size canister for toxic dust and hydro cyanic acid gas. Maximum service life 2 hours.
(2) Type C supplied air-respirator, continuous-flow or pressure-demand type (positive pressure) with full facepiece.
(3) Type A supplied-air respirator, (hose mask with blower) with full facepiece.
Greater than 50 mg/cu m (1) Self-contained breathing apparatus with positive pressure in full facepiece.
(2) Combination supplied-air respirator pressure-demand type with auxiliary self-contained air supply.
(1) Self-contained breathing apparatus with positive pressure in facepiece.
(2) Combination supplied-air respirator, pressure-demand type, with auxiliary self-contained air supply.
Evacuation or Escape (no (1) Self-contained breathing apparatus in concentration limit) demand or pressure-demand mode (negative or positive pressure).
(2) Full-face gas mask, front or back mount type with industrial size canister for toxic dust and hydro cyanic acid gas.

# Emergency (no concentration limit)
Less than or equal to 50 mg/cu m (b)
Protective Clothing
Because HCN and cyanide salts, dry or in solution, may be absorbed readily through the skin or any break in the skin, the provision and use of protective clothing are necessary for the protection of workers in most operations where HCN and cyanide salts are used in pure or diluted condition.
(1) When entering a HCN gas-filled area in emergency situations, when the airborne concentration of HCN is unknown, or when the known airborne concentration is greater than 200 ppm, employees shall wear gas-tight suits in addition to the required respiratory protection. The gas-tight suits shall provide full body protection.
(2) Employees engaged in maintenance, repair, or other work on equipment, or in circumstances whereby they may be exposed to HCN liquid or gas, shall wear protective garments or suits made of material impervious to HCN and providing full body protection.
(3) Employees shall wear rubber gloves when engaged in any activity which may involve the handling of, or possible contact with, HCN.
Employees shall wear gloves when handling dry cyanide salts and when using or handling equipment whose surfaces may be contaminated with these salts in such manner that contact of the chemical with the employee's hands is possible or likely.
Employees shall wear gloves made of rubber or other impervious material when engaged in any operation wherein contact of the hands with solutions of cyanide salts is possible or likely.
Employees shall wear protective sleeves, aprons, and/or full body protective clothing as needed to protect their skin from contact with cyanide salts, dry or in solution. When handling solutions, the outer garment shall be of rubber or other material impervious to the solutions involved in the exposures. The garments shall fit snugly about the wrist, arm, neck, waist, and/or ankle (as appropriate to the particular garment) and shall have closures which will exclude dust, powder, mist, and/or splashes of cyanide salts in either dry or liquid formulations.
(10) In areas where spills or splashes of solutions of cyanide salts are likely to occur, the employees shall wear shoes, boots, or overshoes made of rubber or other material impervious to these solutions.
(11) Chemical safety goggles shall be worn by employees engaged in any operation wherein there is danger or likelihood that dusts or solutions of cyanide salts will come into contact with the eye.
Full-length face shields with forehead protection shall be worn by employees engaged in any operation wherein there is danger or likelihood that dusts, molten salts, or solutions of cyanide salts may contact the face.
The employer shall be responsible for maintaining all devices and clothing to be used for personal protection in a clean and effective condition. (2) Buildings in which HCN is to be stored, handled, or used must be designed to prevent fire and explosion hazards and to minimize the release of the highly toxic liquid or gas. Equipment and vessels containing or using HCN should be isolated in rooms or buildings designed for, and devoted to, these purposes.
Building construction shall be fire-and explosion-resistant and shall meet the requirements of the National Fire Protection Association codes and of the local codes, regulations, and ordinances. Explosion vents and fire doors shall be provided in accordance with codes and good practice.
Each room or building shall have no less than two means of exit, with doors opening outward and provided with "panic bar" release latches.
Exits shall be provided so that no location within the room or building is more than 75 feet from an exit and personnel can be evacuated in less than 1 minute.
(3) All regular work areas where HCN is handled or used must be adequately ventilated so that, under normal or reasonably anticipated operating conditions, the airborne concentrations of HCN will not exceed the standard recommended in Section 1.
Local exhaust ventilation shall be used at points or areas of regular or anticipated release of HCN gas.
Equipment for very high rates of ventilation of an area may be provided for the rapid reduction of contamination of air by HCN when emergency situations arise.
The HCN-contaminated air from an exhaust ventilation system must either be passed through a suitable collector to remove the HCN or be discharged at a location or in a manner such that persons or animals will not be endangered by the toxic gas.
Ventilation equipment must meet the applicable codes for explosionproof and fireproof installation of such equipment. where applicable, shall be followed.

# (b) Cyanide Salts
(1) All necessary precautions must be taken to prevent cyanide salts from coming into contact with liquid or airborne acids. In addition, precautions must be exercised to prevent Ca(CN)2 from coming into contact with water or humid atmospheres.
Cyanide salts must be protected also from contact with large concentrations of carbon dioxide. Carbon dioxide fire extinguishers must not be used where cyanide salts are present.
In any circumstance in which there is probable contact of cyanide salts with liquid or airborne acids such as Cr03, S02, C02, HC1 etc, or of Ca(CN)2 with a high concentration of water vapor or with liquid water, the standards and requirements applicable to exposures to HCN shall also apply.
( All containers of cyanide salts must be labeled in accordance
with the recommendations in Section 3.
Areas in which cyanides are stored must be posted in accordance with the recommendations in Section 3.
(3) When containers of cyanide salts are removed or unloaded from trucks, boxcars, or poorly ventilated spaces, these should be thoroughly ventilated, purged, and tested before a worker enters.
When cyanide salts are placed in other containers for transport or temporary storage, such containers must be properly covered and labeled.
(A) Mechanical exhaust ventilation by local exhaust shall be provided for all operations producing, or likely to produce, dust or mists of cyanide salts in excess of the limit recommended in Section 1, or to vaporize HCN in excess of the recommended limit for that vapor.
Examples of such operations are: there is evolution of mist from the bath, the employees shall be encouraged to wear at least a filter type respiratory protective device as a measure of protection in addition to that provided by ventilation.
Nonreturnable containers and other containers or equipment contaminated with cyanides before being discarded should be washed thoroughly with alkalinized water to remove cyanide residues.
(10) When cyanide salts are used in fused salt baths, mechanical local exhaust ventilation should be provided to control any cyanide emissions.
Care in operation of the bath and in housekeeping must be exercised so that the area around the bath does not become covered with cyanide-containing powder or dust. Employees working at baths of fused cyanide salts should wear face shields and appropriate protective clothing to protect them from burns and skin contact with cyanides in the event of splashes. A shovel or similar tool should be used to add cyanide salts to a fused salt bath. The cyanide salt should not be added directly by hand.
(11) Inspection, cleaning, or repairing of tanks or other equipment used with solutions of cyanide salts should be performed only by properly trained workmen under careful supervision.
(A) The tank should be drained of all cyanide solution as completely as possible, then filled with alkalinized water and allowed to stand for 15 minutes, preferably with agitation. This procedure should be repeated; then a preliminary inspection may be made. Any encrustation should be removed by mechanical means and/or by means of a stream of water from a hose.

