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: mechanism

Displaces oxygen

lowering the partial pressure of oxygen.

FI02 is low and cannot saturate Hb.

PHYSIOLOGICALLY INERT

Chemical Asphyxiant: mechanism

causes hypoxia by interfering with cellular respiration.

Affects mitochondrial function(cytochrome, enzymes)and haemoglobin binding

Carbon Monoxide

1. Type of asphyxiant

2. Binding strength

Chemical Asphyxiant

Binds 240 x more strongly to Hb than Oxygen

Hydrogen Cyanide:mechanism

Chemical asphyxiant

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

Cellular respiration affected

Hydrogen Sulphide: mechanism

inhibits cytochome oxidase enzymes in mitochondria resulting in anaerobic respiration

inhibits cellular respiration

carbon monoxide: mechanism

Aggrevating factors

Binds to HB strongly reducing oxygen carrying capacity.

240 times greater than 02

Binds to myoglobin reducing cardiac output

Binds to cytochrome oxidase

Ventilation during increased physical activity increases co binding

Confined spaces

E.g 6% for sedentary, 8% for active

OEL IS 50 PPM

Half life of CO

1. Room air

2. 100% 02 face mask

3. Ventilation

4. Hyperbaric

ROOM AIR - 4 HOURS

100% 02 facemask- 60 to 90 min

Ventilation 60min

HYPERBARIC - 20 MIN

Rotten egg odour

1. Which gas

2. Is it reliable?

low concentrations of Hydrogen Sulphide

Olfactory nerve paralysis at high levels of exposure

Bitter almond odour

1. Which gas?

2. Is it reliable?

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 via non rebreather face mask

Increased exertion, heat, dehydrated and confined spaces worsen risk

CARBOXYHAEMOGLOBIN INTERPRETATION

1. BEI

2. Typical range for non smoker

3. Typical range for smoker

4. 1st symptom above 10%

5. % for collapse

BEI 3.5 CARBOXYHB IN BLOOD

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 for Exposure assessment

CONFINED SPACE

SOURCE OF GAS

DOSE/CONCENTRATION , DURATION/TIME

COHB CONCENTRATIONS for symptoms

SYMPTOMS ( RESP AND CNS START > 10%)

APPROACH 60% - SYNCOPE AND SEIZURES

APPROACH 80% - DEATH

Hydrogen Cyanide

1. Form at room T

2. Two sources incl burning of acrylonitrile

3. Smell and %

4. Three treatments and mechanism of action

Liquid at 26 celcius, heat vaporizes

Inhalation and absorption through skin

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

Cellular respiration, cytochrome enzymes causing cellular hypoxia and cyanohb

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 immediate on the spot

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

1. Stink two sources

Lead sulphide mining and Coal mining from the decomposition of iron pyrite - stinkdamp

ACCUMULATES IN LOW AREAS BECAUSE HEAVIER THAN AIR

Leather tanning uses sulphides to remove hair from Hyde

Manure and sewage

SULPHIDES IS A SOURCE E.G. USED IN LEATHER TANNING AND EVEN CARBON DISULFIDE

GATHER NEAR THE GROUND

Two simple asphyxiant gases

C02, ETHANE

Practical measures and equipment for preventing incidents

List 4

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

1. Are most asymptomatic between 16.5 and 19

2. Earliest signs below 16.5

3. Two other important symptoms

4. Death at what %

<19.5%

ASYMPTOMATIC TO SOME SYMPTOMS AFFECTING THE CNS AND RESPIRATORY SYSTEM BETWEEN 16.5-19.5

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

1. Stink sources

2. Is smell reliable? Why not?

3. Where does it collect

4. Practical safety measures

5. Treatment including antidote

6. What happens to coins

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 simultaneously

Coins and jewellery darken

Acute effects: eye e.g. photophobia

Delayed are pulm oedema. Also look for haemaueia,lfts, sore throat and secretions

Not teratogenic or carcinogenic

Long term CNS effects e.g. facial nerve, or epse and cognitive and eye keratitis, conjunctivitis

List 3 simple asphyxiants and an industry/application

1. Nitrogen - ammonia production, coal mining “black damp”

2. Methane - Mining “fire damp”

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

4. Argon- welding

5. Helium

NITROGEN

1. Properties

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

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

1. Two sources

2. Physical hazard

“FIRE DAMP”, FLAMMABLE - MINES

SEWAGE AND DECAYING MATTER, SEWERS, MANURE

NATURAL GAS

BIOLOGICALLY INERT, CAN CAUSE FROST BITE

COLLAPSE MAY BE THERAPEITIC

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

ETHANE

C02

Properties

OEL

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

3 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