Issue 3 Publication Date 15 March 2002
Bags, Desiccant, Silica Gel and Bags, Desiccant, Activated Clay
AMENDMENT RECORD
Amd. No
Date
Text Affected
Signature and Date
REVISION NOTE
This standard is raised to Issue 3 to update its content, in accordance with the requirements of Defence Standard 81-41 and Defence Standard 00-00 (Part 2)/2. Reference to Agreed Industry Standard and testing have been removed.
HISTORICAL RECORD
This standard supersedes the following: Defence Standard 81-68 Issue 2 Defence Standard 81-68 Issue 1 CPU/CON/205-1 UK/SC/3460 UK/SC/3272
dated dated dated dated dated
April 1998
September 1988 July 1984 August 1976 March 1975
DEF STAN 81-68/3
CONTENT
Description
Content Preface Main Text
SECTION 1 GENERAL
1 Scope 2 Warning
3 Related Documents 4 Definitions
5 Information to be Supplied by the Purchaser 6 Material Requirements 7 Manufacture
8
Test Requirements SECTION 2 PACKAGING
9 Packaging of Desiccant Bags
10 Storage and Use of Packaged Desiccant 11 Marking
Table A Bags Filled with Silica Gel Table B Bags Filled with Activated Clay Table C Tests of Bag Material Table D Moisture Uptake Limits
Table E Summary of Shelf Life Requirements
ANNEX A Determination of Resistance to Dropping and Dusting
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Page 1 2 3
3 3 3 4 4 4 5 5
8 8 9 6 6 7 7 10 11 DEF STAN 81-68/3
PREFACE
Standards for Defence
Bags, Desiccant, Silica Gel and Bags, Desiccant, Activated Clay
a. This Defence Standard specifies bags filled with either silica gel or activated clay for use in Services desiccated (Defence Standard 81-41 (Part 2), Method II) packaging by the Ministry of Defence (MOD). b. This standard has been produced by the Defence Packaging Authority (D Pkg A), Defence Logistic Organisation (DLO) /Corporate Technical Services (CTS). c. This standard has been agreed by the authorities concerned with its use and is intended to be used whenever relevant in all future designs, contracts, orders etc. and whenever practicable by amendment to those already in existence. If any difficulty arises which prevents application of the Defence Standard (Def Stan), the Directorate of Standardization (DStan) shall be informed so that a remedy may be sought. d. Any enquiries regarding this standard in relation to an invitation to tender or a contract in which it is incorporated are to be addressed to the responsible technical or supervising authority named in the invitation to tender or contract. e. Compliance with this Defence Standard shall not in itself relieve any person from any legal obligations imposed upon them. f. This standard has been devised solely for the use of the Ministry of Defence (MOD) and its contractors in the execution of contracts for the MOD. To the extent permitted by law, the MOD hereby excludes all liability whatsoever and howsoever arising (including, but without limitation, liability resulting from negligence) for any loss or damage however caused when the standard is used for any other purpose.
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DEF STAN 81-68/3
TEXT
Standards for Defence
Bags, Desiccant, Silica Gel and Bags, Desiccant, Activated Clay
SECTION 1 1
GENERAL
SCOPE
This Defence Standard specifies requirements for the manufacture, performance, testing and storage of bags filled with either silica gel or activated clay for use as a drying agent inside a water vapour-proof or water vapour-resistant barrier for MOD packaging. 2 WARNING The Ministry of Defence (MOD), like its contractors, is subject to both United Kingdom and European laws regarding Health and Safety at Work, without exemption. All Defence Standards either directly or indirectly invoke the use of processes and procedures that could be injurious to health if adequate precautions are not taken. Defence Standards or their use in no way absolves users from complying with statutory and legal requirements relating to Health and Safety at Work. 3
RELATED DOCUMENTS
3.1 The publications shown below are referred to in the text of this standard. Publications are grouped and then listed in alphanumeric order. Designation BS 2540 BS 3266
Title
Specification for Granular Desiccant Silica Gel
Methods of Test for Determination of Conductivity, pH, Water Soluble Matter, Chloride and Sulphate in Aqueous Extracts of Textile Materials
Specification for Desiccant Activated Clay Specification for Beaded Desiccant Silica Gel Packaging of Defence Materiel
BS 7529 BS 7554 Def Stan 81-41
3.2 Reference in this standard to any related document means in any invitation to tender or contract the edition and all amendments current at the date of such tender or contract unless a specific edition is indicated.
