Microbiological growth on building materials critical moisture levels. State of the art

Transkript

1 Extracts from the report SP Rapport 2005:11 from 2005: Microbiological growth on building materials critical moisture levels. State of the art Pernilla Johansson, Ingemar Samuelson, Annika Ekstrand-Tobin, Kristina Mjörnell, Per Ingvar Sandberg, Eva Sikander SP Sveriges Provnings- och SP Swedish National Testing and Forskningsinstitut Research Institute SP Rapport 2005:11 SP Report 2005:11 ISBN ISSN Borås 2005 Postal address: Box 857, SE BORÅS, Sweden Telephone: Telefax:

2 2 Overview of the literature on microbiological growth on building materials in relation to critical moisture conditions Limits of the extract and study The selection of literature is based on the relevance to the question of the critical level for mould growth on the building materials. The extract includes the full list of the used literature and most of the text about the critical moisture condition as this part is most relevant for the work in IEA annex 41 Whole building heat, air and moisture response. The full report in Swedish can be found on SP web The first part of the text about mould has been cut down. As it is an extract for the use in IEA41 then some figures and or tables mentioned in the text can be missing, Important factors for mould growth Moisture and temperature For each mould species and temperature level there will be a minimal amount of moisture needed for the mould. This is described in isopleth diagrams as in figure 1 (Sedlbauer et al., 2002). Figure 1 Isopleths for species Aspergillus restrictus. Left: Isopleths for growing spores. Right: Isopleth growth of mycelium Figure from (Sedlbauer et al., 2002). Time dependence Besides moisture and temperature is the time a critical factor for microbiological growth The growth can divided in a number of phases. (Cooke et al., 1993).

3 3 Figure 2 Models of microbiological growth under ideal conditions. a) growth in a liquid with limited amount of nutrition b) colony growth on a material surface. Picture from (Cooke et al., 1993). Note the time lag for the start of growth. This is important for cases with a water damage or rain in the building period. For some materials is it possible to dry it out before microbiological growth starts. See (Chang et al., 1995). (Horner et al., 2001 for gypsum) (Johansson, 2003) Contamination or soiling A material that alone has a good mould resistance can still get mould growth from contamination or soiling on the surface. Literature: (Chang et al., 1996) (Grant et al., 1989). The soiling of material can give other problems that degradation of the material. Soiled wood Have a higher risk for creating a unpleasant smell than clean wood (Johansson, 1999). (Ekstrand-Tobin, 2003). High moisture levels with dry periods between The changing of the climate will have an influence on the growth. (Pasanen et al., 2000) Has made a review of previous studies ((Adan, 1994), (Viitanen, 1997)) (Johansson, 2003) showed that test on materials stored dry in a year with a previous mould attack got a more extensive attack at 95% RH than clean material. (Hallenberg et al., 1988) shoved that mould attack during the storing of the wood before building would give a higher risk for later mould growth. Testing mould resistance There are two types of methods that are normally used.

4 4 A. The material is exposed for a fixed climate (relative humidity and temperature) and exposed to the normal types of spores found naturally on the material. The growth of this mix of species can then be test. B. The material is exposed for spores from one or more known mould species. This is then placed in a fixed climate and the mould can growth. To prevent that spores on the material influence the result is the material sterilized before the testing. Different materials are attacked by mould in different extent and with different growth rate for the same climate. This makes it very difficult to compare measurement done in the laboratory and also to real exposures. Different species can attack different part of the material as for instance gypsum plates. The testing result can depend on the mould species that is used in the tests. See (Hyvärinen et al., 2002) (Doll et al., 2001) (Clarke et al., 1996) Measuring methods The methods used to quantify the mould attack on the tested material can be different as seen in this list used in the literature: 1. extension of mould on the surface (either based on what can be seen with the naked eye or by microscopic analysis), as. (Viitanen, 2001), (Johansson, 2002) 2. generation of CO 2 (Pasanen et al., 1992) 3. time for spore germination, as (Grant et al., 1989) 4. diameter on colony 5. number of (CFU) colony forming units /g material 6. total number of spores 7. amount of ergosterol in fungal cells All these methods have its limitations that will not be discussed here with one exception. Our evaluation is that testing a material only based on attacks seen with the naked eye gives a high risk of not finding mould growth on materials. It is for instance difficult to find mould on porous insulation materials without microscopic analysis. Mould attacks on reused materials was only seen by the naked eye in 17 out of 94 cases (18%) (Johansson, 2003). The conclusion is that selection of methods for quantification of mould attacks makes a comparison between studies difficult.

