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April 2024 Occupational exposure to sewer gases among informal sanitation workers in Nairobi, Kenya Sylivanus Obiero

© WaterAid/ James Kiyimba

In Nairobi, Kenya, informal sewer workers face significant health risks due to exposure to hazardous gases like hydrogen sulphide (H2S) and carbon dioxide (CO2). A study conducted by Kenyatta University's Department of Environmental and Occupational Health (DEOH) revealed elevated gas levels in sewer facilities, posing short- and long-term health threats.

In Nairobi, Kenya, up to 60% of the population live in informal settlements, many relying on pit latrines, septic tanks, manholes and other onsite sanitation methods. This presents challenges for sewer management. Informal sewer workers play a vital role in emptying faecal matter and keeping the environment clean at the household level. In areas with no formal sewer systems and those that are inaccessible by mechanical emptying trucks, sewer workers provide a viable alternative to emptying, transport and disposal of faecal matter. However, this often involves direct contact with faecal matter, without personal protective equipment (PPE) and reliable safety measures. Working in confined spaces, exposes workers to elevated levels of poisonous gases such as hydrogen sulphide (H2S), carbon dioxide (CO2), methane and ammonia, leading to  injury, sickness and even death.

As part of an initiative to secure the rights of all sanitation workers, a research team from Kenyatta University Department of Environmental and Occupational Health (DEOH) assessed occupational exposure levels to H2S and CO2 gases by workers employed in informal emptying sites in Mathare, Kibra, Ruaraka, Embakasi South, and Dagoretti North sub-counties of Nairobi County.

Map of the study area- Nairobi City Council

Map of the study area- Nairobi City Council

This cross-sectional analytical study used structured questionnaires with 259 sewer workers, including emptiers of manual and mechanical pits, septic tanks, manholes and cesspits, and recorded gas levels at the facilities.

Participants reported exposure to sewer gases along with other hazards associated with manual emptying. One said: “When emptying faecal waste from pit latrines and unblocking sewers we often experience stench smell from the gases. One worker collapsed while attempting to unblock a manhole from the gases inside which caused the collapse”. Exposure to elevated levels of sewer gases causes both short- and long-term health effects for workers. Short-term effects of mild and moderate exposure to CO2 (<15000ppm) include headaches, drowsiness and mild respiratory stimulation), with long-term health effects including body inflammation and uneasiness. Exposure to CO2 at higher levels causes suffocation and death. For H2S, short-term effects of moderate exposure (<10ppm) are nausea, headaches, loss of sleep, fatigue and dizziness. Long-term moderate exposure can cause inflammation, distress and convulsions. Immediate exposure to elevated levels (>100ppm) can result in loss of smell, pulmonary oedema and instant death.

The study showed that 35% of sites had higher levels of H2S gas (PEL-TWA <10ppm) and 40.9% had higher levels of CO2 gas (PEL-TWA <5000ppm). Cumulatively, more than half of informal sewer workers experienced higher levels of exposure to these gases. The majority of sites with these higher levels were pit latrines and manholes, as poorly ventilated, partially full, shallow pit latrines (up to 7ft deep) create the perfect anaerobic conditions for gas formation with consequent negative health effects.

Partially full and full pit latrines at Korogocho Informal Settlement

Partially full and full pit latrines at Korogocho Informal Settlement

Occupational training teaches workers about health and safety risk identification, safety procedures and ways to mitigate and prevent these risks. Findings showed a lack of training among the majority (81.9%) of informal sewer workers. This was attributed to the informal nature of their work, a lack of official recognition, and insufficient support from sanitation actors such as the government and Non-Governmental Organizations. One worker at Gitaturu, Korogocho noted: “It’s important for organizations to come to our rescue and train us like when Nyumba Kumi and Community Health Promoters (CHPs) are trained from time to time”.

Manual sewer workers were exposed to higher levels of sewer gases (75.9%) compared to mechanical sewer workers (24.9%) as they worked in confined spaces, physically lifting, carrying and handling faecal matter. This also exposed them to the risk of cuts, fractures and musculoskeletal disorders.

Based on this study, recommendations to improve working conditions for informal sewer workers include:

  1. Prioritising training on sewer gases and effective prevention and mitigation measures.
  2. Providing tools to reduce manual emptying and direct contact with the hazards of sewer gases.
  3. Recognising and formalising their work and working environments leading to initiatives to improve their dignity, safety and health outcomes.
  4. Providing health checkups to combat the stigma associated with manual emptying.

Additional recommendations include the provision of appropriate PPE, such as ventilators, to protect against inhaling gases. A legal framework and policy provisions exist that detail occupational exposure levels to gases, however, greater awareness is needed of preventative safety policies and best practice.


Acknowledgments: This research study was conducted as part of a Master's Degree in Occupational Health and Safety from Kenyatta University, School of Health Sciences. Special gratitude to the support provided by the faculty and staff in the Department of Environmental and Occupational Health and Safety Led by supervisors Dr Antony Wanjohi and Dr Peterson Warutere. It was made possible through a research grant from the Initiative for Sanitation Workers.