TAN DUNG LAM VAT LIEU XAY DUNG KHI THEO NGHIEN CtJU CONG NGHE Xtf LY MOT SO LOAI CHAT THAI CUA NGANH DAU

NGHIEN CtJU CONG NGHE Xtf LY MOT SO LOAI CHAT THAI CUA NGANH DAU KHI THEO H U O N G

TAN DUNG LAM VAT LIEU XAY DUNG

TS. NGUYEN QUOC BINH

Vien Ky thuat Nhiet ddi va BVMT TP Ho Chi M/nrt

Tom tat

Sao cao dwa ra mot so ket qua nghien ciru xir ly ve thanh phan, tinh chat cung nhw cong nghe xir ly bim khoan va tro thai sinh ra tir qua trinh dot chat thai cua nganh dau khi theo hwdng tan dung san xuat gach ngoi. Bwdc dau danh gia chat Iwgng san pham thu dwgc cho thay cong nghe co tinh kha thi. Tir do de xuat bien phap quan ly loai chat thai nay mot each phii hgp BVMT.

Abstract

The report presents researching results of technology in treatment of drilling mud and ash residues from combustion of oil-gas hazadous solid wastes to produce brick. As a first step, the results proclaimed this technology a practical method. Base on that some measures for ash management is proposed for environmental protection.

L m a DAU

Chat thai dau khi sinh ra tQ qua trinh khoan tham do va khai thac dau khi, vdi khdi lupng 6000 tan/nam day la chat thai nguy hai ed nguy CP gay ONMT cao. Trong thdi gian vQa qua Vietsovpetro da phdi hpp vdi nhieu co quan cd chQc nang de xQ ly chat thai. Phan Idn chat thai da dQpe tai che hoac dot tren Id dot hai cap tai Cty TNHH Sdng Xanh, Tinh Ba Rja - Vung tau. Tuy nhien, cho den nay hang tram tan hda chat dung djch khoan va tro sinh ra tQ qua trinh ddt rae dau khi van chua dupc giai quyet mdt each thet de, dang chd mpt bai chdn lap an toan.

- Chat thai co nguon goc la hoa chat dung dich khoan thai: Loai chat thai nay dang tdn dpng hang tram tan tai Cty TNHH Song Xanh. Dung djch khoan dupc chia lam 3 loai ehinh, phu thupc vao chat lam dung mdi (hay con gpi la pha mang): dung djch khoan gdc nude, dung djch khoan gdc dau va dung dich khoan gdc tdng hpp, trong dd Vietsovpetro sQ dung dung djch khoan gdc nude.

Bang 1: Thanh phan kim loai nang trong bun khoan Chi tieu

Cr Cd Pb Ni

Ndng dp (mg/kg) 0,7-160

0-0,1 0,4-200

0,3-44

Chi tieu

Cu Zn Mn Ti

Ndng dp (mg/kg) 0,52-69 0,25-85 0,5-300 20 - 500 (Nguon: Vien Ky thuat Nhiet ddi va BVMT)

He dung djch khoan gdc nude gdm 2 thanh phan chinh la nude va dat set va cac phu gia hoa chat khac.

Ket qua phan tich eae thanh phan dpc hai trong bun khoan lay tai bai chdn lap Nui Dinh va Cty Song Xanh cua chung toi trong nhieu dpt cho ket qua trong Bang 1.

• Tro thai: Tro sinh ra trong qua trinh dot chat thai bao gdm tro lang trong budng ddt (gpi la tro day) va tro bay theo khdi thai (gpi la tro nhe hay tro bay). Thanh phan cua tro phu thupe vao thanh phan chat thai dupc ddt va cdng nghe dot. Loai chat thai nay cung phat sinh ngay cang tang do hang ngay Cty TNHH Song Xanh van dot vai chuc tan chat thai. Hien nay ehi co mpt phan tro thai dupc Cty tan dung lam gaeh block.

Ket qua phan tich cac thanh phan kim loai nang trong tro tu qua trinh ddt rae dau khi tai Cty TNHH Sdng Xanh cua chung tdi trong nhieu dpt cho ket qua trong Bang 2.

Trudc day chung tdi da tien hanh nghien cQu cong nghe xQ ly cac chat thai nay theo hudng betong h6a[1,2].