5 5 Critical moisture content previous values These are the values typically used in Sweden today without special evaluation. This is for wood for most other material no common recommendations is found. Table 1 Critical moisture content for wood and wood based materials (AMA, 2003) an Fukthandboken (The moisture handbook) (Nevander et al., 1994). Critical moisture content Reference For new materials, not more than 0,18 kg moisture/kg material (AMA, 2003) No risk <70 % RH (<0,15 kg/kg) (Nevander et al., Low to minor risk % RH (0,15-0,20 kg/kg)* 1994) High risk >85 % RH (>0,20 kg/kg)* * at temperatures where the microbial growth happens Recommendation for critical conditions for microbiological growth Definition of critical moisture condition Critical moisture conditions are the condition above which there is a risk that the material will degrade from microbiological contamination. The change can be gradual or sudden. The growth of mould will always come gradually depending on the type of mould, relative humidity, temperature, and type of surface, surface structure and time. It is therefore impossible to give a single fixed value. What is degradation of a material? The microbiological growth will come slowly and the growth is not also something that you can see with the naked eye. The growth can be seen in itself as a problem if it give us an unhealthy indoor environment. We have to look at where the mould grows and if gasses or particles can be transferred to the indoor air quality. Model for critical moisture condition in relation to damage/inconvenience of microbiological growth At studies of microbiological growth on materials is often found curves of the type: Level of mould growth Figure 7 t 0 time Typical curve for microbiological growth on material

6 6 Time t 0 until the microbiological growth starts and the slope of the curve are different for different materials, different temperatures and different relative humidity. We can change this to an equivalent time, defined as: t ekv = tid f RF f temp Δt This gives a more general result with a summation of relative humidity and temperature over time. The factor f RF describes the effect of relative humidity on the microbiological growth that is low below approx % RH and high at RH above %. Different mould species have different characteristics for different climate and nutrition levels. f RH 1 0 RH 1 RH % RH Figure 8 growth. The factor f RH describes the effect of relative humidity on the microbiological The factor f temp describes the effect of temperature on microbiological growth. Most species has an optimal growth at C. At low temperatures is the growth rate slower and at high temperature do it stop. f temp 1 0 Cold Hot Figure 9 growth. The factor f temp describe the typical effect of temperature on microbiological It is now possible to describe the rules so that

7 7 t ekv t 0 where t ekv is calculated for the lifetime of the building. It is easy to do by looking at figure 8 and see that the relative humidity is always below RH 1, and therefore f RF 0. These values are therefore the critical values that are given in the following table. It is possible to accept a slightly higher relative humidity at lower temperatures if we take into account the effect the variation in f temp as in figure 9. There is one more important factor that is important. It is the calculated equivalent temperature, t ekv, will have different values depending on if it a long period with high relative humidity or a summation of many short time periods with high relative humidity. Unfortunately do we not find systematic studies of mould on material and that gives us very few values to the formulas. We have to make our own evaluation based on the research results that we have found and the experience from SP damage investigations and test on materials. In the table have we evaluated that microbiological growth is damage/problem without looking on where the problem. In appendix have we tried to include the effect of the risk in the indoor environment from microbiological growth at different places in the building construction. Microbiological growth and the generation of gasses and particles from growing mould happen normally by change and without our control, so we have to accept that it is possible to have accurate moisture limits. It will always be an evaluation. Recommendations for critical moisture conditions Critical moisture conditions for microbiological growth is approx 75 % RF. Higher level can be found on some types of materials as seen the table based on the literature. Table 9 SPs recommendations for critical moisture conditions. Based on evaluations that the risk level is in the order of a few present. Material type Contaminated or soiled Wood and wood based Mineral wool insulation Expanded polystyrene (EPS) Critical moisture level [%RH] 75-80* Concrete * Experience/estimation from SP. Comments to the values in the table A. The values in the table are for long time exposure. B. The values are for the moisture conditions in the materials surface layer.

