Air quality is one of the major environmental concerns in urban areas. In urban indoor environments, air can be more polluted than outdoor due to presence of various sources of air pollution, poor ventilation and building design and outdoor infiltration. People who spend their maximum time in those indoor spaces may get a significant exposure to various air pollutants (which may present either in gaseous or in particle form) through inhalation exposure routes and sometimes through dermal absorption. The EPA[1] states that a number of health risks are associated with the exposure to those indoor air pollutants, which could be temporary or permanent. The temporary health related symptoms are known as sick building symptoms (SBS). The case study identifies the potential hazards of increased levels of PM10, CO2 and Bio-aerosols in an underground metro station and tries to establish relationship between them. It also analyses the trend with respect to average concentration and percentage of the pollutants over a week. SBS score is also calculated for the building to establish whether the building is sick or healthy.

Hazard ID

Pollutants: Suspended Particulate Matter, PM 10, PM2.5; Source: Shedding, mechanical abrasion or natural anthropogenic; Effect: Aggravated asthma, decreased lung functioning, Respiratory irritation ,cardio

Pollutants: Carbon Dioxide; Source: Biological Activities, respiration; Effect: Dizziness, nausea

Pollutants: Bio aerosols; Source: Organic dust microbes, Living organisms; Effect: Allergies, Respiratory infection.

E. coli

Escherichia coli (E. coli) is a Gram-negative, facultatively anaerobic, rod-shaped bacterium of the genus Escherichia that is commonly found in the lower intestine of warm-blooded organisms used as markers for water contamination. Most E. coli strains are harmless Transmission /Exposure routes : Fecal-oral route, and most illness has been associated with eating undercooked, contaminated ground beef, swimming in or drinking contaminated water, and eating contaminated vegetables; but direct person-to-person contact can also spread infection, according to Jacobson[2].


The genus Bacillus is a gram-positive, rod-shaped bacterium that is known to form endospores under stress conditions. Bacillus bacteria thrive on dead or decaying organic material. The spores are normally found in soil, dust and water. High levels of Bacillus species in the indoor air generally indicate previous water damage and lack of adequate maintenance of the building or house. Occupants of moisture-damaged buildings suffer from irritations of the eyes, illnesses of the upper and lower respiratory systems, tiredness, faintness, allergies, and neurological problems, according to Kosa[3].


Staphylococcus is a genus of Gram-positive bacteria. Under the microscope, they appear round (cocci), and form in grape-like clusters. Staphylococcus is found virtually everywhere, and usually does not result in infection. It is very common on skin, and can also be found in the nasal passages, throats, and hair of 50% of healthy individuals. Food poisoning and skin infections, as well as toxic shock syndrome, are among the illnesses caused by Staphylococcus, according to Murray[4].


1. To establish a relationship between parameters (Bio aerosols, PM10, CO2, Temperature, RH) measured inside metro station.

2. To analyze a trend of each microbial population measure at platform area in metro station

3. To find the chances of getting lung infection due to exposure of the subjects to the given microorganism.

4. To modify the given questionnaire for the underground metro station.

5. To compute the SBS score separately for male and female staff of different age groups. 6. To suggest the control measures in case the building is identified as sick

Exposure Assessment

1. Source  

• Environmental Scientific Group[5] define it as a substance which is located in, on or under the land and has the potential to cause harm to human health, water resources or the wider environment

2. Pathway

• The means or route by which a source of contamination can migrate; an identified receptor can be exposed to, or be affected by an identified source, according to Environmental Scientific Group[5]. In order for microorganisms to release indoor bio aerosols, they must get indoors, grow and multiply on some material and then get into the air. Microorganisms can get indoors through the heating, ventilation, and air conditioning system , door, window, cracks in the walls, the potable drinking water system, or be brought in on the shoes and cloths of people working or visiting in the building. Water, humidity, temperature, nutrient sources and oxygen determine whether microorganisms will grow in the indoor environment.

3. Amount:

• The amount of exposure of the pollutants to people at platform of metro station is given in Table 1. The concentration was recorded over 8 hour cycle.

Table 2: Hours average data of PM10, Bio aerosol, CO2, Temperature and RH at platform area Monitoring cycle PM10 Bio aerosol CO2 TEMP RH

Cycle-1 (06:0am to 02:0pm) 237.7125 318 439.2313 21.5663 39.29

Cycle-2 (02:0pm to 10:0pm) 352.2913 179 658.9725 22.1263 40.455

Cycle-3 (10:0 pm to 06:0am) 409.26 123 653.95 22.195 40.7375

• The concentration of Bacillus as compared to E. coli and staphylococcus is seen to be the highest on all days of the week.

• The concentration of Bacillus is highest on Saturday and Monday which can be associated to increased footfall (Figure 3)

• The average concentration of microbes is seen to the highest on Monday due to rush after the weekend as depicted by Figure 4

4. Duration

• The peak hours at Delhi metro are from 2pm to 10pm. The footfall is comparatively less from 6am to 2pm. The metro shutdown at 11pm to 6am

Table depicts the relationship between various parameters. The PM10 andC02 concentration, Temperature and RH is seen to be gradually increasing as the footfall increases. The rise in level of CO2 is very drastic as compared to other parameters. Rise in temperature and RH is very low.