# (B)
If the tank is to be entered, the atmosphere in the tank should be tested for the presence of hydrogen cyanide and cyanide salts, to be certain it does not contain a dangerous airborne concentration of these or other materials.
(C) The tank should be purged with fresh air to ensure an adequate oxygen supply and air should be supplied to the tank while the worker is in the tank.

# (D)
Equipment other than tanks should be washed and vented similarly, as applicable.
In the event of finding airborne concentrations of cyanide salts in excess of the limit, immediate action must be taken to eliminate the cause of the elevated airborne cyanide concentration. In case of any emergency situation (spills, leaks, or other unusual emissions of cyanide which result or potentially may result in dangerous airborn concentrations), all personnel shall be evacuated from the area. The personnel required to return to the area to institute corrective measures shall wear approved respiratory protective gear while entering and working in the area until the situation is corrected.
(13) Any area in which there is the potential of an emergency involving HCN or a cyanide salt shall be posted in accordance with the provisions of Section 3, and emergency equipment stations shall be established. These stations shall be sufficient in number and so located as to be readily and immediately accessible to the workers in the area.
The stations shall be provided with first-aid supplies and instructions for first-aid treatment of any persons suffering excessive exposure to cyanide.
Approved type respiratory protective devices, as indicated in Section 4, shall be available at designated emergency stations. These devices shall be sufficient in number for the workers in the area and readily accessible. Occurrence and Use HCN is a colorless gas  or a colorless or bluish-white liquid  with a faint, characteristic odor of bitter almonds  perceptible to some people.  Kirk and Stenhouse  reported that 88% of 244 persons tested could smell hydrogen cyanide but that in a fourth of these, the determination was made only with difficulty.
The glucoside amygdalin which occurs in nature in some plants, notably almonds,  readily yields HCN upon hydrolysis. Recently, attention has been brought to the presence of HCN in automobile emissions.  HCN is manufactured in the United States from coke-oven gas by reaction with sodium carbonate, from cyanide salts by reaction with acid, by the decomposition of formamide, from the reaction of ammonia, air, and natural gas, or, most commonly, from the reaction of methane and ammonia under specific controlled conditions.  The great bulk of the HCN synthesized is used directly in the same process system.  In 1973, the estimated consumption of HCN in the United States was approximately 310,000 short tons.  HCN is used primarily in the production of chemical intermediates for the manufacture of synthetic fibers,  plastics,  cyanide salts  and nitrites; in the fumigation of ships,   In the presence of any source of hydrogen ions in quantity, eg, strong mineral acid, the production of HCN from cyanide salts becomes both rapid and large. Above 50 degrees C, an irreversible decomposition to formate and ammonia, as shown below, becomes important.  In the presence of NaCl, the hydrolysis of NaCN to HCN is increased at temperatures below 80 C, but decomposition to ammonia and formate is retarded.  Sodium cyanide is marketed as a powder, granule, flake or block in pillow-shaped pieces weighing about 1 oz, and as a 30% aqueous solution.
 Solid sodium cyanide is packed in steel or fiber drums, and the aqueous solution is shipped in tanks by truck or rail.  Potassium cyanide, KCN, is a white crystalline, deliquescent, solid. KCN is produced by methods similar to those for NaCN.  The chemical reactivity of KCN is similar to that of NaCN.  Hydrolysis to HCN, as was the case with NaCN, is slight (Kh = 2.54 x 10 exp(-5)).  Potassium cyanide is sold in forms similar to those of NaCN but because KCN is more expensive, its world production for 1963 was only 5,000 tons.  Calcium cyanide, Ca(CN)2, is also called "black cyanide" and is the only commercially important alkaline earth cyanide.
 The hydrolysis of Ca(CN)2, which takes place in two steps, as shown below, is complete.
 The resulting calcium hydroxide has dissociation constants of 3.74 x 10 exp (-3) and 4.0 x 10 exp (-2) but is much less soluble in water at 0 degrees C than sodium hydroxide  so that its aqueous solutions are not as alkaline.
For example, the pH of an aqueous solution of Ca(0H)2 in an electric furnace above 1000 C in the presence of sodium chloride.
saturated
 Rapid cooling apparently prevents the reversion to calcium cyanamide.
 It is manufactured primarily in Canada, South Africa, and East Germany and sold as flakes or blocks.
There is also some production elsewhere in Europe and Japan.
 in 1898 to kill vermin in railway cars,  in to kill bed bugs in prisons,  and, after 1910, for the fumigation of the holds of ships.  Stock and Monier-Williams   Cytochrome c absorbs radiation at 550 nanometers (nm). In the presence of cytochrome oxidase, the optical density at 550 nm decreases at a rate directly proportional to the activity of cytochrome oxidase. This rate of change was determined in the presence of cyanide, demonstrating the ability of cyanide to inhibit cytochrome oxidase activity. Additions of methemoglobin, in which the iron had been oxidized electronically to the ferric state, to a solution containing cytochrome c, cytochrome oxidase, and cyanide were found to increase the activity of cytochrome oxidase, thus reversing the inhibitory effect of cyanide. The authors also found that the addition of cyanmethemoglobin to a solution of cytochrome c and cytochrome oxidase had no immediate effect on enzyme activity, but after a few minutes the enzyme became increasingly inhibited. Thus, the authors demonstrated in vitro the abilities of cytochrome oxidase and methemoglobin to compete in a reversible fashion for the cyanide ion.
In a 1958 survey, Dixon and Webb  found that the concentration of cyanide necessary for inhibition of cytochrome oxidase was 2-6 orders of magnitude less than those required for inhibition of other enzymes. The interference of CN with many different enzyme systems other than those involved in respiration may thus contribute to its toxicity.
Schubert and Brill  in 1968 measured the inhibition and recovery of liver cytochrome oxidase in mice, rats, and gerbils after the intraperitoneal administration of KCN. Inhibition of the enzyme was found to reach a maximum 5 to 10 minutes after the cyanide injection. Depending on the dose, the enzyme activity returned to normal 5 to 20 minutes after maximal inhibition in mice but required up to 1 hour or more in the rat and gerbil. Interestingly, they found that the abilities of mice and rats to tolerate divided doses of cyanide depended on the total dose as well as on the time-dependent degree of enzyme inhibition. For example, they found that mice invariably survived a single sublethal dose of 6 mg/kg of KCN but not two doses of 3 mg/kg given 6 minutes apart or three doses of 2 mg/kg given at 6 minute intervals. They further showed that sodium thiosulfate and nitrite were able to reactivate liver cytochrome oxidase within minutes when administered to cyanide-treated rats and mice. Both men complained of headache and weakness or fatigability and were observed to have slight lid lag, enlarged thyroids, and excessive perspiration. One of the two also experienced dizziness and mental confusion, slurring of speech, coughing, sneezing, and occasional abdominal cramps, nausea, vomiting, and coarse tremor of the extremities followed by their temporary paralysis. Both men were exposed to cyanide aerosols generated by case hardening. Some exposure to HCN may have occurred.
Wuthrich  in 1954 described a 39-year-old German blacksmith who was exposed to cyanide in case hardening on a sporadic basis for 2 years and then more frequently for the next 4 years. The worker noticed some initial irritation, followed by a general worsening of health. He experienced loss of appetite, nervousness, vertigo, headaches, nausea, and vomiting.
During 2-3 week vacations, the symptoms disappeared but reappeared within a month after returning to work. His thyroid gland was slightly enlarged. After exposure to cyanide had ceased for about 14 days, the man was given a placebo of NaCl, iv, for three days during which time he reported an improvement in his condition. On the 4th day, 1.4 g of sodium thiocyanate was substituted for NaCl in the daily injections. The thiocyanate concentration in the blood serum increased rapidly following these injections and did not decay to normal between injections. From the day of the first NaSCN injection, the man began to complain of nausea, lack of appetite and nervousness. After three NaSCN injections, he reported nausea and vomiting and spontaneously stated that he felt the same symptoms as at his workplace.
If there are 5200 ml of blood in the average man, then a dose of and eventually by complete disappearance of P waves. A secondary increase in rate, but not to the rate prior to administration of HCN, was observed during the 3rd and 4th minutes along with the irregular reappearance of P waves, some of which were not conducted. All subjects showed A-V dissociation with a secondary decrease in rate during the 5th minute.
During the 6th and 7th minutes, the heart rates again showed a slight increase and a return to normal sinus rhythm. Thereafter, the heart rates slowed progressively. Normal A-V conduction in one man and incomplete A-V block in another were maintained throughout the period of observation (approximately 13 minutes).
A third subject developed Wenckebach's phenomenon, (2:1 block), and, finally, complete heart block. The fourth subject's heart had normal A-V conduction until the 14th minute, when it developed ventricular tachycardia and ventricular fibrillation. It must be remembered that the concentrations of HCN to which these men were exposed were huge, so that the details of the changes in their ECG recordings may not be entirely typical of those to be expected in occupational exposures.
Wexler's observations do seem to demonstrate that cyanide has no specific action on the heart but rather exerts on the myocardium actions that are typical of hypoxia and anoxia.
There have been several reports of exposure to HCN which included both the airborne concentration of HCN and the human physiological response. However, in many cases no additional information relating to worker exposure was provided. These reports are summarized in Table XIV-5.
In many cases it is difficult to attribute a specific concentration range directly to a group of investigators since many of the citations involve reference to the work of others with no additional supporting information.
Therefore, the validities of concentrations presented only by secondary references may be questioned. In large part they appear to be based on the unreferenced work of Lehmann and Hess. However, the application of