8 8 C. If the materials have been exposed of for instance rain or leakage is it necessary to treat the material. SPs experience is that the material must be dried out (to valued below the critical moisture condition) in a few days or weeks to prevent germination of spores and microbiological growth. For concrete will we recommend that the drying must be done in a few weeks or months. For gypsum boards gives the literature indication that the material must not be exposed to free water. D. The values in the table are for critical moisture content at normal room temperature around 20C. For wood and wood based materials is found in the figure the change in critical moisture condition with lower or higher temperature. We have not found similar figures for other materials. Figure 10 An overview of critical temperature and moisture levels for microbiological growth on wood and wood based materials from (Viitanen, 2004). E. The values in the table are for clean materials. If the material (for instance EPS) is contaminated will the mould resistance be lower and the values for contaminated materials must be used. The contamination or soiling can come from mishandling the material or from dust or particles in the air. F. If the moisture condition is above the critical level in the table is it not certain that we will get mould growth. But there will be a risk for mould growth. G. The literature study shows that there is not a definitive limit for growths for the listed materials. Different investigations on the same material can give different results. The testing methods are not the same and the materials in the same group can be different. A producer of a material can by investigations and testing give a higher level than in the table. H. It is possible to treat materials in different ways to get a higher critical moisture level, for instance by using fungicide treatment or substances that will reduce the mould growth. Such materials are not found in the literature. If producers will use these methods must the results be tested. In that case must also the long time effect of the treatment be evaluated. It must still work after years. I. An uncertainty is that material typically is tested at certain level as 75% (no growth) and 85% (here is growth). The difference in these levels is rather large. The uncertainty in the moisture measurement must also be evaluated. J. To be on the safe side that the critical values in the table is not exceeded in the building phase and the long time use it is recommended to put a safety factor on the critical moisture content. Evaluation of the risk in the building phase is important to reduce the risk for future damages.

9 9 Appendix 1 References for the different materials found in the literature sorted for the material types. ( The text in the table is not translated) Gypsum Referens Bakgrund/design Sammanfattning av resultat (Pasanen et al., 1992) 12 prover från byggnad påfördes sporer och inkuberades i 3 olika klimat under 31 dygn. CO 2 produktion ökade från och med dag 2 vid % RH (20-23 ºC). Ingen ökning kunde mätas vid % och % Dock visade odling ökande CFU- halter/g material. Man konstaterar att vid RF>82 % (Ritschkoff et al., 2000) (Horner et al., 2001) (Pasanen et al., 2000) (Doll et al., 2001) (Nielsen et al., 2000) (Fog Nielsen et al., 2004) Nya osteriliserade prover påfördes sporer och utsattes för olika klimat under28 veckor. Prover från byggvaruhandlare autoklaverades, doppades i sterilt vatten 10 min, påfördes sporer. Placerades i fuktkammare. Analyserades med stereomikroskop. Livskraften hos svampar testades vid olika torknings- och uppfuktningsförhållanden (fuktades upp genom att stå i vatten i 4 veckor, torkades ut under 7 veckor, hög luftfuktighet (95 %) 8 veckor, torkade 7 veckor). Prover för analys togs ut efter hand. Analyserade CFU, svampar och actinomyceter och totalantal sporer. Prover direkt från tillverkaren placerades i olika klimat (95 % RH, 0,1 Sat MC, 0,2 Sat. MC) under 5 veckor, varefter de analyserades med hjälp av mikroskop. 3 steriliserade (gammastrålade) prover påfördes sporer, inkuberades i 25 C i 70, 80 och 90 % Proverna fotograferades 1 gång/månad. Efter 7 mån genomfördes flera olika analyser. Steriliserade (gammastrålade) prover påfördes sporer. Flera olika RF och temperaturkombinationer. Digitalfotografering och stereomikroskop efter 7, 14 och 28 dagar, senare 1 gång i månaden till 4 eller 7 månader. Utbredning, artdiversitet, ergosterol, sekundära metaboliter och mykotoxiner analyserades. RF angrips materialet. Se Tabell 3. Vid 97 % RF och 23 ºC var angreppet på gipsskivan jämförbart med angrepp på träbaserat skivmaterial (particle board). Vid 90 %, 15 ºC fanns ingen växt. Vid 90 %, 23 ºC, detekterades växt efter 13 (28) veckor. Olika klimat redovisas, inga tabeller eller diagram, men hyfer växer på material vid 32 % RF efter 48 h. Efter 72 h har konidioforer bildats. Om materialet fuktas genom kapillärsugning kommer materialet att snabbt bli angripet. Inga gränsvärden konstateras. Olika arter växte på fram resp baksidan av gipsen (papp), samt på gipsen direkt. Trots att det är en stor variation på svampar som förekommer är gränsvärdet för deras minimiväxt 95 % genom kapillärsugning. Ingen växt kunde konstateras med hjälp av mikroskop, förmodligen pga svårigheter att analysera. Uppmätte ergosterol vid 90 % RF. Angrepp fanns vid 95 % RF. Fanns även angrepp vid 90 % RF, men då var dessa associerade till kontaminerade fibrer och partiklar.

