How Healthy Is The Bedroom?
E. Hasselaar
1and J.T. van Ginkel
11OTB Research Institute for Housing, Urban and Mobility Studies, Delft University of Technology, P.O. Box 5030, 2600 GA Delft, The Netherlands
email: e.hasselaar@tudelft.nl
Summary: We spend 30-40% of our life time in the bedroom, well secured from the outdoor environment,
but is the indoor environment secure and healthy? The bedroom is probably the most important place in our home. While asleep, we do not act in control of the environment. It affects us, but in the morning we walk away from it. The paper focuses on the indoor climate of the bedroom. The bedroom is often poorly ventilated, full of house dust mite allergen, and with daily peak levels of other pollutants.
Keywords: indoor environment, bedroom, health risk exposure Category:healthy housing
1 Introduction
The study deals with the bedroom as a separate microclimate. We are exposed to the environment of the bedroom for more than one third of our lives. During the night, our bodies take a rest from the physical and psychic stresses of the day, we digest and emit metabolic waste and go through many other processes that are essential for long-term health. Undisturbed relaxation is the basis for quality of life [1]. A bedroom supports healthy sleep when it allows us to rest free from environmental stresses: noise, biological and chemical agents, overheating. TVOC sources are likely to be found in the bedroom, creating for instance a higher risk of asthma in infants [2]. People get up from their beds in the dark and walking in semi sleep creates risk of falling over obstacles. During the day, the senses stimulate active regulatory mechanisms to control the temperature and air quality. During sleep we smell and feel, but control of the environment is poor, while in the morning we tend to walk away from environmental stresses. The high levels of CO2 that are measured point at low ventilation rates. This paper describes the microclimate in the bedroom. The focus is on the moisture balance, air flow patterns and change rate and house dust mite allergen. The study results in indicators that mark the relation between housing, occupant behaviour and exposure to health risk in the bedroom.
In the major part of Dutch houses the volume of master bedrooms ranges between 30-40 m3. Moisture is produced by occupants and building related sources. Moisture is absorbed in the mattress, pillows, walls, etc., condensates on surfaces and is removed by evaporation in combination with ventilation. High moisture levels create a good environment for house dust mite. Exposure to house dust mite allergen is a major problem, as in 15-20% of the houses someone has allergic reactions to house dust. Growth conditions of mites depend mainly on relative
humidity and temperature. One study found that for D. Pteronyssinus the optimal conditions were 25 oC
and 80% RH, but these mites multiplied between 17
oC and 32 oC [3]. Above 85% mould toxins will
contaminate food supplies. Below the critical equilibrium level of 60-70% relative humidity (different per specie), and in general below 55%, mite will dehydrate and eventually die. Mite can survive in conditions that are considered hostile, provided there are pockets or regular periods with more favourable conditions, for instance in the bed. Mite can be dry-frosted [4]. The World Health Organisation suggests a safety threshold of 2 microgram of allergen protein per gram of house dust. Above this (pragmatic and not exact) level the conditions may trigger asthma attacks.
2 Method
Home inspection visits and interviews resulted in a database with 333 cases. The relations between occupancy, use of ventilation openings, moisture production and mould problems are analysed on the basis of these data, resulting in variables with strong correlations.
Air flow patterns
Particle distribution was monitored with particle counters in the size range of PM2,5 [5] and with smoke tests to illustrate air flow patterns with different inlet and exhaust systems and ventilation scenarios.