# Lehmann's data to man has been questioned by McNamara  because
Lehmann's work was apparently done entirely with rabbits, which McNamara considers to be more sensitive to a given dose (product of concentration and time) of HCN than man. He concluded that man has a susceptibility to HCN more like those of the comparatively resistant goat and monkey and on
this assumption (and one that the LCt50 for man is four times that for the mouse) has estimated that 3,404 mg/cu m will cause 50% mortality in humans exposed to it for one minute. McNamara estimated that a concentration of HCN of 607 mg/cu m would kill 50% of men after a 10-minute exposure.
The various fatal doses of HCN seen in Table XIV had just returned from a 13-month leave of absence 5 months prior to this episode.
In use, the solution was heated to boiling whereupon 50 ml of hydrogen peroxide were added. The gold articles were cleaned in a manner causing splashing on the skin and the production of a visible aerosol.
There may have been some exposure to HCN. A study of plant records revealed another plater who developed typical signs and symptoms in 1 month. The man had been treated for 7 weeks, was removed from exposure, and recovered. An investigation of the plant was made and these 19 illnesses were attributed to aerosols emitted by the improperly operated plating tanks. After engineering controls and housekeeping procedures had been instituted, there were no recurrences of these illnesses. No airborne concentrations of contaminants were reported.
Elkins  in reported that in a plant where there was considerable brass plating the ambient air contained a mist. The mist was reported to have contained NaCN in a concentration not greatly exceeding 5 ppm, expressed as HCN. Severe irritation was a widespread complaint and there were some incidents of ulceration of the nasal septum. The author noted that other alkalies of undetermined concentration in the air may have contributed to the irritating action of the mist. with the exception of one with a perforated septum who gave a history suggestive of previous exposure to chromates. The cyanides were not described but they were likely a mixture of NaCN, KCN, and some alkaline complex of CuCN in the copper plating tanks, and alkaline NaCN in the zinc bath.
In None of the four unexposed men had evidence of disease of the stomach or duodenum. The author reported that three of the exposed and two of the unexposed men had erythrocyte counts above 5,000,000 but below 6,100,000/cu mm and that seven of the exposed and none of the unexposed men had a percentage of lymphocytes above 40 but below 49%. He attributed the latter change to stress resulting from repeated exposure to small doses of HCN. He concluded that his results demonstrated that not all the effects of repeated acute or subacute exposures to HCN are entirely reversible.
In  Exposure was continued until the animals became apneic, their heart beats became irregular and weak, and distinct cyanosis was apparent. Administration of oxygen through a plaster of Paris mask, modelled to fit the rabbit's muzzle, by hand pressure applied to a rubber bag connected to the mask succeeded in reviving 18 of the 36 rabbits. The authors stated that the hearts of the other 18 rabbits had become too weak when oxygen administration was started to be able to perform the necessary movement of oxygenated blood to the important organs.
In 1951, Moss et al  exposed 16 rats to HCN at 24-465 ppm for up at 22 minutes. The rats exposed at 25-50 ppm survived, except for one exposed at 50 ppm. This rat was violently agitated after 1 minute 49 seconds, paralyzed after 2 minutes 30 seconds, unconscious after 3 minutes, and dead after 8 minutes.
In experiments reported in 1952 by Haymaker et al,  six dogs were exposed at concentrations of 620, 590, 700, 700, 165, and 690 mg/cu m, for periods of 2.0, 2.0, 1.75, 1.75, 10.0, and 2.0 minutes, respectively.
The first three dogs died in 20 hours or less and the others were killed 24, 26, and 28 hours after exposure. Four of the six dogs had convulsive seizures. The dog exposed at 620 mg/cu m had marked proliferation of histiocytes in the leptomeninges and in the perivascular spaces of the molecular layer of the cerebellum. Only shadows of the Purkinje cells remained. Some of these dogs suffered necrosis of gray matter. Definite alterations of structure were not seen in dogs that died within 21 minutes after being exposed to HCN; they were found in dogs that died 2.5 or more hours after exposure. At these comparatively early times, there was subpial edema of the cerebrum and the cerebellum. Dogs that survived for as long as 16 hours had cellular damage, particularly in the cerebral cortex.
The frontal and parietal lobes were more likely to be affected than the temporal or occipital.
Cortical damage was concentrated frequently in the trough of a sulcus in the form of massive coagulation necrosis.
Valade  in 1952 exposed four dogs to HCN at 50 mg/cu m for 12 30-minute periods, conducted at 8-day intervals. Of these dogs, two survived, one died after 38 days, and one died of an intercurrent disease.
In a second experiment, four dogs were subjected to 19 30-minute inhalation periods at 2-day intervals and at the same HCN concentration. One died after 73 days, the other after 77 days. Another group of five dogs went through seven 30-minute inhalations at 2-day intervals, but this experiment was interrupted when pulmonary inflammation occurred, causing the death of three dogs. Still another group of four dogs were subjected to fourteen 30-minute inhalation periods at 2-day intervals; one of these died after 34 days.
The first signs were dyspnea, nausea, exaggerated intestinal peristalsis, and diarrhea. Later, the dogs developed tremors followed by loss of equilibrium and convulsions. These observations tend to support the hypothesis of a cumulative effect from exposure to HCN.
Valade  autopsied the dogs immediately after they died or were
killed and observed similar central nervous system lesions in each of them.
Vascular changes were vasodilatation and hemorrhages which were most pronounced in the central gray nuclei, brain stem, bulb, and medulla cervicalis.
Cellular lesions manifested themselves by glial reactions throughout the central nervous system and by cytologic changes in the Purkinje cells of the cerebellum and in the bulbar gray nuclei. These histopathologic examinations led the author to conclude that the lesions resulted from anoxia caused by inhibition of cytochrome oxidase or from a selective effect of the poison. To support the contention that the latter cause was the more significant, the author noted that the dogs were very quickly affected by respiratory disorders before the onset of other signs.
He thought there was reason to believe that the suddenness with which these disorders appeared was linked to a particular sensitivity of these animals' bulbar cells to cyanide, rather than to an inhibition of cytochrome oxidase. In 1955, Howard and Hanzal  reported a feeding study with HCNfumigated food. Thirty male and 30 female weanling albino rats were divided into 3 groups of 10 males and 10 females each. Two of the groups were given dog meal containing 300 ppm and 100 ppm of HCN, respectively. A third, similar group was fed unfumigated food as a control. At the end of a 2-year feeding period, no gross signs of cyanide toxicity were observed.
Autopsies revealed the same general abnormalities and signs of senility in control and experimental rats. Microscopic examination of heart, lungs, liver, spleen, stomach, small and large intestines, kidneys, adrenal, thyroid, testes or uterus and ovary, and the cerebrum and cerebellum revealed no evidence of pathology due to HCN feeding. All findings were compatible with those usually seen in aging animals, and the same general changes were found in both the control and the experimental animals.
Thiocyanate concentrations in plasmas, RBC's, and kidneys, but not in the livers, of rats given food containing 300 or 100 ppm HCN were about twice as high as those in controls.
In 1959, Levine and Stypulkowski  reported lesions in several areas of the brains of rats which survived exposure for 20-45 minutes at an unknown concentration of airborne HCN. The concentration of the airborne cyanide aerosol, which the authors presumed to be HCN, was not determined but was sufficient to debilitate the rats in 10 minutes. Earlier, Flury
and Zernik  found that persisting prostration occurred in 9.5 minutes at 127 ppm and, thus, it may be estimated that the rats in this experiment had exposures to HCN at approximately 127 ppm. Below this concentration (127 ppm), exposure to HCN for 2 hours did not produce brain lesions.
Above this concentration at which persisting prostration occurred, brain lesions were produced readily in 20-30 minutes. These lesions involved a multiplicity of sites in the brain although they were not universal in distribution.