Trong bao cao nay nhom nghien cQu thupe Vign Ky thuat Nhiet ddi va BVMT tiep tuc gidi thieu mdt sd ket qua nghien cQu xQ ly chat thai theo hudng tan dung lam vat lieu xay dung, cu the la dua vao thanh phan vat lieu de san xuat gach, gop phan hoan thien qua trinh xQ ly triet de chat thai dau khf, BVMT II. DOI TirUNG VA PHirONG PHAP NGHIEN CUiU

11.1. Ddi tupng

Odi tupng nghien cQu xQ ly gdm hai loai chat

KHOA H O C , CONG NGHE - CHUYEN GIAO

Bang 2: Thanh ot STT

1 2 3 4 5 6 7 8 9

Chi tieu

AI Cu Si Zn Ca Pb Mn Cd Ti

an kim loai trong mg/kg 3000 - 5000

30 - 3000 7000-10.000

28 - 220 1000-10.000

20-150 24-140 0 - 1 2 5000-1000

tro tif qua trinh dot rae dau khi

STT

10 11 12 13 14 15 16 17 18

Chi tieu

V Ni As Cr Sn Mo Bi Co Ag

Mg/kg

1-6

3-16 2 - 1 8 18-55 40-190

5-19 1-12

10 2,0

fWgudn; Vien Ky thuat Nhiet ddi va BVMT)

Bang 3: Thanh phan hoa hpc ciia dat set lam thi nghiem Thanh phan

SiO, TiOp

AI2O3

FesOa

FeO MnO MgO

%

61,54

1,07 19,35

8,43 0,31 0,00 0,53

Thanh phan

CaO

NajO

KpO

P2O5

MKN (do CO)

SO,

%

0,00 0,12 1,41 0,11 7,09 0,04

thai sau:

- Chat thai c6 ngudn gdc la hda chat dung dich khoan thai.

- Tro sinh ra tQ cac 16 dot rae dau khi.

11.2. PhUcfng phap nghien cuU

11.2.1. Nghien cuV san xuat gach tCfchat thai a. Nguyen lieu

- Dat set: Oat set dupc lay tU mpt Id gach thu cdng d Phudc An (Long Thanh, Odng Nai) vdi thanh phan hoa silicat dupc the hien trong Bang 3.

- Bun khoan va tro

Miu bun khoan va tro cd thanh phan hda ly dupc nghien cQu d Bang 1 va Bang 2.

b. Dung cu - thiet bi

Qua trinh thf nghiem dupe tien hanh vdi su hpp tac cua Id gach thu cdng Phudc An (Long Thanh, Odng Nai). Cac dung cu, thiet bj chinh gdm co:

- Chay va cdi.

-Can.

- 1 bp khudn 5cm x 5cm x 5cm.

-May trpn.

c. Cach tien hanh - Chuan bj miu

Oat set khi mang v6 phdng thi nghiem 6 trang thai ed thd tao hinh (dec: da dupc nghien va trpn nude). Nhung de chat thai (bun khoan d dang huyen

phu va tro d dang ran) ed the phan bd deu trong toan bp gach mau, chat thai phai dupc trpn vdi dat set d trang thai khd, mjn. Do dd, dat set dupe phoi that khd trong vdng 1 tuan, rdi dupe gia nhuydn bang chay va cdi trudc khi dem trpn vdi bun khoan va tro theo ty le trong Bang 4 va Bang 5.

Hdn hpp dat set va chat thai sau khi nhae trpn vdi nude dupc u trong vdng 4 ngay Qua trinh u dupc tien hanh bang each cho hdn hpp vao bao ni long bupc kin, de dat set trd nen dec va co the tao hinh.

Sau khi dupe tao hinh bang khuon 5cm x 5cm x 5cm, gach mau dupe phoi khd treng vdng 3 ngay. Thdi gian phoi dat y§u cau khi mau eua vien gach chuyen sang trang xam. Qua trinh phoi khd nham dam bao gach khdng bj nurt hoac nd trong qua trinh nung (do lupng nude bd'c hoi da giam), ddng thdi gach it bj bien dang trong qua trinh chuyen chd.

