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Case Study #2 - Large City Hospital

A large city hospital tested UV units to determine if ultraviolet lamps would effectively control microbial growth inside a large second floor air circulating system.

The test locations were both the down and upstream sides of the A/C cooling coil system. Testing was performed using SAB DEX Contact Plates. They first tested for unexposed surface fungi concentrations in the coil region. At each location the fungi (mold) were identified before UV exposure resumed.

One location on each side of the A/C coil was cleaned before tests started. Other parts on both sides were left uncleaned. It was determined that the locations had between 30 to 50 Culture Forming Units (CFU) of fungi (mold).

The short-wave ultraviolet lamps were then installed and tested for results. Both clean and uncleaned surfaces were tested for fungi to determine if the ultraviolet light would effectively eliminate surface contamination.

 

The next two tables show not only the CFU count before and after the UV installation, but identifies the type of fungi at each location.

Hospital Test Before Ultraviolet
Sample
Location
Results of A/C Coil
1
Downstream
 from coil
30* CFU per plate
3(10%) Alternaria
4(13%) Aspergillus Niger
3(10%) Bipolaris
20(67%) Cladosporium
2
Downstream
50** CFU per plate
3
Upstream 
from coil
50** CFU per plate
25(50%) Aspergillus Niger
25(50%) Cladosporium Rhizopus
4
Upstream
50** CFU per plate
* Colony Forming Unit
**Approximate count due to growth of Rhizopus
 

Hospital Test After Ultraviolet

Sample
Location
Results of A/C Coil
1
Downstream
from coil
2 CFU per plate
2
Downstream
(cleaned) 2 CFU per plate
3
Upstream
from coil
4 CFU per plate
4
Upstream
8 CFU per plate
1(13%) Aspergillus niger
2(25%) Aureo badidium
2(25%) Bipolaris
3(38%) Cladosporium
 

 

Conclusions

The ultraviolet lamps were very effective in controlling fungi on both the uncleaned and cleaned cooling coil surfaces. After the ultraviolet was installed, the fungi CFU’s per dish was zero at one location, two at another, four at the third and eight CFU’s at the last location.

Here is the killing rate break down:

At the coil downstream locations: the killing efficiency was 100% on the downstream-cleaned surfaces and 93% to 96% on the downstream-uncleaned surfaces.

At the coil upstream locations: the killing efficiency was approximately 84 % on the upstream cleaned and 92% on the upstream-uncleaned surface. The kill rate may be higher than reported due to the possibility of unexposed fungi entering the culture plates during sampling.

 

 
 

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