For example, the cord, most of the stem, cerebellum, diencephalon, and portions of the cerebrum were spared. A predominance of isolated lesions appeared in the callosum and striatum. Later that same year, Levine and Weinstein,  using the same technique described above, reported that high concentrations of HCN generally caused the death of rats without causing brain damage. Low concentrations did not produce either, but moderate concentrations (perhaps 100-150 ppm) caused brain lesions while consciousness was maintained for an hour or so, followed by sudden unconsciousness and death. Unfortunately, in neither of these studies was the airborne concentration reported. Wistar albino rats receiving 0.5 mg of KCN subcutaneously once weekly for 22 weeks. They reported some pallid myelin but found it difficult to estimate whether or not there was demyelination. The animals appeared to be without other ill-effects from these small doses. The authors suggested that these lesions were due to excessive utilization of hydroxocobalamin to form cyanocobalamin. Whether these effects on nervous tissue are due to a specific action of the cyanide ion or of the thiocyanate ion, or to general histotoxic anoxia, is not clear.
Moss et al  in 1951 subjected from one to three rats to mixtures of CO and HCN. Atmospheres containing either HCN or CO alone were generally lethal to rats at concentrations of 50 or 5000 ppm, respectively.
A mixture of 10-20 ppm of HCN and 2000 ppm of CO was lethal to some.
Mixtures of 30 ppm of HCN and 1000 ppm of CO and of 5 ppm of HCN and 2000 ppm of CO were not lethal.
Hirner  in 1969 subjected male rats weighing about 250 g to subcutaneous injections of 0.2% KCN.
The daily dose, which averaged between 3 and 5 mg/rat, was divided into parts, which were injected within the span of 1 hour. Five rats received single daily doses and were killed 2 or 3 days later. Six rats received 4 to 12 daily doses, two received 14, and four received 20. All the multiply dosed rats were killed at the end of 9 weeks from the first daily dose. These rats were perfused through the left ventricle with a sodium cacodylate-glutaraldehyde solution;
appropriate samples of nervous tissue were ultrasectioned and examined electronmicroscopically as well as by conventional optical microscopy. The principal lesion found in this study was necrosis in the caudal part of the corpus callosum, with spongy alteration at the margin of the necrotic area.
Phagocytes invaded the necrotic area 2 days after the last dose of KCN; astrocytic gliosis followed. In the area of spongy change, there was vacuolization of axons and swelling of the astrocytes and oligodendroglia.
Demyelination was visible in the later stages of the study. Hirner considered that the effects on glial cells were primary effects of cyanide, but that disintegration of myelin and axonal degeneration were secondary effects, the axon remaining intact when swelling of the glia had occurred.
He stated the belief that the oligodendroglia are particularly susceptible to injury by cyanide. Unfortunately, neither report sought to quantify the dose of either HCN or KCN.
In the first study, Levine and Stypulkowski   In the second study, Levi and Amaducci  in 1968 brought their animals through the first two stages, after which they were allowed to partially recover, and were then killed by decapitation. The meninges appeared congested. Some rats had hemorrhagic pulmonary infarctions. In some animals trypan blue was injected iv to test the integrity of the blood-brain barrier. Subsequent examination of the brains did not show any abnormal passage of the trypan blue into the nervous tissue. Brain slices of other rats were used to study the active transport of amino acids.
Initial and steady state accumulation of amino acids and rates of amino acid exit were identical in brain slices from control and treated animals when a glucose-containing incubation medium was used. Tissue respiration rates were also measured in vitro and found to be identical in both control and treated animals. Thereafter, the analytical method selected determines cyanide radical content, and it is impossible to say what fraction of the total was attributable to any particular compound.
In order to differentiate between HCN gas and other cyanide compounds, it is necessary to first remove particulates by passing the air through an efficient filter, then absorb HCN from the stream by passage through an alkaline absorbing solution.
The filtered cyanides can subsequently be leached from the filter by treatment with alkaline solution, and the same analytical technique applied to both portions of the sample.
The presence of small quantities of cyanide in water was of concern long before relatively recent ecologic considerations led to an awareness that many other substances were toxic at trace concentrations. As a result, there exists substantial literature dealing with the qualitative and quantitative detection of cyanides in air and water, with at least one method (the titrimetric estimation of cyanide with silver nitrate published by Liebig  in 1851) still in use today, more than a century after its origination.  Almost all the methods proposed for the analysis of water or other materials have been, or can be, applied to the analysis of cyanides in air, for most air methods ultimately involve the determination of cyanide ion in solution. One of the most widely used colorimetric methods is the so-called pyridine-pyrazolone method, an example of the Konig synthesis for pyridine dyes, first published by Aldridge  in 1944 (using pyridine and benzidine) and subsequently modified by various authors.
 In this method, cyanides are converted to cyanogen bromide or cyanogen chloride, which then reacts with pyridine to form a glutaconic aldehyde.
Next, a primary aromatic amine reacts with the aldehyde to yield a colored Schiff's base. In the original procedure of Aldridge, the aromatic amine used was benzidine, but the more frequently used modification of Epstein  voltammetry , amperometry , coulometry  potentiometry  and others.  The most recently introduced and probably mosc useful in its application to air analysis, is the eleccrometric technique relying on specific ion electrodes, or ion selective electrodes which respond only to cyanide ion concentrations,  Cohen A -novel approach to determining cyanide levels has been described by OancniK and Br/lr.z  involving Indirect atomic absorption " spectrometric analysis.
In the first of two methods, the complex dicyano-bis-(l,10phenanthroline)-iron(II) is formed and then -.:tracted into chloroform. The
- iaiororG-ia is evaporated and the residue is taken ap m ethanol. The
- -.thaiioi. solution is aspirated directly into the flame, and iron equivalent 99 i to a known amount of cyanide is then determined. The second method is based on precipitating silver cyanide, then determining the excess silver ion in the supernatant by atomic absorption spectrometry.
In place of titrimetric techniques, several investigators have described methods in which turbidity resulting from the formation of silver cyanide, or the reduction in turbidity due to the formation of a cyanide complex with silver iodide, are measured.
, a specific ion electrode method , and a blood method using microdiffusion , first used by Conway.
 A respired air method based on the pyridine-pyrazolone reagent , as well as more general methods applicable to biologic samples using this same reagent are also used.
The rationale used in making a forensic diagnosis of cyanide poisoning have also received some attention.  Many of the methods listed have also been used for water and waste water analyses, and currently the methods most favored appear to be colorimetric, using some version of the pyridine-pyrazolone method, or modifications of the titrimetric determination with silver nitrate.
 Specific ion electrodes , and picric acid  have also been used.
Recently, an opto-acoustic infrared absorption technique as well as the titrimetric method utilizing silver nitrate have been used in the analysis of HCN in automobile exhaust.  Virtually every method used for cyanide analyses is subject to some interferences, usually due to the presence of certain metals which may form complexes, other anions, particularly sulfide, and a host of oxidizing and reducing agents. It is, therefore, frequently necessary to isolate the cyanide by some means, most frequently by a distillation from strongly acid solution, where all but the most tightly bound metal complexes are dis sociated to release hydrogen cyanide which is then absorbed in alkaline solution.
The recommended sampling and analytical method for the cyanides covered by this document is essentially that of the standard NIOSH method for cyanide in air as published in the NIOSH Manual of Analytical Methods.  should be followed.
High ventilation rate systems for the rapid dilution or removal of HCN gas and aerosols may be useful in some areas.
Control of the hazard of potential release of hydrogen cyanide from cyanide salts requires constant care and attention to good work practices.
The cyanide salts should be kept well apart from, and protected from contact with, acids, moisture, or elevated concentrations of carbon dioxide.