- Nung trong 16 gach

Gach kho dupc chd xudng 16 gach Phudc An, (Long Bang 4: Ti le phd'i trpn dat set va bun khoan

Ki hieu miu

BTO 81 82 83 84

Tile mCin khoan : dat set

mau dd'i chQng 1:10 2:10 3:10 4:10

Dat set

g

5000 5000 5000 5000 5000

Bun khoan

g

0 500 1000 1500 2000 Bang 5: Tile phoi trpn dat set va tro

Ki hieu mau

8T0 TIV

TII Till

Tile tro: dat set miu ddi chQng

1:15 2:10 3:10

Oat set

g

5000 3750 4000 3500

Tro

g

0 250 800 1050

Bang 6: Dp ben nen cua miu co chufa bun khoan

STT

1 2 3 4 5

Ki hieu mau

BTO

Bl B2 B3 B4

Dp ben nen (kN/cm^) 1,34 1,34 1,17 1,12 0,67 Bang 7: Do ben nen cua mau co chu'a tro

STT 1 2 3 4

Ki hieu mau

BTO

TIV Til

Till

Dp ben nen (kN/cm^) 1,34 3,53 2,49 2,27

Bang 8: Dp hut nifdc cQa mau co chu'a bun khoa sau 48 gid

STT 1 2 3 4 5

Ki hieu mau

BTO

Bl B2 B3 B4

n Op hut nude sau 48 gid(%)

20,23 21,68 22,10 22,24 26,34

Bang 9: Dp hut nwdc cua mau co chiia tro sau 24 gid

STT

1 2 3 4

Kihieu mau

BTO

BIV Bli

Bill

06 hut nude sau 24 gid(%) 20,07

16,68 16,73 16,06

Bang 10: Do hutnWdc cua mau co chua tro sau 48 gid

sn 1 2 3 4

Kihieu mau

BTO

BIV BII

BIII

Dd hut nude sau 48 gid(%) 20,23

16,34 16,81 16,10

Thanh, Odng Nai). Day la mdt Id gach thu cdng cd che dp nung nhu sau:

' - Giai doan 1: Xong 16 trong vdng 12 gid. Qua trinh gia nhiet xay ra cham de iupng nude cdn lai trong gach bd'c hoi tQtQ, tranh hien tupng nOt, nd vien gach.

- Giai doan 2: Cdn gpi la giai doan 'IQa Idn". Nhien lieu (cui) dupc cap vao Id lien tuc de nhiet dp trong 16 dupe duy tri d khoang 800°C trong vdng 12 gid.

- Giai doan 3: Ngung cap nhien lieu. Id dupc de nguoi tu nhien cho den khi ed the lay gach ra ngoai, thudng sau 24 gid.

L6 cao khoang 8m, gach mau dupe dat d tang tren cung, khoang 0,5m tfnh tQtren xudng.

11.2.2. Ket qua nghien cuV dp ben cQa vat lieu doi vdi moi trWdng

a. Kiem tra kha nang hoa tan tra lai kim loai nang trong nwdc mau gach thu dwgc

Sau khi kiem tra dp ben nen va dp hut nude, mau gaeh c6 pha bun khoan va miu gach cd pha tro, chpn miu gach CO dae tfnh co ly tdt nhat so vdi cac miu cung loai dd kiem tra tiep dp ben ddi vdi moi trudng song song vdi miu ddi chQng BTO.

Miu gach dupc chpn se dupc ngam trong nude cat vdi t^ le khdi lupng gach/khdi lupng nude cat la 1/10. Sau 1 tuan, 2 tuan, 3 tuan, 4 tuan nude ngam gach se dupc lay ra de xae dinh cae chi tieu kim loai nang Cu, Pb, Ni, Cr, Zn, Cd. Ndng dp cac kim loai nang nay dupc so sanh vdi Tieu chuan ve sinh (TCVS) ddi vdi chat lupng nude cap cho an udng va sinh hoat (505 BYT/QD, ngay 13/4/1992), va ddi chieu them vdi mpt sd tieu chuan nude udng cua nude ngoai nhu cija Co quan BVMT My EPA, Bp Y te va Phuc Ipi Canada va WHO.

b. Kiem tra kha nang hoa tan tra lai kim loai nang trong moi trwang co pH khac nhau

Cac bude thf nghiem dupc tien hanh tuong tu trong mdi trudng nude cat cd pha them dung djch CH3COOH 1N hoac dung djch NaOH 1N de eo cac pH thay ddi.