10 10 Woodbased plate material Referens Bakgrund/design Sammanfattning av resultat (Ritschkoff et al., 2000) (Pasanen et al., 1992) (Pasanen et al., 2000) (Fog Nielsen et al., 2004) (Wang, 1992) Nya osteriliserade prover av tre skivmaterial (particle board, fibre board och plywood) påfördes sporer och utsattes för olika klimat under 28 veckor. Två typer av skivmaterial (plywood och fibre board) från byggnad påfördes sporer och inkuberades i 3 klimat %, % samt % RF under 3 veckor. Livskraften hos svampar på två typer av skivmaterial (particle board och wood board) testades i olika torknings- och uppfuktningsförhållanden. Steriliserade (gammastrålade) prover påfördes sporer och inkuberades i flera olika RF och temperaturkombinationer. Digitalfotografering och stereomikroskop efter 7, 14 och 28 dagar, senare 1 gång i månaden till 4 eller 7 månader. Utbredning, artdiversitet, ergosterol, sekundära metaboliter och mykotoxiner analyserades. Olika typer av skivmaterial (tre typer av fiberboards, två particle boards och en plywood) påfördes sporer, exponerades för olika kombinationer av RF (80, 85, 90, 95 % RF) och temperatur (7, 15, 20, 25 C). Se Figur 5. Proven möglade över 90 % RF. Har även testats vid 80 %, inga resultat publicerade från detta klimat. Lägre temp (15 ºC) och lägre RF medförde långsammare tillväxt. Se Tabell 3. Man konstaterar att angrepp finns över RF 82 %. Mellan 82 % och 96 % har det dock inte provats, så gränsen då det börjat växa kan ligga någonstans mellan 82 och 96 %. Man konstaterar att det finns en gräns för växt av mögel vid MC 20 % eller RF %. Ingen växt kunde konstateras vid 25 C och RF 69 %, dock fanns angrepp vid 78 %. Vid 20 C och 76 % kunde ingen växt analyseras, dock fanns angrepp vid 86 %. Vid 90 och 95 % RF angreps alla material vid alla temperaturer, vid 80 % bara vid 25 C. Concrete Referens Bakgrund/design Sammanfattning av resultat (Ritschkoff et al., 2000) (Viitanen, 2004) (Nielsen et al., 2000) Nya osteriliserade prover påfördes sporer och utsattes för 80, 90 och 97 % RF, 5, 15, 23 och 30 ºC, 28 veckor. Steriliserade (gammastrålade) prover påfördes sporer, inkuberades i 25 C i 70, 80 och 90 % Proverna fotograferades 1 gång/månad. Flera olika analyser genomfördes efter 7 mån. Se Figur 5. Vid 15 ºC och 90 % kunde ingen växt konstateras. Vid samma RF men 23 ºC : mkt liten växt efter 28 dgr. Vid 97 % RF växte mögel vid båda temperaturerna, men snabbare vid 23 ºC än 15 ºC. Angrepp vid % RF vid ytan, % djupare ner i materialet. Ingen växt vid något av klimaten.

