G GL AM-NHAA 052 – 2016 (September 2016)

澳 門 特 別 行 政 區 政 府 Governo da Região Administrativa Especial de Macau 衛 生 局 Serviços de Saúde

Prevention of Hydrogen Sulfide Intoxication due to Exposure in Indoor Areas

General information Hydrogen sulfide (H2S) is a flammable, colourless hazardous gas soluble in water. Heavier than air, it tends to concentrate in low-lying or poorly ventilated areas. It is present naturally in crude oil, natural gas, volcanic gases and hot springs, and can be formed in bacterial decomposition of organic matters as well as industrial activities. Relatively high concentration of hydrogen sulfide can be found in poorly ventilated areas with decayed substances, such as marshes, sewers, drains, tunnels, shafts, pits and caves, and these substances are the wastes generated in decomposition pertaining to human or animal activities. The appearance of hydrogen sulfide in commercial or residential buildings is mainly associated with the configuration, cleaning and maintenance of the system. Overflow of hydrogen sulfide from the drains and its subsequent accumulation in indoor areas may directly or indirectly result from blockage or poor ventilation in pipelines, improper cleaning, improper use of drain cleaners, absence of stench traps in drains or of water in the traps, or poor indoor ventilation among other situations.

Effects of hydrogen sulfide on human body Hydrogen sulfide is a fatal gas. Normally a small dose (at 10ppm or below) does not trigger any symptom, and it is highly noticeable because of its distinctive ‘rotten egg’ odour. However, individuals with long exposure to the odour will suffer from olfactory fatigue, unable to detect a possible rise in concentration levels and poisoned unknowingly. The toxicity of hydrogen sulfide increases with higher concentration level and longer exposure time. A 50ppm concentration may cause dryness and irritation in the mucosa of nasopharynx, and a concentration of 100ppm can lead to temporary olfactory loss. Concentration over 200ppm can cause acute irritation in the eyes and the respiratory tract, as well as dizziness, headaches and sleepiness. Hydrogen sulfide which concentrates at an extremely high level (of over 530ppm) can result in coma, apnea or even death within a short period of time.

Common situations leading to high hydrogen sulfide concentration in indoor areas of a building  Accumulation of a large number of sulfide compounds in the public sewage system (including sewer, , pit, etc.) over a long period of time; massive formation and accumulation of hydrogen sulfide and other hazardous gases in the system without adequate ventilation.  High concentration of hydrogen sulfide may escape from the sewer if a large amount of detergent, disinfectant, or is poured into it within a short time.

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 Drain equipment (connecting washbasin, , bathtub, shower tray, water closet and floor drain) is not fitted with any stench (such as U-shaped ) in its outlet pipe, the trap fails to hold water properly (to form a water seal), or the connecting parts between the stench trap and the grease interceptor/manhole or trunk sewer are not enclosed to effectively prevent backflow of sewer gases;  Hydrogen sulfide which overflows from the sewer is not discharged due to poor ventilation in indoor areas.

Occurrence of two or more of the aforesaid situations often accounts for the accumulation of hydrogen sulfide at hazardous levels.

Key points in prevention of hydrogen sulfide intoxication Daily hygiene:  There should be a stench trap installed under the floor drain and regular addition of clean water (at least once a week) to ensure sufficient storage of water in the bottom curve (water seal) of the trap for prevention of sewer gas backflow.  An exhaust fan, for example, should be installed to maintain good ventilation of indoor areas.  Detergent, disinfectant, bleach or drain cleaner should be used properly. The chemical products should not be poured into the drains directly before they are diluted according to instructions for use, and they should not be used together. The user should keep a distance from the drain outlet when using any of the said products to avoid inhaling chemical fumes subsequently released. A large amount of clean water should be poured into the drains 25 minutes after the drain cleaner is used so as to clean and remove chemical remnants from them. Clothing such as gloves and an apron are recommended to prevent the solution from contacting the skin. Good air ventilation must be maintained in the process.  Be more alert; flush the drains with water once an odour comes out.

Building construction, maintenance and management:  All drain equipment (connecting washbasin, sink, bathtub, shower tray, water closet and floor drain) should be fitted with a stench trap appropriately, and there should be enclosed connecting parts between a stench trap and a grease interceptor/manhole or trunk sewer.  Sewage pipes (especially the horizontal pipes) should be cleaned regularly to prevent accumulation of organic and other waste.  Ventilation of the public sewer of a building should be improved to prevent the formation of an anaerobic environment and accelerate discharge of gases accumulated in the pipe.  Stench trap(s) should be installed in the public sewer of a building to prevent backflow of odour and other gases to indoor areas;  Wherever conditions allow, the inclination of horizontal drains should be increased to accelerate discharge of sewage and reduce waste accumulation;  Cleaning of drains, sewers and areas that may be filled with hydrogen sulfide must be executed with adequate ventilation.

Occupational safety precautions:  Standard personal protective equipment and alert safety systems must be used in the process of cleaning , septic tanks, sewers and so on. Adequate ventilation must be ensured for the sites where the work is undertaken. 2/3

In case of an accident/ suspected intoxication, you must: 1. Keep calm; 2. Leave the site immediately (or escort severely exposed persons) and relocate to places with good ventilation and loosen your clothing; 3. Call the Fire Services Bureau for help as soon as possible; 4. Immediately evacuate people from the sites to prevent them from being poisoned; 5. Not enter the poisonous sites without suitable protective equipment to perform rescue or other activities.

Centre for Disease Control and Prevention Health Bureau Revision (2016.9)

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