3.3 In consideration of 3.2 above, users shall be fully aware of the issue and amendment status of all related documents, particularly when forming part of an invitation to tender or contract. Responsibility for the correct application of standards rests with users. 3.4 DStan can advise regarding where related documents are obtained from. Requests for such information can be made to the DStan Help desk. How to contact the help desk is shown on the outside rear cover of Defence Standards.
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DEF STAN 81-68/3
SECTION 1 4
GENERAL
DEFINITIONS
For the purpose of this standard the definitions given in Def Stan 81-41 apply, otherwise the following shall apply for the purposes of this standard.
4.1 Basic Desiccant. This is a desiccant that adsorbs 27 % of its dry mass when in equilibrium with an atmosphere maintained at 50 % Relative Humidity (RH) and 25°C. 4.1.1
Silica Gel when conforming to BS 2540 and BS 7554 meets this definition.
4.1.2 Activated clay, conforming to BS 7529, will adsorb 20 % of its dry mass under these conditions. This means 1.35 times more activated clay by mass is required to provide the same desiccant performance as the ‘Basic Desiccant’ or Silica Gel. 4.2
For the purposes of this standard a Hermetic Seal is an Airtight Seal.
4.3 For the purposes of this standard an impermeable material is one with a water vapour transmission rate of zero, e.g. metal or glass.
4.4 Re-lifing or Relifing. The assessment of desiccant to establish whether viable and likely to remain so for a stated period. 4.5 4.6 4.7 5
Reactivation / Regeneration. The re-processing of spent desiccant for re-use. % m/m. Percentage Mass Fraction calculated as per clause A.2.5.
Bulk Containers. For this standard this shall mean containers of over 100 kg. INFORMATION TO BE SUPPLIED BY THE PURCHASER
The purchaser shall state clearly in his contract or order, the type and amount of desiccant required, the relevant NATO Stock Number(s) (NSN) and the number of this Defence Standard. 6
MATERIAL REQUIREMENTS
6.1 Bags. The bags shall comprise of one or two layers of flexible, water vapour-permeable materials.
6.1.1 When made up, shall be suitable for use at temperatures of (-13 to +55) °C and under reduced pressure (reducing steadily from (760 to 230) mm Hg in 30 minutes). 6.1.2 The material shall be cut so that when pressed flat the dimensions of the made-up unfilled bag are within the tolerances shown in Tables A and B.
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DEF STAN 81-68/3
SECTION 1 GENERAL
6.2 Desiccant. As supplied, it shall not be regenerated / reactivated product. Calculations in military packaging are based on ‘fresh’ desiccant and reused desiccant often has an uncertain effective life. Reactivated desiccant may be acceptable in transit packs, when marked for disposal afterward. 7
MANUFACTURE
7.1 Each bag shall be filled with Silica Gel, (BS 2540, BS 7554) or Activated Clay, (BS 7529) in accordance with Tables A and B respectively.
7.1.1 When filled, the bag shall be capable of being pressed into close contact with two external right-angled faces joined by a 20 mm radius without any signs of splitting. When an outer layer of material is used, it shall fit closely to the inner layer without any undue compression.
7.1.2 When filled with desiccant each bag shall be capable of holding at least 30% more than the charged mass.
7.1.3 Closure may be achieved by sewing, stitching, heat-sealing or high frequency welding using reinforcing materials when required. 8
TEST REQUIREMENTS
8.1 All samples taken from any portion of the bag material shall comply with the requirements of Table C.
8.2 The filled bags shall comply with the following requirements:
8.2.1 Moisture Uptake. The moisture uptake of the filled bags shall not be less than the limits specified in Table D, when assessed as follows.
a. Test Conditions. An atmosphere maintained at (50 ± 2) % RH at (25 ± 2) °C, with an air velocity of approximately 0.3 ms-1.
b. Method. Samples are removed from their container and hung freely exposed for exactly four hours.
8.2.2 Resistance to Dropping. When tested by the method described in ANNEX A, there shall be no visible deterioration of the bags.
8.2.3 Resistance to Dusting. After being subjected sequentially to the procedures for dropping and bumping as described in ANNEX A, the mass of dust collected from outside a bag shall be less than 0.02 % of the gross dry mass of the filled bag.