Moisture balance
The moisture balance for a dwelling is used to identify the activities and conditions that contribute to moisture related problems. The scenario presented in this paper is based on a household with two adults and three children in a single family dwelling. Two bedrooms are shared by two persons, one child has a private bedroom. The average air change rate of the house is set at 0.5 ACH and was differentiated per room. The exhaust volume for the central exhaust
Healthy Buildings 2006 Indoor Air Exposure
ventilation represents a practical situation: 1 of 24 hrs at high set point and the rest of the day at low set point. The kitchen exhaust is 21 dm3/s, bathroom 14
dm3/s, toilet 5 dm3/s at high set point, with 40% of these values at low set point. The (uncontrolled) emission of air from the crawl space is 2,5 dm3/s, RH
90% and T=13 0C. Outdoor air has 6 kg/dm3*10-6
moisture on average of day and night. House dust mite
163 dust samples were collected from mattresses and carpets of bedrooms and carpets and sofas of living rooms [4], [6] and [7]. The measured concentrations and variables were compared. Der p1 concentration of 2 µg/g dust was adopted as a threshold value to distinguish between high and low risk on HDM allergy. Correlations with housing characteristics were examined statistically on the basis of a part of the available data and resulted in models. The rest of the data were used to validate these models. These steps result in indicators that mark the relation between environmental conditions and exposure to health risk. Table 1 shows the structure of the model.
Table 1. Structure of the model
Agent concentration and exposure
Growth conditions Source indicators Emission indicators Transport indicators Concentration Exposure
Resulting exposure of occupant to concentration of agent
The resulting exposure is used to rank the health risk. Personal health effects are not measured.
3 Results
Air change rate
Night time ventilation is often quite low (air change rate of 0,2 – 0,5 ACH) due to (nearly) closed inlet openings. Ventilation behaviour is influenced by fear of draught and cold, sleep disturbance by noise from outside or from mechanical ventilation systems inside the house. According to the dataset, 44% sleep with closed grates or windows in the winter time and for the bedrooms of children this is even higher. In 43% of the houses the door of the bedroom or the connection to other windows does not permit a good flow to exhaust points. When occupants heat the bedroom the inlet openings stay closed for longer periods, while this effect is more obvious with only larger openings (sash windows) available. Given the small floor area and volume in social housing and also the higher occupancy rate, the available fresh air volume of 3-5 dm3/s is low compared to a standard
volume of 7 dm3/s per person, a volume that is
required to keep the human metabolic waste (=CO2) concentration at a constant level (C)2<1000 ppm).
Moisture balance
In a house with five persons the occupants produce in the used scenario 9 dm3 of moisture per 24 hours. The
building adds to the moisture level as well, in this scenario with 2,5 dm3 per 24 hours.
Table 2. Moisture production by occupancy
Moisture production in ml/24 hrs [dm3 *10-3 ]
Sleeping 8 hours (2, 1, 1, 1 person) 1240 Shower 2x morning 570 Washing at washbasin 1x 60 Tea making, use of water cooker 15 Cleaning floor and using kitchen sink 240 Watering plants (2x/week 1500 cm3) 500 One person present 8.00-16.00 hrs 600
Laundry 4 kg 30
Drying in attic 2000
Handwash 0,3 kg 50
Drying 0,3 kg on door rack 100 Three persons 16.00-18.00 hrs 450 Cooking between 17.30 and 18.00 500 Five persons 18.00-20.00 (22.00) 1200 Dishwashing 19.00, coffee 20.00 hrs 220 Two wet coats in hall 300 One shower around 21.00 hrs 400 One bath at 22.00 hrs 300 All wet towels in bathroom 200 Production by occupancy 8995 Building related moisture
production in ml/24 hrs [dm3 *10-3 ]
Moisture from crawl space 2200 Moisture from cavity in wall 300 Production by the building 2500
Table 2 presents the total for all rooms. The moisture level indoors varies per room and per period of time. The removal of moisture depends on the volume of air and the difference in vapour pressure. In the scenario for this study the total removal capacity is 14,7 dm3
per 24 hours. See table 3.
Table 3. Removal of moisture by ventilation
Removal of moisture by ventilation in ml/24 hrs [dm3 *10-3 ]
Total removal capacity 14676
The conditions are not stable, both production and removal are dynamic processes. During a large part of the day more moisture is removed than produced, except in the late afternoon and evening. The balance of separate room differs much from the balance of the dwelling. Figure 1 shows the balance between production and removal in three bedrooms. The balance is the sum of theoretical production and removal volumes; the values below the 0-axis show more removal than production. In practical conditions the moisture peaks will lead to 100% RH including
Indoor Air Exposure Healthy Buildings 2006
condensation in a certain space, until the production reduces and the space starts to dry. Figure 1 shows the production minus removal capacity without the complex processes that occur in a certain space.