# Basis for Recommended Environmental Standard
Cyanide is well known as an acute, fast acting poison which can be described as insidious in that its toxic action at high concentrations is so rapid that its odor has no value as a warning.
 At lower concentrations the sense of smell may provide forewarning. For HCN, the primary routes of entry from occupational exposure are inhalation and absorption through the skin.
 Thus, it may be presumed by analogy that if 90 ppm of HCN is fatal, 96 mg/cu m of CN, derived from cyanide salts, may be also. Extending this analogy to threshold levels, presumably 11 mg/cu m of CN would be equivalent to the current Federal standard of 10 ppm of HCN and restriction of exposures to 11 mg/cu m of CN would protect against acute toxicity from cyanide salts.
However, taking into account the irritant effects observed from exposure to cyanide salts,  the current Federal standard of 5 mg/cu m of CN as an 8-hour time-weighted average appears to be too high in that it allows substantial excesses above that concentration for short periods of time.
Therefore, NIOSH recommends that the current value of 5 mg/cu m of CN be retained, but that its basis be changed from an 8-hour time-weighted average to a 10-minute ceiling. This action should provide the employee with adequate protection from the systemic effects of cyanide and prevent the erosional effects produced by the alkalinity associated with the cyanide salts.
A review of the cases involving exposure to cyanide reveals that they fall into three general categories. First are those cases in which there was an acute or subacute exposure followed immediately by an acute illness. [11,13,20,26,27 ppm. They also stated that it was difficult to give reliable limits for normal levels of cyanide and thiocyanate in the urine. However, in order to assess the hazards of occupational exposure, they considered it safe to state that nonsmokers who have greater than 400 #ig/100 ml of free thiocyanate in the urine, or smokers with urinary concentrations exceeding It is recognized that many workers are exposed to cyanides in concentrations considerably below the recommended occupational limits.
Under these conditions, it should not be necessary to comply with many of the provisions of the recommended standards. However, concern for worker health and well-being requires that protective measures be instituted below the enforceable limits to ensure that exposures do not exceed the standard.
Is given the super.vi sion necessary to assure that all safety tP'lii p r ;} r f \ c p c rn f-V. I (7) is instructed to shower before removing any respirator or gas-tight suit if prior contact with HCN liquid has occurred or is suspected;  (preferably sight contact) in a safe area or at a distance so as not to be affected by an emergency situation at the site of the first employee. The second employee ("buddy") should be alert and equipped to summon help and render aid, if needed.
The employee should carefully and precisely follow all operational procedures specified for the handling of HCN in containers, transfer operations, or other equipment. Suppliers' and manufacturers' instructions should be carefully followed.
When HCN is used for fumigation purposes, the space should be sealed to prevent the gas from leaking into surrounding spaces or areas. Warning signs should be posted and guards placed to keep unauthorized persons at a safe distance. All laws, regulations, ordinances, and codes applicable should be followed. Only licensed fumigators should do Such work.  Open containers of any solid cyanide salts or of solutions of cyanide salts should be limited to those necessary for operational requirements and procedures. Such open containers must be used only in adequately ventilated spaces so that the recommended standards for the airborne concentration of cyanide are not exceeded. Good practice dictates that, in so far as practical, covers be provided for such containers and used whenever possible.
Solutions of cyanides should be maintained as basic as practical to prevent any evolution of hydrogen cyanide. When weakly basic or neutral solutions are used, ventilation must be provided sufficient to prevent accumulation of the HCN evolved from exceeding the recommended standard for HCN in the work room air. When the addition of an acid to a cyanide solution may be necessary, the process should be fully enclosed and ventilated.
Respiratory protection should be provided for all workers potentially exposed to any release of hydrogen cyanide.
Fused salt baths containing cyanide salts should be provided with local exhaust ventilation. Care should be exercised in the operation of such baths to avoid spills and splashes. Addition of salts should be made carefully, using a shovel or special tool. The area about the bath should be regularly cleaned to prevent accumulation and encrustation of cyanide salts on adjacent areas. Workers at fused salt baths should wear safety goggles with side shields.
Local exhaust ventilation must be used for all operations emitting dusts or mists of cyanide salts.  Tanks and other equipment which must be entered for inspection, maintenance or repair, should be drained as completely as possible and then filled with water and agitated. After 15 minutes, they should be drained again and refilled for another 15 minutes, then drained again. The tanks should then be inspected for residue and encrustation of cyanides. These should be broken loose mechanically or by the force of a water stream and flushed away.
The tank should then be purged with fresh air, followed by testing for the absence of cyanide in the air before anyone enters. Cyanide waste solutions and cyanide-contaminated rinse or wash waters should be treated to destroy the cyanide before being discarded.
Treatment of cyanide waste is achieved by oxidation of the cyanide in alkaline solution by addition of chlorine or other oxidizing agents.