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DEF STAN 81-68/3
SECTION 1
GENERAL
Table A - Bags Filled with Silica Gel - Commonly Used Sizes
NATO Stock Number
4440-99-
220-2652 224-6989 224-6990 224-6991 224-6992 224-6993 224-6994 224-6995 220-2718
Table B - Bags Filled with Activated Clay - Commonly Used Sizes
NATO Stock Number 4440-99- 220-4122 225-3064 225-3065 220-4123 220-4124 220-4125 220-4126 220-4128
Desiccant Content
g Amount Of Activated Clay
6.8 13.5 20.3 33.8 67.5 135.0 337.5 675.0
Basic Desiccant Equivalent
5 10 15 25 50 100 250 500
Size of Unfilled Bag
mm Width 54 ± 2 60 ± 2 65 ± 2 72 ± 3 88 ± 3 110 ± 4 125 ± 4 150 ± 4
Length 108 ± 4 120 ± 4 130 ± 4 144 ± 6 176 ± 6 220 ± 8 250 ± 8 300 ± 8
Desiccant Content
g
5 10 15 25 50 100 250 500 2500
Size Of Unfilled Bag
mm WIDTH 54 ± 2 60 ± 2 65 ± 2 72 ± 3 88 ± 3 110 ± 4 125 ± 4 150 ± 4 320 ± 10
LENGTH 108 ± 4 120 ± 4 130 ± 4 144 ± 6 176 ± 6 220 ± 8 250 ± 8 300 ± 8 380 ±10
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DEF STAN 81-68/3
SECTION 1
GENERAL
Table C - Tests of Bag Material Test
pH of water extract
Chloride calculated as NaCl.... % m/m
Table D - Moisture Uptake Limits
Silica Gel % m/m 14.0 10.0 9.0 8.0 6.0 4.5 3.0 2.0 1.0
Desiccant Content or Basic
Desiccant Content
g 5 10 15 25 50 100 250 500 2500
11.0 10.0 8.0 7.0 5.5 4.0 2.5 2.0 -
Activated Clay
% m/m
Limit 5.0 min 8.0 max.
Method BS 3266
0.05 max. BS 3266
Sulphate, calculated as Na2SO4... % m/m 0.25 max. BS 3266
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DEF STAN 81-68/3
SECTION 2 PACKAGING
9 PACKAGING OF DESICCANT BAGS
9.1 Unless the form of packaging is specified in the contract or order the product shall be supplied in sound, clean, dry and airtight sealed containers suitable for the product. 9.2 All packaged desiccant shall have a shelf life stated by the supplier / manufacturer. This shelf life shall be clearly and prominently marked on the package.
NOTE The usability of desiccant stock depends on the quantity of moisture adsorbed before actual use. This will depend on the; the moisture content as supplied, the container itself and the quality of its seal, how many times the container is opened and resealed adequately and the ambient conditions when opened and when in storage. Care should be taken on these variables. Note that containers made of impermeable materials should have the longest shelf lives their weak point is usually their seal. Most materials used in packaging (e.g. fibreboard, polyethylene etc.) permit ingress of moisture at varying rates. Most commercial packs are permeable, even if apparently airtight, and this must be considered if long term storage is required. 10
STORAGE AND USE OF PACKAGED DESICCANT
10.1 When any desiccant container is opened the desiccant should be used as soon as possible. It is recommended that containers should be opened for the shortest possible time and preferably in a controlled low % RH area. It is also recommended that any plastic bags involved should be heat/fusion re-sealed. No desiccant shall be used beyond the manufacturer shelf life without re-lifing. Relifing shall only be done where economic, small quantities may cost less to replace than test, and only by an accredited laboratory / test house
10.2 Containers of up to 2.5 kg of desiccant with no manufacturer / supplier stated shelf life shall be assumed to have a shelf life of not greater than one year from date of manufacture. All such container’s contents must be used immediately on opening. Non-impermeable containers with more than 2.5 kg (but not a bulk container) can be re-sealed for future use, up to the ‘Use By’, date and may be considered for re-lifing.
10.3 Impermeable hermetically sealed containers, or permeable bulk-containers, with no stated shelf life shall be considered to have an unopened shelf life of five years in a dry storage area. Above this period the material shall be re-lifed at least annually, or before use. 10.4 Impermeable hermetically sealed containers that cannot be hermetically resealed once opened shall have a maximum content’s shelf life of one year from date of opening. Unless the material is re-lifed, the shelf life shall also not exceed five years from date of manufacture.
10.5 The shelf lives noted here are based on experience and best practice for a Temperate Climate, where a Tropical Climate applies the shelf lives should be halved.