Figure 1. Moisture balance over 24 hours in three bedrooms
The master bedroom (lowest line of Figure 1) is well ventilated with dry air from outside. Ventilation removes more moisture than is produced. The bedroom for the two children (topmost line) is ventilated with warm and moist indoor air and the moisture balance is effected by vapour transport from the bathroom and the living room.
Sleeping in aerosols
A monitor (PM2,5) was placed next to a bed of an adult sleeping person and recorded the aerosol mass concentration. Figure 2 shows how the aerosol concentration is related to sleep patterns and movements during sleep over a period of 9 hours. The inlet openings of the bedroom were closed. Temperature differences create air flow patterns. Cool inlet air drops from an inlet opening to the floor and is uplifted by the heat flux of persons in bed. This air flow secures the circulation of fresh air near the nose. Moving around in bed blows mattress dust including house dust mite allergen to the breathing area. The covers act as a blow pipe towards the nose. The figure shows body movements at short and longer intervals of approximately 1,5 hours and periods of quiet sleep [5].
Figure 2: PM2,5 concentration near the bed during sleep
House dust mite allergen concentration
The dataset average concentrations of Der p1 are: sofa: 1,3 µg/g (σ=1,6) (n=24), carpet: 3,78 µg/g (σ=9,3) (n=37), mattress: 6,48 µg/g (σ=9,8) (n=64). The average concentration of dust from the mattresses is high. Der p1 concentrations in mattresses are higher in multi–family (73% > 2 µg/g) than in single-family houses (45% > 2 µg/g), with 9,2 and 4,2 µg/g respectively. The number of persons in a house (occupancy load), thermal bridges and visible mould show the strongest correlation with house dust mite allergen concentration of >2 µg/g dust. Occupancy load is defined as the number of occupants divided by the number of rooms in the house. A separate group of data was used to test a model that uses occupant load as the predicting variable for high allergen concentration. In 76% of the cases the model prediction was good; 10% was predicted lower than measured and 23% was predicted higher than measured.
Table 4. Comparison of modelled and measured concentration of house dust mite allergen
model > 2 µg/g model ≤ 2 µg/g measured > 2 µg/g 45% 10%
measured ≤ 2 µg/g 22% 23%
The odds ratio of 5,45 (95% confidence interval and limit values of 1,75 and 69) result in a significant correlation between the occupant load and the allergen concentration. In only 10% of the houses in the second data set the occupant load predicted low Der p1 levels whereas the measured concentrations were larger than 2 µg/g. Occupancy load is a strong (proxy) indicator of exposure to house dust mite allergen. If the occupancy of a single-family house is larger than 1, an elevated risk on HDM allergy is likely to occur. For multi-family houses the occupancy only needs to be higher than 0,5 for an elevated risk level of HDM allergy to occur with great probability. Multi family houses are in general more air tight and smaller than single-family houses, which leads to higher moisture concentration.