11 11 Wood Referens Bakgrund/design Sammanfattning av resultat (Pasanen et al., 1992) (Fog Nielsen, 2002) (Viitanen et al., 1991) (Hallenberg et al., 1988) 12 prover från byggnad påfördes sporer och inkuberades i 3 fukttillstånd72-75 %, % samt % RF under 55 dagar. Steriliserade (gammastrålade) prover påfördes sporer och inkuberades i 25 C i 70, 80 och 90 % RF. Proverna fotograferades 1 gång/månad. Efter 7 mån genomfördes flera olika analyser. 6 prover påfördes sporer och inkuberades i olika klimat. Materialet inkuberades vid 65, 75, 85 samt 95 % RF. Se Tabell 3. Man konstaterar att angrepp finns över RF 82 %. Mellan 82 % och 96 % har det dock inte provats, så gränsen då det börjat växa kan ligga någonstans mellan 82 och 96 %. Kraftig växt vid 80 % RF. Ingen växt vid 75 % RF. 80 % lägsta RF där mögel växte. Fanns prover med riklig påväxt redan vid 75 % RF. Mineral wool and different insulation materials Referens Bakgrund/design Sammanfattning av resultat (Chang et al., 1995) (Chang et al., 1995) (Viitanen, 2004) (Fog Nielsen, 2002) Råd och rön (Konsumentverket, 2002) Kanalisolering av glasfiber (Fibrous glass ductboard) köpta i byggvaruhandel, steriliserades, påfördes sporer och inkuberades. Analyserades en gång per vecka i 6 veckor. Kanalisolering av glasfiber (flexible duct),, köpta i byggvaruhandel, steriliserades, påfördes sporer och inkuberades. Analyserades en gång per vecka i 6 veckor. Steriliserade (gammastrålade) prover påfördes sporer och inkuberades i 25 C vid 70, 80 och 90 % RF. Proverna fotograferades 1 gång/månad. Efter 7 månader genomfördes flera olika analyser. Olika typer av lösullsisolering sprayades med sporer och inkuberades i 95 % RF och 30 C. Ingen ökning av CFU g -1 vid 97 % RF (21 ºC). Uppfuktning av proverna medförde en ökning efter 1 vecka, men sjönk till ursprungsläget efter 3 veckor. Nedsmutsning ökade angreppens omfattning. Någon ökning av CFU g % RF (21 ºC) mest efter 3 veckor. Uppfuktning av materialet ledde till liten ökning, nedsmutsning till en ökning efter 21 dagar. Angrepp av mögel vid % RF efter lång exponeringstid (flera månader). Ingen påväxt kunde upptäckas vid något av klimaten. Sågspån av trä samt cellulosafiber som behandlats med brandhämmande angreps mest. Cellulosafiber med borsalter stod emot mögelangrepp bättre. Material av stenull och glasull angreps inte alls, eller i begränsad omfattning, beroende på fabrikat.