# IN AIR AND CALIBRATION
The same sampling and analytical methods are used for atmospheric hydrogen cyanide and the particulate cyanides. They can be collected and analyzed separately or by insertion of a filter can be simultaneously collected and individually analyzed. A sampling period of about 10 minutes is necessary to provide an amount of cyanide readily amenable to analysis by the cyanide selective electrode.

# Sampling
All glassware is washed in detergent solution, rinsed in tap water, and then rinsed with distilled or deionized water. Ten ml of an absorbing solution (0.1 M NaOH) is poured into an all-glass midget impinger using a graduated cylinder to measure the volume.
The fritted inlet of the impinger should have a porosity approximately equal to that of Corning EC (170-220 micron maximum pore diameter). A membrane prefilter (0.45 / u r n pore size) should be inserted (by means of an in-line cassette or similar device) before the impinger when sampling for particulate cyanides is to be performed.
Sampling for HCN and/or the particulate cyanides is performed for at least 10 minutes at a rate of 2 liters/minute, but the total volume of air sampled should not exceed 200 liters. A personal sampling pump or other satisfactory source of suction may be used for sampling provided it is calibrated as outlined below. Alternate sampling systems may be used, providing the required volume of air is sampled from the breathing zone of the worker.
Certain cyanide compounds, especially calcium cyanide, may hydrolyze at sufficiently high relative humidities, resulting in losses of collected sample as HCN gas. In such cases, it may be advisable to minimize losses by keeping the sampling time as short as possible, then storing it in a refrigerator until analysis.
It should be noted that when sampling for HCN without a prefilter, particulates will pass through the midget impinger. Likewise, when sampling for particulate cyanides by means of a midget impinger without a prefilter, HCN gas will also be collected and will constitute a positive interference.