• The concentration of bio-aerosols is seen to be reducing as the foot fall increases (Figure 5)

Dose Response

Daily inhalation volume (m3): 0.81*body mass (kg) Assumed average body mass of metro worker =60 kg Daily inhalation volume= (48.6/3) m3 =16.2m3

Bacillus Anthracis - Exponential (Druett, 1953)

Average Amount of pathogen inhaled daily =6600.42 cfu

Probability of Death = 10.32 %

Escherichia Coli - Beta –Poisson (Cornick & Helgerson[6]) Average amount of pathogens inhaled=3645 cfu Probability of positive stool isolation due to E.coli =2.14%

Staphylococcus - Exponential (Rose and Haas[7]) Average amount of pathogen inhaled = 3126.52 cfu Probability of lung infection = 0.023%

Risk of lung infection for 300 working days/year = 6.66%

Risk Characterization

The model shows separate analysis for man and women as significant effect of gender is observed on prevalence of SBS. The Answers of SBS symptoms in questionnaire are reported as ‘often’, ‘sometimes’, or ‘never’.

• “Often” – If more than 20% occupants says - 1-3 times/ week or almost everyday or everyday. Score assigned = 1

• “Sometimes” - If more than 20% occupants say - 1-3 times / month or almost every week. Score assigned = 0.5

• “Never” – if < 20% occupants complain. Score assigned = 0

Sick Building identification The total SBS score will be reported in 0-6 scale.

• If total score is = or > 3, building’s IAQ is unacceptable and it is “sick”

• If total score is = or < 1, building’s IAQ is acceptable and it is “Healthy”


	Age under 20	Age between 20- 39	Age between 40-59


Symptoms Male (12) SBS Score Female (10) SBS Score Male (23) SBS Score Female (15) SBS Score Male (9) SBS Score Female (3) SBS

Score Irritation in the eyes (%) 19c 0 24a 1 14c 0 25b 0.5 52a 1 55a 1

Irritation in the nose (%) 31b 0.5 23a 1 21b 0.5 43b 0.5 27b 0.5 52b 0.5

Dryness in mucous (%) 16 c 0 18a 1 41b 0.5 53b 0.5 61b 0.5 75b 0.5

Lethargy/drowsiness/tiredness (%) 43b 0.5 29a 1 49 a 1 58a 1 72a 1 81a 1

Dryness on the face/hands (%) 23a 1 14a 1 63b 0.5 37 a 1 27b 0.5 42b 0.5

Headache (%) 37b 0.5 25b 0.5 49 a 1 65 a 1 56b 0.5 78b 0.5

Total SBS Score 2.5 5.5 3.5 4.5 4 4


The table depicts the sick building score for different age groups. The score is seen to be higher in all age groups for women. There might be a gender difference in reporting rates of sick building syndrome because women tend to report more symptoms than men do. Along with this, some studies have found that women have a more responsive immune system and are more prone to mucosal dryness and facial erythema. Also, women are alleged by some to be more exposed to indoor environmental factors because they have a greater tendency to have clerical jobs, wherein they are exposed to unique office equipment and materials (example: blueprint machines), whereas men often have jobs based outside of offices), according to Godish[8]. Highest score is for women under the age of 20

Risk Management & Communication

Measures to be followed to reduce risk at metro station: 

1. Relocate any fresh air intakes to avoid pulling in outside contaminants from garbage bins .

2. Follow the maintenance schedules on HVAC systems.

3. Increase the Minimum Efficiency Reporting Value (MERV) rating of air conditioning filters to the highest level acceptable for the AC system.

4. Minimize copy toner and other chemical use in office space.

5. Purchase office furniture with low or no formaldehyde and other volatile organic compound (VOC) emissions.

6. Use low VOC paints for remodeling or decorating.

7. Vacuum floors using equipment with HEPA (high efficiency particulate air) filters.

8. Respond to any leak in the plumbing system, roof or windows within 24 hours and thoroughly dry any moist materials to prevent mold growth.

9. Store chemicals in a central location with adequate ventilation to the outside.

10. Use natural or organic janitorial cleaning and pest control products

Risk communication

Risk communication is an interactive process of exchange of information and opinion on risk among risk assessors, risk managers, and other interested parties.

Risk communication is an integral and ongoing part of the risk analysis exercise, and ideally all stakeholder groups should be involved from the start. Risk communication makes stakeholders aware of the process at each stage of the Risk Assessment. This helps to ensure that the logic, outcomes, significance, and limitations of the Risk Assessment are clearly understood by all the stakeholders. Information may be available from the stakeholder. Industry stakeholders may, for example have unpublished data crucial to the risk assessors, which may be an essential part of the data needed for the risk assessment. There is also information that is typically presented to the stakeholders (both industry and consumers), as an integral part of the risk analysis process, according to World Health Organization[9].

Risk communication to employees

• At the average observed concentration of PM10 of 332.89 ppm there might be a chance of getting minor acute throat infections since standard limits 260 ppm (NAAQS) are be crossed.

• At the average concentration of 224.62 CFU/m3 of E.Coli there is 97.86% of NOT having any presence of ambient air E.coli in Stool sample.

• At the average concentration of 192.995 CFU/m3 of staphylococcus there are 93.34% chances of NOT getting lung infection for a worker working 300 days a year and 8 hours a day.



Escherichia coli
Staphylococcus aureus