III. KET QUA NGHIEN CUU VA BAN LUAN

Mau gach thu dupc tU qua trinh tren dupc kiem tra tfnh nang CP ly [3,4,5]. Ket qua dupc trinh bay dudi day:

III.1. Danh gia tfnh nang cd ly cua vat lieu - Xae djnh dp ben nen cua gach theo TCVN 6355-1:

1998. Ket qua do dp ben nen cCia miu dua ra trcng Bang 6 va Bang 7

Nhan xet:

Vdi t^ le trpn bun khoan/dat set la 1/10, miu gach 81 cd dp ben nen tUPng duong vdi dp ben nen cua miu gach ddi ChQng. Khi ham iQpng bun khoan trong mau tang thi kha nang chju nen cua miu gaeh giam, co the trong bun khoan ed lin mdt ft dau va hda chat lan trong bun khoan.

Khi nhiet dp tang, lupng dau nay bde hoi nhanh rdi chay cung vdi su phan huy cua cac hda chat, lam cho cau true ben trong vien gach cd nhieu 15 rdng, gach co dp xdp cao se chju nen kem.

Op ben nen cua mau TIV (t;^ le tro/bCin khoan la 1/15) cao nhat trong bdn mau. Mac du d6 ben nen eCia miu gaeh giam khi lupng tro pha vao miu tang len nhung ca ba mau cd pha tro TIV (t<j le 1/15), Til (_t^ le 1/10), Till (t^ le 2/

10) deu CO dp ben nen cao hon mau ddi chQng. NhQ vay chQng to viec pha mpt lupng tro nhat djnh vao dat set se gdp phan nang cao kha nang chju nen cija gach. Dieu nay CO the dupc giai thfch do cac oxit kim loai trong tro eo vai tro nhu chat "nem" vao cac Id xdp trong cau true tinh the

KHOA H O C , CONG NGHE - CHUYEN GIAO

dat set lam cho vat lieu trd nen cQng chac hon.

111.2. Danh gia kha nang hut nUdc

Oe xae dinh dp hut nude (d nhiet dp thudng) cua vat lieu, Chung toi da thuc hien danh gia theo TCVN 6355- 3:1998. Ket qua kiem tra dp hut nude cua cac miu gach dua ra trong Bang 8, Bang 9 va Bang 10.

Nhan xet:

Dp hut nude cOa tat ca cac miu c6 pha bun khoan deu Idn hon dp hut nude cua miu ddi chQng khdng pha.

Khi ham lupng bun khoan trong mau tang thi dp hut nude CLia gach cOng tang theo, vi dau va hda chat bj phan hCiy trong qua trinh nung lam eau true ben trong gach cd nhieu Id rdng. Ket qua nay phu hpp vdi ket qua danh gia dp ben nen cOa mau vat lieu.

06 hut nude cua tat ca cac mau co pha tro deu nho hon dp hut nude cua miu ddi chQng kh6ng pha. Khi ham lupng tro trong miu tang thi dp hut nude cua gach tang khong dang ke. 06 hut nude cija gach ngam sau 24 gid va ngam sau 48 gid chenh I6ch rat it.

111.3. Ket qua nghien cufU dp ben cua vat lieu doi vdi moi trWdng

Bang 11: Nong dp kim loai hoa tan sau 3 tuan ngam gach trong nwdc cat (pH=6,5)

Chi tieu Dcrn vi

Cu

Pb Ni Cr Zn Cd

mg/l mg/l mg/l mg/l mg/l mg/l

BTO 0,002

<0,001

<0,001

<0,001

<0,001 0,001

81 0,001

<0,001 0,001 0,001 0,001 0,001 (Ghi ehii: KPH - khong phat hien thay) Bang 12: Nong dp Idm loai hoa tan sau 1 ngam dmol trwdng axitpH=2

TIV 0,004

<0,001

<0,001 0,006 0,004 0,001 tuan

Chi tieu Cu

Pb

Ni Cr Zn Cd Bang 13: l\

Ddn vi mg/l mg/l mg/l mg/l mg/l mg/l long dp kl/

BTO 0,12 0,053 0,083 0,033 0,28 KPHT Tl loai hoa

81 1.6

0,11 0,29 0,17

3.0

0,011 tan sau L

TIV 0,16 0,070

0,11 0,081

0,60 KPHT

? tuan ngam dmol trwdng axitpH=2

Chi tieu Cu

Pb

Ni Cr Zn Cd

Odnvj mg/l mg/l mg/l mg/l mg/l mg/l

BTO 0,20 0,04 0,12 0,05 0,44 KPHT

81

1.08 0,15 0,35 0,21 2.82 0,01

TIV 0,18 0,06 0,12 0,09 0,65 KPHT

Ket qua nghien cQu kha nang hda tan cija kim loai nang trong vat lieu trong mdi trudng nude khi thay ddi pH dua ra trong cac Bang 11 -^17.