12 12 Wallpaper based on wood (Pasanen et al., 1992) (Grant et al., 1989) (Fog Nielsen, 2002) Referens Bakgrund/design Sammanfattning av resultat (Rowan et al., Prover av woodchip wallpaper autoklaverades, Analyserades efter 110 dagar, lägsta RF då 1999) påfördes sporer och placerades i varie- någon art kunde växa var vid 77,3 %, nästa rande klimat. 12 prover från byggnad påfördes sporer och inkuberades i 3 klimat under 55 dgr. Steriliserade (gammastrålade) prover påfördes sporer och inkuberades i 25 C i 70, 80 och 90 % RF. Proverna fotograferades 1 gång/månad. Efter 7 mån genomfördes flera olika analyser. art 82,2 % (20 ºC). Se Tabell 3. Tillväxt över 82 % RF. Se Tabell 2. Växt fanns vid 80 % RF. Underside roof panels Referens Bakgrund/design Sammanfattning av resultat (Chang et al., 1995) (Chang et al., 1995) (Horner et al., 2001) Tre typer av material användes, två nya och ett 10 år gammalt. Materialen innehöll en varierande mängd glasfiber. Proverna autoklaverades, påfördes sporer på ena sidan och inkuberades 28 dagar. Prover som ovan fuktades ner till 40 % MC innan de ympades, placerades i 70 % för att torka. Några av proverna placerades i fuktkammare med fläkt. Prover från byggvaruhandlare autoklaverades, doppades i sterilt vatten i 10 min och påfördes sporer. Placerades i fuktkammare. Analyserades med stereomikroskop. Se Tabell 4. Minsta RF för P.glabrum: mellan % för ökning 2-3 gånger av CFU g -1. Det var bara på det gamla materialet som alla tre arterna växte, detta tolkas som att det var mer känsligt. Hos det nya materialet fanns en undre gräns för växt vid % RF. Snabb upptorkning inom 3 dagar med fläkt gav ingen ökning av CFU g -1. Växt uppkom dock i fuktkammare utan fläkt. Olika klimat redovisas, inga tabeller eller diagram, men hyfer växer på material vid 32 % RF efter 48 h, först i öppna porer.

13 13 Appendix 2 Expected relative humidity and temperature in different building parts Expected relative humidity and temperature in different building parts for summer and winter conditions (Samuelson 1985). The values are based on the outdoor climate. Other moisture sources must be evaluated in the moisture design, that includes moisture from wet materials, rainwater coming in and so on. Cold ventilated roof - at the underside of roof consists of wood Winter % < 5 C Summer % >15 C Outer wall with bricks - on the outside of the wind barrier Winter % <5 C Summer % higher values after rain >15 C Wood floor on concrete slap with insulation between the concrete and the floor under the insulation at the concrete At the perimeter of the plate A distance from the perimeter Winter % 5-10 C Summer % ca 15 C Winter % ca 15 C Summer % C Ventilated crawl spaces at the underside of the floor construction Winter % <5 C Summer % >10 C

14 14 Appendix 3 The risk for indoor environment with different locations of the Microbiological growth The risk for people in the indoor environment from microbiological growth at different places in the construction. The risk for health effects from the expose in greatest if the source is found in the indoor environment and will be reduced if the source is away from the indoor. If the air can flow from the source to the indoor environment will the risk increase. If we have lower air pressure in the building in relation to the building part with mould will we have a risk for exposure to air borne ingredients from the damage. The risk of influence on the indoor environment from a microbial damage must be evaluated based on the damage site and the risk of airflow from source to the indoor environment. Examples on locations of the microbial growth and the risk for contamination of the indoor environment. Location of microbiological growth Roof ventilated with outdoor air Roof ventilated with outdoor air The lower part of the outer wall Crawl spaces Internal surfaces Conditions Overpressure indoors will increase the risk of damage but will prevent the air flow from the roof to the indoor Underpressure inside against the roof will eliminate the risk of damage from air convection. But the pressure difference will increase the air flow from the roof to the indoor environment Underpressure inside against the roof will increase the air flow from the lower parts of the walls to the indoor environment Underpressure inside against the crawl space will increase the air flow from the ground to the indoor environment High relative humidity at he surfaces. Example of cases No ventilation With balanced ventilation or system with only extract ventilation, the effect will be increased in windy conditions With balanced ventilation or system with only extract ventilation, the effect will be increased in windy conditions With all ventilation systems, the effect will increase in windy conditions Wet rooms, cellars without heating in the summer, sleeping rooms without enough ventilation, with high moisture production, with low outdoor temperatures Risk for indoor environment Low Middle Middle - High Middle - High High

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