table of contents seasonality our business experiences seasonality that varies by product line . because more construction and do-it-yourself projects occur during the second and third calendar quarters of each year in the northern hemisphere , our security product sales , typically , are higher in those quarters than in the first and fourth calendar quarters . however , our interflex business typically experiences higher sales in the fourth calendar quarter due to project timing . revenue by quarter for the years ended december 31 , 2015 , 2014 and 2013 are as follows: .
considering the year 2015 , what is the percentage of reserves for environmental matters related to remediation of sites?
2015 fourth quarter revenue includes the full-quarter impact of the acquisitions of simonsvoss , axa and milre . employees as of december 31 , 2015 , we had more than 9400 employees , approximately 26% ( 26 % ) of whom have the terms of their employment covered under collective bargaining agreements . this includes non-management european employees who are represented by national and local works councils . environmental regulation we have a dedicated environmental program that is designed to reduce the utilization and generation of hazardous materials during the manufacturing process as well as to remediate identified environmental concerns . as to the latter , we are currently engaged in site investigations and remediation activities to address environmental cleanup from past operations at current and former manufacturing facilities . we are sometimes a party to environmental lawsuits and claims and have received notices of potential violations of environmental laws and regulations from the u.s . environmental protection agency ( the "epa" ) and similar state authorities . we have also been identified as a potentially responsible party ( "prp" ) for cleanup costs associated with off-site waste disposal at federal superfund and state remediation sites . for all such sites , there are other prps and , in most instances , our involvement is minimal . in estimating our liability , we have assumed that we will not bear the entire cost of remediation of any site to the exclusion of other prps who may be jointly and severally liable . the ability of other prps to participate has been taken into account , based on our understanding of the parties 2019 financial condition and probable contributions on a per site basis . additional lawsuits and claims involving environmental matters are likely to arise from time to time in the future . we incurred $ 4.4 million , $ 2.9 million , and $ 2.1 million of expenses during the years ended december 31 , 2015 , 2014 , and 2013 , respectively , for environmental remediation at sites presently or formerly owned or leased by us . as of december 31 , 2015 and 2014 , we have recorded reserves for environmental matters of $ 15.2 million and $ 8.8 million . of these amounts $ 2.8 million and $ 2.4 million , respectively , relate to remediation of sites previously disposed by us . given the evolving nature of environmental laws , regulations and technology , the ultimate cost of future compliance is uncertain . available information we are required to file annual , quarterly , and current reports , proxy statements , and other documents with the u.s . securities and exchange commission ( "sec" ) . the public may read and copy any materials filed with the sec at the sec 2019s public reference room at 100 f street , n.e. , washington , d.c . 20549 . the public may obtain information on the operation of the public reference room by calling the sec at 1-800-sec-0330 . also , the sec maintains an internet website that contains reports , proxy and information statements , and other information regarding issuers that file electronically with the sec . the public can obtain any documents that are filed by us at http://www.sec.gov . in addition , this annual report on form 10-k , as well as future quarterly reports on form 10-q , current reports on form 8-k and any amendments to all of the foregoing reports , are made available free of charge on our internet website ( http://www.allegion.com ) as soon as reasonably practicable after such reports are electronically filed with or furnished to the sec . the contents of our website are not incorporated by reference in this report. .