Active Asphyxiants

Ionised cyanide has a high affinity for ferric iron (Fe ) and binds with ferric iron in cytochrome oxidase of the electron transport chain within mitochondria. Free cyanide binds to cytochrome oxidase in mitochondria, interrupting the electron transport chain and decreasing the production of ATP. Anaerobic metabolism, therefore, takes over with the production of lactic acidosis. The actions of cyanide at the mitochondria have a very short latency period. 

Normally, there are low levels of cyanide in the body as a result of certain food products and inhalation contamination such as smoking. Small amount of cyanide is normally eliminated using an enzyme, rhodanese found in the liver. Rhodanese catalyses the reaction of cyanide (CN) with thiosulphate to produce thiocyanate (SCN) that is excreted later in the urine. This pathway is one of the means of treating cyanide poisoning as explained in the next chapter. 

---

The typical test (illustrated in Figure 15.7) is performed using mice, normally female CBA mice 6-10 weeks of age. Female BALB/c and ICR mice have also been used. After animal receipt, they are typically acclimated to standard laboratory husbandry conditions for 7-10 days. The usual protocol will consist of at least two groups (vehicle control and test article treated) of five mice each. They are treated on the dorsal surface of both ears with 25 pi (on each ear) of test article solution for three consecutive days. Twenty-four to forty-eight hours after the last test article exposure, the animals are given a bolus (0.25 ml) dose of [3H]thymidine (20 pCi with a specific activity of 5.0-7.0 Ci/mmol) in phosphate buffered saline via a tail vein. Five hours after the injection, the animals are euthanized by C02 asphyxiation and the auricular lymph nodes removed. 

Klop acquinite PS NC, Larvacide 100 Pic-fume. Russians used it in hand grenades in 1916 dissolved the chloropicrin in sulphuryl chloride (50%). Insecticide, fungicide, used to kill rats in ships. Oily liquid, yellowish in impure form, intense odour bp 112°C, attacks lead energetically, attacks iron and copper more slowly. Absorbed well by activated charcoal. Strong irritant and toxic asphyxiant. 

The function of acetylcholinesterase (AChE) is to degrade the neurotransmitter acetylcholine (ACh). "niere is general agreement that the acute toxicity of OP is explained by irreversible inhibition of AChE activity at cholinergic synapses (Chambers and Levi, 1992 McDonough and Shih, 1997 Mileson etal., 1998 Pope, 1999 Taylor, 2001 Casida and Quistad, 2004). Inhibition of AChE (>70%) leads to accumulation of ACh at central and peripheral sites. In the brain, overstimulation of ACh receptors can lead to seizures. Inhibition of the breathing center in the brain results in asphyxiation. In the diaphragm muscle, overstimulation of... 

Krypton, Kr, is an elemental, colorless, odorless, inert gas. It is noncombustible, nontoxic, and nonreactive however, it is an asphyxiant gas and will displace oxygen in the air. Krypton 85 is radioactive and has a half-life of 10.3 years. The four-digit UN identification number for krypton is 1056 as a compressed gas and 1970 as a cryogenic liquid. These forms of krypton are not radioactive. Radioactive isotopes of krypton are shipped under radioactive labels and placards as required. Its primary uses are in the activation of phosphors for self-luminous markers, detecting leaks, and in medicine to trace blood flow. 

Activity C-T. 1 is probably the most effective peripheral muscle relaxant. It is hardly used in current therapy because the corresponding diallylnortoxiferinium chloride (alcuronium chloride, Alloferin ) has a shorter duration of action. The muscle relaxant effect results from a (competitive) expulsion of acetylcholine from the receptors of the motoric endplates with paralysis of the transversely striated musculature (overdoses cause death by asphyxiation). 

In areas where fire potential and the risk of injury or damage are high, automatic fire-extinguishing systems are often used. These may be of the water sprinkler, foam, carbon dioxide, halon, or dry chemical type. If an automatic fire-extinguishing system is in place, laboratory workers should be informed of its presence and advised of any safety precautions required in connection with its use (e.g., evacuation before a carbon dioxide total-flood system is activated, to avoid asphyxiation). 

Many workplaces contain spaces that are considered confined because their configurations hinder the activities of employees who must enter, work in, and exit them. For example, employees who work in process vessels generally must squeeze in and out through narrow openings and perform their tasks while cramped or contorted. OSHA uses the term confined space to describe such spaces. In addition, there are many instances where employees who work in confined spaces face increased risk of exposure to serious hazards. In some cases, confinement itself poses an entrapment hazard. In other cases, confined space work keeps employees closer to hazards, such as asphyxiating atmospheres or the moving parts of machinery. OSHA uses the term permit-required confined space or permit space) to describe those spaces that both have confined space and have elements that pose health or safety hazards (see Rgure 25.4). 

Chemical Asphyxiants. These prevent either oxygen transport in blood or normal oxygenation of the tissues. Chemical asphyxiants are active far below the level required for damage from simple asphyxiants. Examples include carbon monoxide, hydrogen cyanide, and nitrobenzene. 

---