Asphyxiants

Define asphyxiant

A substance that impairs the ability of the body to absorb or utilise oxygen resulting in suffocation.

Impaired oxygen deliver to cells reults in cellular hypoxia and impaired ATP production. If prolonged can reult in cell death

Simple asphyxiant

Causes hypoxia by displacing oxygen and lowering the partial pressure of oxygen. FI02 is low and cannot saturate Hb. PHYSIOLOGICALLY INERT

Chemical Asphyxiant

causes hypoxia by interfering with cellular respiration.

Affects mitochondrial function and haemoglobin binding

Carbon Monoxide

Chemical Asphyxiant

Binds 240 x more strongly to Hb than Oxygen

Hydrogen Cyanide

Binds mitochondrial enzyme cytochrome a3 and blocks ATP production(Oxidative phosphorylation)/ electron transport chain, anaerobic metabolism and lactic acidosis

Cellular respiration affected

Hydrogen Sulphide

inhibits cytochome oxidase enzymes in mitochondria resulting in anaerobic respiration

inhibits cellular respiration

carbon monoxide

Reducing oxygen carrying capacity by binding to HB strongly. 240 times greater than 02

Binds to myoglobin reducing cardiac output

Binds to cytochrome oxidase

Ventilation during increased physical activity increases co binding

E.g 6% for sedentary, 8% for active at the OEL OF 8PPM

Half life of CO

ROOM AIR - 4 HOURS

100% 02 facemask- 60 to 90 min

Ventilation 60min

HYPERBARIC - 20 MIN

Rotten egg odour

low concentrations of Hydrogen Sulphide

Olfactory nerve paralysis at high levels of exposure

Bitter almond odour

Hydrogen cyanide

Also olfactory paralysis at high concentrations

CO FORMATION

INCOMPLETE COMBUSTION OF CARBON CONTAINING FUELS

COLOURLESS AND ODOURLESS

TREATED WITH 100% O2 FOR 6 HOURS

Increased exertion, heat, dehydrated and confined spaces worsen risk

CARBOXYHAEMOGLOBIN INTERPRETATION

A COHb concentration of more than 2% in a nonsmoker and >10% in a smoker confirms exposure to CO

1% NON SMOKER

4 to 7% typical SMOKER

Upto 10% not unusual

Headache at more than 10%

Collapse at more than 35%

IMPORTANT CONSIDERATIONS

CONFINED SPACE

SOURCE OF GAS

DOSE/CONCENTRATION , DURATION/TIME

COHB CONCENTRATIONS

SYMPTOMS ( RESP AND CNS START > 10%)

APPROACH 60% - SYNCOPE AND SEIZURES

APPROACH 80% - DEATH

Hydrogen Cyanide

Liquid at 26 celcius, heat vaporizes

Inhalation and absorption through skin

Stel is 10 ppm over 15 min. Death around 90 in 30min

Cellular respiration, cytochrome enzymes causing cellular hypoxia

Gold mining, electroplating

Skin ulcers at cuts

Formed when a cyanide containing compound reacts with acid

Nitrile group of compounds have cyanide groups e.g acrylonitrile and acetonitrile. Burning warehouse

20 to 40 % of people cannot smell the sweet almond smell

Rx with nitrites and oxygen

Inhalation of amyl nitrite or IV sodium nitrite

Iv Thiosulfate makes cyanide non toxic into a thiocyanide

Nitrites induce methemoglobinemia, feric ion competes with cyanide

Cobalt EDTA and hydroxocobalamin are safer than nitrites

Hydrogen sulphide sources

Lead sulphide mining - stinkdamp

Leather tanning uses sulphides

Manure and sewage

GATHER NEAR THE GROUND

C02, ETHANE

PREVENTION

OXYGEN CONCENTRATION DETECTION DEVICES TO CHECK AREA , AND IDENTIFYING AT RISK AREAS

SAFETY HARNASSES FOR WORKERS

SELF CONTAINED BREATHING APPARATUS

EMERGENCY OXYGEN ON HAND

OHSA DEFINITION OF OXYGEN DEFICIENT ENVIRONEMENT

<19.5%

ASYMPTOMATIC TO SOME SYMPTOMS AFFECTING THE CNS AND RESPIRATORY SYSTEM BETWEEN 16.519.5

EARLIEST SYMPTOM AT LESS THAN 16% - TACHYPNEA AND TACHYCARDIA AND INCOORDINATION

EMOTIONAL CHANGES< 14% AND EXHAUSTION

NAUSEA AND VOMITIND < 10%

NB: DEATH BELOW 6%

Hydrogen sulfide

Lead sulphide mining,iron pyrite decomposition in coal mines, hair removal from leather tanning

Rotten egg smell

Oel is 10 ppm, evacuation at 70ppm

Olfactory fatigue at 100ppm - false sense of security

Continuous air monitoring with alarm, oxygen, cyanide antdote kit and harness plus self containing breathing apparatus

Heavier than air. Sinks.

Nitrites antidote convert hb to methemoglobin and sulf hemoglobin forms. Must give o2

Coins and jewellery darken

List 3 simple asphyxiants and an industry/application

1. Nitrogen - ammonia production

2. Methane - Mining “black damp”

3. C02 - Fire extinguishers, mananufacture of lime, Firefighters

4. Argon- welding

5. Helium

NITROGEN

Colourless, odourless + poor venitlation spaces!!! dangerous esp if leaking cylinders

METHANE IS LIGHTER THAN AIR AND BELONGS TO THE ALIPHATIC HYDROCARBON GROUP

“FIRE DAMP”, FLAMMABLE - MINES

SEWAGE AND DECAYING MATTER, SEWERS, MANURE

NATURAL GAS

BIOLOGICALLY INERT, CAN CAUSE FROST BITE

COLLAPSE MAY BE THERAPEITIC

SIMPLE ASPHYCIANT THAT IS HEAVIER THAN AIR AND A RESPIRATORY IRRITANT THAT IS USED IN NATURAL GAS AS A FUEL

ETHANE

C02

SOUR TASTE, COLOURLESS AND ODOURLESS

OEL FOR CO2 5000 PPM OVER 8 HOURS I.E 0.5% PER VOLUME OF AIR

7-10% COS PER VOLUME OF AIR UNCONCIOUSMESS

SOURCES OF CO2

LIME MANUFACTURING

FIRE EXTINGUISHERS

CO2 WELDING

LEATHER INDUSTRY

SOLID”DRY ICE:” OR LIQUID OR GAS FORM

CAN BE CAUSE OF DEATH IN METHANE EXPLOSIONS - LAKE NYOS DISASTER

SCBA NECESSARY + HARBNESS AND CONTINUOS AIR MONITORING

FACTORS THAT INFLUENCE O2 DELIVERY AT A CELLULAR LEVEL

CARDIAC OUTPUT

O2 CONTENT OF ARTERIAL BLOOD