4 Discussion
The experiments to study air flows and air change rates point at the importance of large inlet openings and overflow openings or exhaust openings in the bedroom to provide enough fresh air for a two person bedroom. The mechanical exhaust system has low impact on the flow through a bedroom, except when a stairwell creates a large stack effect and the door to the bedroom has a large opening (range of >200 cm2). The moisture balance shows that moisture removal with cool fresh air is important. High peaks in the house effect the moisture level in other rooms, especially in bedrooms that are cooler and poorly ventilated. The indirect effect of high moisture levels
-250 -200 -150 -100 -50 0 50 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 0,00 5,00 10,00 15,00 20,00 25,00 30,00 1 19 37 55 73 91 109 127 145 163 181 199 217 235 253 271 289 307 325 343 361 379 397 415 433 451 469 487 505 523 541 559 577 595 -0,0 0,00 0,01 0,01 0,02 0,02 0,03 0,03
Healthy Buildings 2006 Indoor Air Exposure
is (faster) growth of the population of house dust mite. Mould and moisture loving pest animals (sow-bugs, fish-moths) could add to the allergen level. Reliable data on the age of mattresses was not available and modelling of the age parameter was not possible. However, the age of the mattress is probably an indicator of allergen concentration as well. A new mattress does not contain house dust mite allergen. Because mites will grow in any mattress that is slept on during the warm and humid summer period, allergen material will accumulate in the course of a few years. All mattresses over five years of age (or 8 years with anti-mite cover) are very likely to contain allergen material above a concentration of 2 µg/g, with the potential to cause an asthma attack or even sensitization.
The health importance of the bedroom
In The Netherlands 2-5% of health loss is supposedly related to the physical environment [8]. Looking at the estimates for lung cancer, inflammation of the lungs, respiratory problems and accidents, an estimated 0,3 – 0,8 % of the total burden of disease is related to the bedroom. Better bedroom conditions can avoid 20-35% of this burden of disease [5].
5 Conclusion
The bedroom is not a healthy place, especially for persons with respiratory problems and sensitivity to house dust mite allergen. Health risk in bedrooms is indirectly caused by moisture production. Low air change rates are quite common. With poor ventilation all kinds of pollutants will build up and the exposure to allergen will increase. The moisture balance study shows that ventilation with cool fresh air is important and that high peaks somewhere in the house will effect the moisture level in bedrooms that are likely to be cooler and poorly ventilated with fresh air.
Growth conditions for house dust mite allergen are not strongly influenced by low air humidity or temperature. Despite few data available for validation, the age of the mattress supposedly is an important indicator of the allergen concentration. The resulting priority indicators of allergen concentration are: -the number of persons sleeping in bedrooms or the occupancy load of the house;
-the age of the mattress.
Secondary indicators that support the analysis of growth conditions and concentration of allergic dust are ventilation of mattress and covers and high ventilation levels leading to low winter temperatures (lower than 15 0C. The type of mattress (spring, foam,
water bed) is indicator of the amount of dust. The use of mite protective covers and dust removal by cleaning have a minor effect. Good ventilation during sleep reduces the allergen concentration in the bedroom air, but does not prevent exposure to dust blown from under the covers to the breathing area.
References
[1] Dahl R., The Regulation Of Sleep/Arousal. Affect and Attention In Adolescence: Some Questions And Speculations, Child And Adolescent Sleep Laboratory, Western Psychiatric Institute and Clinic. [2] Lehman, I. (2004) oral presentation on the relation between asthma and VOC exposure in children, WHO meeting in Vilnius, Lithuania.
[3] Pretlove S.E.C., et al. (2001) A combined transient hygrothermal and population model of House Dust Mites in beds, Platform presentation IAQ 2001, ASHRAE, San Francisco.
[4] Ginkel, JT van, Hady, M, & Hasselaar, E (2004). Quick scan to predict the concentration of House dust mite allergens in house dust. In X Bonnefoy (Ed.), Proc. 2nd WHO Int. Housing and Health Symposium (pp. 366-366). Bonn: WHO, European Centre for Environment and Health.
[5] Hasselaar E., Health performance of housing, indicators and tools, concept of thesis, publication expected in november 2006, Delft University of Technology, Delft.
[6] Koren, L.G.H. (1995) Allergen avoidance in the home environment: a laboratory evaluation of measures against mite, fungal and cat allergens, thesis, University of Technology Eindhoven.
[7] Boer, R. de and Kuller, K. (1997) Mattresses as a Winter refuge for house-dust mite populations, Allergy, vol. 52:299-305.
[8] Kamp, I. van, et al. (2002) Environmental Quality and human well-being. Outcomes of a workshop, RIVM, Utrecht.
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