Nhan xet

- TU cac ket qua thf nghiem dua ra trong eae Bang tQ 11 -^ 17 cho thay: ndng dp kim loai nang hoa tan tQ miu gach chQa tro cao hon ddi vdi miu chQa bun khoan (cd le do ham lupng kim loai nang trong tro nhieu hon trong bun khoan).

- Trong mdi trudng nude cd pH trung tfnh (nude cat), kha nang hoa tan trd lai cua kim loai trong gaeh hau nhu khdng eo. Ndng dp kim loai do dupe thap hpn nhieu lan so Bang 14: Nong dp kim loai hoa tan sau 1 tuan ngam dmol trWdng axitpH=4

Chi tieu

Cu Pb Ni Cr Zn Cd

Ddn vi mg/l mg/l mg/l mg/l mg/l mg/l

BTO 0,063 KPHT KPHT 0,011 0,027 KPHT

81 1.2

0,28 0,082 0,071

2.4

0,004

TIV . 0,13 0,037 0,067 0,037 0,24 KPHT Bang 15: Nong dp kim

dmol trwdng axltpH=

loai hoa tan sau 3 tuan ngam 4

Chi tieu

Cu Pb Ni Cr Zn Cd

Odn vi mg/l mg/l mg/l mg/l mg/l mg/l

BTO 0,13 KPHT KPHT 0,01 0,01 KPHT

81

0,98 0,17 0,08 0,07 2.00 0,01

TIV 0,10 KPHT

0,05 0,03 0,12 KPHT Bang 16: Ndng dp kim loai hoa tan sau 1 tuan ngam

dmol trwdng bazdpH=9 Chi tieu

Cu Pb Ni Cr Zn Cd

Bang 17: ^

Ddn vi mg/l mg/l mg/l mg/l mg/l mg/l Idng dp kit

BTO 0,07 KPHT KPHT KPHT KPHT KPHT V loai hoa

81

0,54 KPHT KPHT KPHT 0,76 KPHT tan sau 3

TIV 0,03 KPHT KPHT 0,04 0,01 KPHT tuan ngam dmol trwdng bazdpH=9

Chi tieu Cu

Pb

Ni Cr Zn Cd

Ddnvi mg/l mg/l mg/l mg/l mg/l mg/l

BTO 0,09 KPHT KPHT KPHT KPHT KPHT

81

0,64 KPHT

0,04 0,01 2.29 KPHT

TIV 0,02 KPHT

0,01 0,03 0,03 KPHT

vdi cac qui djnh tieu chuan nude udng cua Viet Nam va mpt sd nude tren the gidi.

- Trong m6i trudng c6 tinh axit hoac kiem yeu (pH tQ 5 -^ 9) thf kha nang hoa tan cua cac kim loai nang trong nude cung khOng dang ke, ndng dp kim loai do dupc thap hon nhieu lan so vdi tieu chuan nude cap cho an udng va sinh hoat (505 - 1992/BYT/QO).

- Neu ngam gach trong mdi trudng cd tfnh axft hoac bazo manh ( pH<2 hoac pH>11), thf kha nang h6a tan cua mpt sd kim loai se tang. Ket qua nghien cQu eua mpt sd tac gia khac eung da chQng minh dieu nay [ 6]

- So vdi cac phuong phap xQ ly khac (betdng hoa) thi phuang phap san xuat gaeh xay dung co kha nang bat glQ kim loai nang trong bun khoan va tro tdt hon.

IV. KET LUAN VA KIEN NGHj

- Od; vdi mau co chira dung dich khoan: vdi ti le khdi lupng bun khoan/dat set la 1/10, mau gach Bl cd dp chju nen va dp hut nude tuong duong vdi miu dd'i chQng khdng pha, viec sQ dung gach nay an toan ve mat moi trudng.