# Calibration
Since the accuracy of an analysis can be no greater than the accuracy of measurement of the volume of air sampled, the accurate calibration of a sampling device is essential to the correct interpretation of an instrument's indication. The frequency of calibration is dependent upon the use, care, and handling to which the pump is subjected. Pumps should be calibrated if they have been subjected to misuse or if they have just been repaired or received from a manufacturer. If the pump receives hard usage, more frequent calibration may be necessary.
Ordinarily, pumps should be calibrated in the laboratory both before they are used in the field and after they have been used to collect a large number of field samples. The accuracy of calibration is dependent on the type of instrument used as a reference. The choice of calibration instrument will depend largely upon where the calibration is to be performed. For laboratory testing, a soapbubble flow meter or wet-test meter is recommended, although other standard calibrating instruments, such as a spirometer or dry-gas meter, can be used. The actual setup will be connected in sequence to the filter cassette or fritted impinger unit which will be followed by the sampler pump.
In this way, the calibration instrument will be at atmospheric pressure. If the personal sampler pump is used, each pump must be calibrated separately. If the buret is used, it should be set up so that the flow is toward the narrow end of the unit.
Care must be exercised in the assembly procedure to ensure that seals at the joints are airtight and that the length of connecting tubing is kept to a minimum. Calibration should be performed under the same conditions of pressure and temperature as those encountered in use. The calibrated pump rotameter should be used to set the flow rate in the field. Samples are analyzed using the cyanide ion selective electrode.

# Range and Sensitivity
The ultimate range and sensitivity of the method have not been established at this time. The recommended range of the method is 0.013-13 mg/cu m in air (approximately 0.0117-11.7 ppm of HCN).

# Interference
Sulfide ion irreversibly poisons the cyanide ion selective electrode and must be removed if found in the sample. Check for the presence of sulfide ion by touching a drop of sample to a piece of lead acetate paper.
The presence of sulfide is indicated by discoloration of the paper.
Sulfide is removed by the addition of a small amount (spatula tip) of powdered cadmium carbonate to the sample at pH 11-13. Swirl to disperse the solid, and recheck the liquid by again touching a drop to a piece of lead acetate paper. If sulfide ion has not been removed completely, add more cadmium carbonate. Avoid a large excess of cadmium carbonate and long contact time with the solution.

# METHOD FOR ANALYSIS OF CYANIDE SAMPLES
When a drop of liquid no longer discolors a strip of lead acetate paper, remove the solid by filtering the sample through a small plug of glass wool and proceed with the analysis.

# Precision and Accuracy
The precision and accuracy of this method have not been completely determined at this time. No collaborative tests have been performed on this method.

# Apparatus (a) Sampling and Calibration Equipment
(1) A filter unit (if needed) consisting of the filter media and cassette filter holder.
(2) A midget fritted impinger containing the absorbing solution or reagent.
(3) A pump suitable for delivering desired flow rates.
The sampling pump is protected from splashover or water condensation by an absorption tube loosely packed with a plug of glass wool and inserted between the exit arm of the impinger and the pump.
(A) An integrating volume meter such as a dry-gas or wet test meter.
(5) Thermometer ( 6) Manometer

# (f)
Precision and repeatability must be plus or minus 2% of full scale.
(g) It is desirable that the instrument respond only to HCN, but instruments which respond to other gases not normally present in the atmosphere may be acceptable.
In general, it is probable that any gas which causes a reading sufficiently high to set off the alarm will itself be present at a concentration sufficiently high to warrant corrective actions. Whenever there is a possibility that gases or vapors such as hydrogen chloride, chlorine, etc, may be present, it would be desirable to determine the response of the instrument to such gases in advance.
(h) An operating range of 0-100 ppm HCN is optimal, but other ranges may be selected to suit individual needs.
(i) The device should be capable of 7 days of continuous unattended operation.

# (j)
The device and alarm should be intrinsically safe for use in hazardous locations.

# Discussion
The principal requirements for such monitors in addition to responding to HCN gas are that they be sufficiently rugged to withstand normal extremes of temperature, pressure, vibration, etc, and not be susceptible to plugging or interferences due to contaminants likely to be encountered in most work places. They should be so constructed that it is possible to quickly check the zero setting of the instrument and the response at 25 ppm in a rapid routine manner. Chemical substances should be listed according to their complete name derived from a recognized system of nomenclature. Where possible, avoid using common names and general class names such as "aromatic amine,"
"safety solvent," or "aliphatic hydrocarbon" when the specific name is known.
The "%" may be the approximate percentage by weight or volume (indicate basis) which each hazardous ingredient of the mixture bears to the whole mixture. This may be indicated as a range or maximum amount, ie, "10-40% vol" or "10% max wt" to avoid disclosure of trade secrets.

# IX S P E C IA L PREC A U TIO N S P R E C A U T I O N A R Y S T A T E M E N T S O T H E R H A N D L I N G A N O S T O R A G E R E Q U I R E M E N T S P R E P A R E D B Y A O O R E S S O A T E

# XIII. APPENDIX V
First Aid and Treatment Kits Two physician's treatment kits should be immediately available to trained medical personnel at each plant where there is a potential for the release of, accidental or otherwise, or for contact with, hydrogen cyanide or cyanide salts. One kit should be portable in order that it may be carried by medical personnel while accompanying a patient to the hospital.
The other kit should be kept under lock and key to assure that it is intact and available when and if needed. The key should be readily available at all times to the work supervisor on duty and the storage place should be of such construction as to allow accessibility in the event of loss of the key.
Both kits for use by the medical personnel servicing each firm should contain the following as a minimum.
(1) Two (2) boxes (2 dozen) ampules; each ampule containing 0.3 ml of amyl nitrite.
(2) Two (2) ampules of sterile sodium nitrite solution (10 ml of a 3% solution in each).
(3) Two (2) ampules of sterile sodium thiosulfate solution (50 ml of a 25% solution in each).
(4) 2 sterile 10-ml syringe with intravenous needles.
(5) 1 sterile 50-ml syringe with intravenous needle.
(6) 1 tourniquet (7) 1 gastric tube (rubber).
(8) 1 non-sterile 100 ml syringe.
The medical personnel servicing a firm where there is a potential for hydrogen cyanide release or a potential for exposure to inorganic cyanide should be familiarized with the use of these kits.
First-aid kits should be immediately available at work places where there is a potential for the release, accidental or otherwise, of hydrogen cyanide or a potential for exposure to inorganic cyanide. This kit should contain as a minimum two (2) boxes of ampules ( 2 dozen), each containing 0.3 ml of amyl nitrite. Ampules should be replaced biannually or sooner if needed to ensure their potency.
The amyl nitrite ampules should be protected from high temperatures. In all cases, the contents of the medical and first-aid kits should be replaced before the manufacturer's assigned expiration dates.
First-Aid Procedure Speed in the rendering of first-aid treatment is of the utmost importance. The patient should be removed at once to an area free from HCN. The rescuer should wear respiratory protective equipment in order not to be overcome or weakened by the gas.
Many victims will have stopped breathing.
In this case, it is imperative that efforts at resuscitation be instituted at once and continued without interruption even while other treatment is being administered.
A physician should be summoned immediately.
First-aid kits should be readily available at all times. They should be quickly accessible but should not be kept only in operating areas mixtures with air may be explosive if a source of ignition is present.

