Module 3: Toxicology - Section 10:   Toxic Gases
TOX 10.3: Specific Toxic Gases

SPECIFIC TOXIC GASES:

I. Physical asphyxiants:

See: La Dou

II. Chemical asphyxiants:

1. Carbon monoxide (CO):
Source: Clinical:
Acute effects: Chronic effects: Ix: Carboxyhaemoglobin. Note: PO2 may be normal.
Rx: 100% 02. Observe.
Control: As per source. R-OEL: 50 ppm, (STEL 300 ppm)

Note: You are not expected to remember any specific numbers. However you do need to know where to look it up.

Question: What is a Recommended Occupational Exposure Limit (R-OEL)?
What is a Short Term Exposure Limit (STEL)? Clue: Revise the relevant section of the Hazardous Chemical Substance Regulations.
Hydrogen cyanide (HCN, prussic acid):

Source:

Clinical:
Acute: (a) Mucous membrane skin irritation (b) Hypoxia due to binding of cytochrome oxidase in cells. Bitter taste, headache, nausea and vomiting, dyspnoea, agitation, respiratory arrest.

Post-acute: Delayed CNS damage

Chronic: Persistent symptoms, neurologic deficit, goitre

Ix: Suspicion, blood thiocyanate
Rx: 100% 02, Amyl nitrite / Na nitrite IV, followed by Na thiosulphate IV
Control: Engineering, PPE, decontamination/evac. procedures. C-OEL: STEL (only) 10 ppm

Note: Hydrogen cyanide has a Control - OEL (C-OEL). Revise this concept.

3. Hydrogen sulphide (H2S):

Source:

Clinical:
Acute: Irritant (eyes, URT) plus cellular asphyxiant.
Post acute: CNS deficits
Chronic: ?

Diagnosis: History

Rx: 100% 02, Na nitrite (as an antidote).

Control:

III. Irritant gases:

Sulphur dioxide (SO2):
Source: Clinical:
Acute: Post acute: Reactive Airways Dysfunction Syndrome (RADS)
Chronic: Chronic bronchitis/COPD?

Ix: Airways function

Rx: Bronchodilators, systemic steroids

Control: As for source. R-OEL: 2 ppm (STEL 5 ppm)
Oxides of nitrogen (NO, NO2):
Source: Clinical
Acute: Relatively little impact on URT (low solubility) LRT damage! Delayed up to 24 hrs - bronchiolitis, alveolitis, pulmonary oedema.
Post acute: Obliterative bronchiolitis (Medics: look this up).
Chronic: ?Emphysema

Ix: Serial examinations; close monitoring for 24-48 hrs (Admit if unsure). Follow up at 1 month

Rx: Systemic steroids, O2, ventilation.

Control: Local ventilation (welders) in closed spaces.
Flushing of silos with fresh air. R-OEL: 3ppm (STEL 5ppm)
Ozone (O3):
Source:

[Note: same gas as stratospheric ("good") ozone, but in wrong place, viz. at ground level]

Clinical:
Acute: Chronic: "Lung aging", i.e. accelerated decline in lung function?

Ix/Rx: As for general respiratory measures.

Control:Readily reactive with most surfaces, (e.g. tubing) where it is converted to O2.
R-OEL: 0.1 ppm (STEL 0.3 ppm)
Ethylene oxide:
Source: Sterilising agent (health care workers!), fumigation chemical industry

Clinical: URT; skin irritant/allergen
Chronic:
     mutagenic
     clastogenic
     carcinogenic in animals
     ? carcinogenic (leukaemia)
     ?? teratogenic
(Revise these terms)

Ix/Rx: As per circumstances

Control: Enclosure/extraction. C-OEL: 5 ppm. Monitor exposed workers (See Task below).

Note: this is a problem in hospitals

Phosgene (COCl2):
Source: Chemical manufacture, heating chlorinated solvents, (chemical weapon)

Clinical:
Acute: Lower RT irritant (low solubility), ARDS, delayed pulmonary oedema.
Post-acute: lung function abnormality.

Ix: Suspicion, assess severity.

Rx: Observe, Rx early as for respiratory distress /pulmonary oedema.

Controls: Strict. R-OEL: 0.1 ppm

Glossary of lung injury:

Adult Respiratory Distress Syndrome (ARDS): diffuse parenchymal lung injury resulting in severe respiratory distress and hypoxaemic respiratory failure.
Bronchitis: Inflammation of the bronchial tree
Bronchiolitis: Inflammation of the bronchioles, i.e. the smallest branches of the bronchial tree
Alveolitis: Inflammation of the gas exchange part of the lung
Pulmonary oedema: Filling of the gas exchange part of the lung with fluid. Occurs with lung injury but also in heart failure
Emphysema: Breakdown of the gas exchange part of the lungs including the respiratory bronchioles, so that the alveoli become non-functional in that area.

Assignment: Hazardous gases

Question 1: Someone rushes in to tell you that there has been an ammonia leak and that one of the workers who was near the tank at the time has collapsed.

Outline ALL the steps needed in the management of this problem from an occupational health perspective. Include all the elements of a management system needed to deal with this sort of situation, including prevention of future episodes.

Question 2: What medical surveillance would you do, if any, for employees exposed to ethylene dioxide in hospital sterilising units?

REFERENCES:

  1. Occupational and Environmental Medicine,. La Dou J. 33, Pages 571-583. Gases and other inhalants.



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Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za. Last updated Jan 2007.
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