- Doi vdi miu co chira tro: vdi t^ le phdi trpn tro/dat set la 1/15, miu gach TIV cd kha nang chju nen cao hon 2.5 lan, dp hut nude thap hon 3% so vdi gaeh th6ng thudng, chQng to viec pha mdt lupng tro nhat djnh vao dat set CO the nang cao tinh chat co ly cua gach. Mae du ham lupng kim loai nang trong tro kha cao nhung khi trpn lam gach vdi ti le thfch hpp thi ham lupng kim loai

nang h6a trd lai khi gach dupc ngam trong nude cat va trong mdi trudng axit deu khong dang ke, an toan ve mat moi trudng khi sQdung.

- TQ ket qua nghien cQu tren cho thay co the sQ dung cac chat thai tren theo hudng tan dung lam nguyen lieu cho mpt sd 16 san xuat gach.

- Tuy nhien de dam bao an toan ve sQc khoe va moi trudng, chung tdi van khuyen cao kh6ng nen sQdung gach nay de xay be nude.

- Nghien cQu kha nang ap dung cdng nghe nay de xQ ly eho eac loai chat thai khac co thanh phan, tfnh chat tuong tu.

Tai lieu tliam Idiao

[1]. NguySn Quoc Binh. Ket qua nghien eiru dae tinh ciia tro thai sinh ra tir qua trinh dot chat thai nguy hai - Kien nghi bien phap quan ty. Tap chi phat trien khoa hoe cong nghe. DHQG TP.HCIt^. 12/

2004.

[2]. Nguyin Quoc Binh. Nghien ciru tinh chat eiia bun khoan va tro sinh ra tir qua trinh dot rae dau khi - Kien nghi bien phap quan ly. Hoi nghi khoa hoc cong nghe lan thir 8. DHBK - DHQG.

TP HCt^.2002. '

[3]. TCVN 1451(1998). Gach dae dat set nung.

[4]. TCVN 6355-1 (1998) - Gach xay. Xae dmh cirdng do nen.

[5]. TCVN 1655-3 (1998) - Gach xay Xae dinh do hiit nude.

[6]. Tran Thi Lien. Nghien eiru hoan thien cong nghe xirly bun khoan va tro tir qua trinh dot rae dau khi tam vat lieu xay dung.

Vien tJloi Trwdng va Tai Nguyen. 2009.Q

HIEU QUA Sir DUNG ...

(Tiep theo trang 17) can phai cung cap cae loai nut tai dam bao chat lupng bang each trudc khi SX hay nhap khau hang Icat nen sQ dung phuong phap REAT de danh gia hieu qua giam dn thuc te cua nut tai chdng dn. Ben canh do NSDLD nen td chQc cae Idp tap huan ve tae hai eua tieng dn va each phdng chdng tieng dn, trong dd nhan manh den vai trd cua viec sQ dung nut tai chdng dn, each sQ dung nut tai chdng dn dung de hieu qua giam dn dat mQc tdi da co the dat duoc.

Tai lieu tham Idiao

1 .Alberto Behar (2007), "Hearing protection devices: Adouble noise reduction rating", Official publication of the Canadian Acad- emy of audiolody

2. Berger E. H, RoysterL H., (1996), In Search of Meaning- ful Measures of Hearing Protector Effectiveness, 21" Annual Con- ference of the National Hearing Conservation Association, San

Francisco, CA, Spectrum Vol. 13, SuppL 1,p.29-32.

3. Berger E. H., Franks J. R., Lindgren F, (1996), "Interna- tional review of field studies of heanng protector attenuation". Sci- entific basis of noise-induced hearing loss, Thieme medical pub.

Inc. New York, pp.361-377.

4. Berger E. H. (2000), "The naked truth About NRRs", E-A- Rtog20.

5. Berger E. H. (2005), "Preferred Methods for Measuring Hearing Protector Attenuation", Congress and exposition on noise control engineering, Rio de Janeiro Brazil.

6. Directive 2003/10/EC of European Parliament and of the council (2003), Proposals for new Control of Noise at V/ork Regu- lations implementing the Physical Agents (Noise), pp. 134-139.

7. Health and safe guidelines Ontario (2007), "Appendix D-hearing protector (HPD) selection", Amendments to noise regulation for industrial establishments & oil and gas-offshore, pp.18-20.

8. Richard Neitzel, Sebrina Somers and Noah Seixas (2006),

"Variability of real-world hearing protector attenuation measure- ments", Occupational Hygiene 2006. 50(7), pp. 679-691. U