# (B) Resuscitation
Before instituting artificial resuscitation, dentures and foreign objects, such as gum and tobacco, and any accumulated oropharyngeal fluids (saliva, etc) should be removed from the patient's mouth and pharynx and the tongue pulled forward.
If the patient's breathing is weak or has stopped, artificial resuscitation should be started at the earliest possible moment and continued without interruption until normal breathing has been established or the patient is pronounced dead.
Mouth-to-mouth resuscitation is the method of choice because of its simplicity and effectiveness. It is, however, impossible to administer amyl nitrite while using this method. Therefore, it is advisable to switch to other methods of artificial respiration, such as the Holger-Nielsen arm-lift back pressure method, during the periods when the amyl nitrite is being given.
If a mechanical resuscitator and personnel skilled in its use are available, this equipment may be used instead of other forms of resuscitation.
(C) The patient should be kept comfortably warm but not hot. Other drugs and stimulants are rarely necessary and should be administered only by a physician or trained medical personnel under the direction of a physician.    Step -Through the formation of a relatively stable coordination complex with ferric iron, cyanide tends to keep this metal in its higher oxidation state and thus reduces its efficacy as an electron carrier in ferric to ferrous iron transitions.
By such a complexation of iron, the respiratory enzyme ferricytochrome oxidase is changed to ferricytochrome oxidasecyanide and its ability to catalyze the reaction of reduced cytochrome with oxygen is inhibited, with consequent impairment of cellular oxygen utilization
Step -Since numerous metabolic pathways converge at the cytochrome system, the impairment of the cells' ability to utilize oxygen reduces or even stops aerobic metabolism. True histotoxic (cytotoxic) hypoxia results with a shift to anaerobic metabolism with accumulation of lactate, pyruvate, and glucose.
Step -The cells are thus unable to use the oxygen brought to them as 02Hb by the arterial blood. The oxyhemoglobin continues into the veins, the arteriovenous oxygen difference diminishes, and the venous blood is almost as bright a red as the arterial blood.
Step 4 -The chemoreceptors in the carotid and aortic bodies, which are the tissues most sensitive to cellular hypoxia, trigger an inspiratory gasp and hyperpnea as an almost instantaneous path ophysiologic effect of cyanide absorption.
Current concepts about the treatment of selected poisonings-nitrite, cyanide, sulfide, barium, and quinidine. Ann Rev Pharmacol Toxicol 16:189 -199, 1976 109.
Carmelo, S:  Rass Med Ind 24: 254-71, 1955 (Ita) 110.
El Ghawabi SH, Gaafar MA, El-Saharti AA, Ahmed SH, Malash KK, Fanes R: Chronic cyanide exposure: a clinical, radioisotope, and laboratory study. Br J Ind Med 32: 1975 111.
Wollman SH: Nature of the inhibition by thiocyanate of the iodide concentrating mechanism of the thyroid gland. Amer J Physiol 186: 1956 112.
Heymans JF, Masoin P:
 Arch Int Pharmacodyn Ther 7:297-306, 1900 (Fre) After sampling, the fritted impinger stem can be removed and cleaned in the following manner. Tap the stem gently against the inside wall of the impinger bottle to recover as much of the sampling solution as possible. Wash the stem with a small amount (1-2 ml) of unused absorbing solution and add the wash to the impinger bottle. Then the impinger bottle is sealed with a hard, non-reactive stopper (preferably Teflon) and an appropriate identifying number attached to it. Do not seal with rubber.
The stoppers on the impinger bottle should be tightly sealed to prevent leakage during shipping. If it is preferred to ship the fritted impingers with the stems in, the outlets of the stem should be sealed with Parafilm or other nonrubber covers, and the ground glass joints should be sealed, ie, taped to secure the top tightly. Upon completion of sampling for the particulate cyanides, plastic caps should be replaced on the inlet and outlet tubes of the cassette and an appropriate identifying number attached to it.
Care should be taken to minimize spillage or loss by evaporation at all times. Refrigerate samples if analysis cannot be done within a day. Whenever possible, hand delivery of the samples is recommended. Otherwise, special impinger shipping cases should be used to ship the samples.
A "blank" fritted impinger should be handled as the other samples (fill, seal, and transport) except that no air is sampled through this fritted impinger.
Where a prefilter has been used for the collection of particulate cyanides, the filter cassettes are capped and placed in an appropriate cassette shipping container. One filter disc should be handled like the other samples (seal and transport) except that no air is sampled through it, and this is labeled as a blank.

# M A TERIA L SAFETY DATA SHEET 1 PRO D U CT IDENTIFICATIO N M A N U F A C T U R E R 'S N A M E R E G U L A R T E L E P H O N E N O . E M E R G E N C Y T E L E P H O N E N O A D O R E S S

# TRADE N AM E S Y N O N Y M S II H A ZA R D O U S IN G R E D IE N T S M A T E R I A L O R C O M P O N E N T % H A Z A R D D A T A

# III P H Y SIC A L DATA

# O L E V A P O R A T I O N R A T E ( B U T Y L A C E T A T E M ) A P P E A R A N C E A N O O D O R
where they may not be available in case of a spill.
( (3) Inhalation (A) Administer amyl nitrite A pearl (ampule), if not provided with a fabric sleeve, should be wrapped lightly in a handkerchief or gauze pad, broken, and held about 1 inch from the patient's mouth and nostrils for 15 seconds.
Repeat 5 times at 15-second intervals. Use a fresh pearl every 5 minutes until 3 or 4 pearls have been administered.

# WARNING:
First-aiders should keep the pearls away from their own mouths and noses lest they become weak and dizzy and unable to give proper assistance to the victim. Amyl nitrite is flammable and