Do Walk Off Mats Reduce Lead Dust in the Home?

If there is enough lead in the dust, it can cause permanent damage

Goal: The Center was hired by the City of Cambridge, Massachusetts to conduct a study to determine whether walk-off mats provided to tenants after lead hazard control treatment reduce the amount of lead dust within the home. The study began in March 1998 and continued until December 31, 2000.

Description: After treating dwellings using funds from the HUD Lead Hazard Control Grant Program, units were randomly assigned to a "program mat" treatment group or to a control ('no mat") group. Units that had a tenant mat present when the unit was first visited after treatments were assigned to a "tenant mat" group. After treatment and again one year later, dust wipe samples were collected from 4 floor locations: just inside and outside the primary entryway to the unit: 5 ft. inside the units in the direction tenants were expected to walk routinely when entering the units; and on the opposite side of the room. The same locations were sampled at both visits.

Results: Study results for the 65 enrolled units indicate that the Cambridge lead program was effective in treating homes. One year after treatment, floor dust lead loadings inside the door never exceeded 100 /ft² , and only 7 units had loadings above 40 /ft² ; only 5 units had floor dust lead loadings inside rooms above 100 /ft² and only 9 units had lead loadings that exceeded 40 /ft^2. Results for the initial visit after treatment, however, were higher than expected. The geometric mean loadings often exceeded clearance limits even though clearance testing had been performed an average of 31 days before. These high results were possibly due to the postponement of cleaning in common areas until after all units in multifamily buildings were treated, leading to track in problems.

Of the 65 enrolled units, 23 had complete data adequate for use in the mat study: 6 "no mat" units, 7 "program mat" units, 6 "tenant mat" units, and 4 "gain mat" units (i.e., those that had no mats at first visit but had mats one year later). The crucial expectation of the mat study was that one year after intervention, bare floor dust lead loadings inside the home of "program mats" and "tenant mat" units would be less than those in "no mat" units. Results indicate that mats may have had a slight effect on dust lead loadings inside homes. One year after intervention median floor dust lead loadings inside the door of "program mat" and "tenant mat" units were 17 /ft² and 10 /ft², respectively, whiled that in "no mat" units was 31 /ft². Just after intervention, however, inside-door dust lead loadings for "program mat" units were higher than those of "no mat" units, complicating data interpretation. It was not possible to draw firm conclusions due to the small dataset and the slight changes observed. Low loadings observed in mat units one year after treatment may have been due to the presence of mats (which reduce the amount of tracked-in lead contaminated dust and soil), to the differences between units in each category just after treatment, or to differences in house cleaning practices (i.e., people who routinely use mats also keep their house cleaner than those who do not routinely use mats.) 

Conclusion: Because mats are inexpensive and may aid in preventing track-in, it was recommended that programs consider distribution of mats after lead treatments, educating tenants about maintenance and periodic replacement to prevent mats from becoming exposure sources themselves. 

^{For more information, please contact Jill Breysse at jbreysse@centerforhealthyhousing.org}

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