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DEF STAN 81-68/3
SECTION 2 PACKAGING
10.6 A Summary of the Shelf-life requirements is shown in Table E. 11
MARKING
Each desiccant bag and airtight container shall be legibly and durably marked according to statutory requirements and with at least the following:
11.1 Desiccant bags
Designation Silica Gel, or Silica Gel (beaded), or Activated Clay Defence Standard (specification): Def Stan 81-68
Mass of Basic Desiccant (or basic desiccant equivalent) (g) NATO Stock Number (NSN) Date of Manufacture (DoM) DD/MM/YYYY Contractor's Identification Name, Initials or Recognized Trade Mark 11.2 Containers
Designation; Bags, Desiccant, Silica Gel, or
Bags, Desiccant, Silica Gel (beaded), or Bags, Desiccant, Activated Clay
Defence Standard (specification): Def Stan 81-68 Mass of Desiccant (kg) Service Prefix 0462 (Navy), H4 (Army), 40D (Airforce) NATO Stock Number (NSN) Lot or Batch Number Quantity of Contents (x Bags of y g (or kg)) Date of Manufacture (DoM) DD/MM/YYYY Manufacturers Shelf Life (Use By) DD/MM/YYYY Contractor's Identification; Name, Initials or Recognised Trade Mark
11.3 All containers shall be marked or labelled with the text “ONCE OPENED THE CONTENTS MUST BE USED AS SOON AS POSSIBLE”
11.4 Where storage or use in a tropical climate is expected the following text shall be applied “THIS PACKAGE IS SHELF-LIFED FOR TEMPERATE CLIMATE, THIS IS HALVED FOR TROPICAL STORAGE. ONCE OPENED, EVEN IF RESEALED, THE MATERIAL SHOULD BE USED AS SOON AS POSSIBLE”. Otherwise, an appropiate ‘Tropical Use By’ date shall be used.
11.5 In use those who open a container shall label or mark them as having been opened and on what date, e.g. “First Opened on DD/MM/YYYY”, if they are to be resealed. If Relifed, they shall also be marked as follows, “Relifed until DD/MM/YYYY”.
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Table E - Summary of Shelf Life Requirements Pack Construction
Unopened Storage / Shelf Opened Storage / Shelf Life
Additional Shelf Life Marking
Life
Permeable (e.g. Fibreboard / Manufacturers Shelf Life Use Immediately plastic-bag / sack), pack and (usually one year)
impermeable (metal / glass)
-
containers. Up to 2.5 kg contents † Permeable Packs above 2.5 kg Manufacturers Shelf Life
Until manufacturers ‘Use by Relifed Until Date (if applicable) contents †
Date’ (Consider re-lifing) Permeable pack Bulk Containers Manufacturers Shelf Life, (if
A maximum of one year from On opening, Date of Opening not stated Five years from date first opening but not more than Relifed Until Date (if applicable)
of manufacture), before re-five years from date of lifing required, unless
manufacture.
otherwise specified as less by manufacturer / supplier.
Impermeable Packs (metal/glass) Manufacturers Shelf Life, (if If resealable hermetically, five On opening, Date of Opening containers. Above 2.5 kg contents not stated Five years from date
years from date of manufacture, Relifed Until Date (if applicable) of manufacture), before re-before re-lifing / disposal.
lifing required
If not resealable hermetically,
On opening, Date of Opening shelf life is a maximum of one A Label as per clause 10.4 year from first opening but not more than five years from date of manufacture.
NOTE 1: The above assume a temperate climate, if tropical all shelf lives shall be halved. NOTE 2: Dates shall be in the format DD/MM/YYYY.
NOTE 3: If containers prove non-fully hermetically resealable, contents may be transferred to one which is, and then Re-lifed. NOTE 4: † Where no shelf life / use by date or date of manufacture is applied then shelf life is assumed to be one year.
DEF STAN 81-68/3 10 DEF STAN 81-68/3
ANNEX A
DETERMINATION OF RESISTANCE TO DROPPING AND DUSTING
Carry out the following tests at a temperature of not less than 15 oC and a maximum of 75 % RH. A.1 Drop Test
Drop the bag twice through a distance of at least one metre onto a smooth, level steel plate so that it lands first on the edge containing the seam constructed after filling and second on the opposite edge. Visually inspect. A.2 Bump Test
A.2.1 Using a fine camel hair brush, remove any dust adhering to the outside surfaces of the bag. Determine the mass of the bag, as used for the Drop Test, to 0.01 g (m1)
A.2.2 Place the bag in a dust free metal drum having a smooth interior finish and a closely fitting lid. The diameter of the drum shall not be less than the width of the unfilled bag, and its length shall not exceed the length of the unfilled bag by more than 50 mm. A.2.3 Secure the drum vertically to the platform of a bumping machine and subject it to a bump of not less than 40 gn applied 180 times per minute, for exactly 30 minutes. Allow the drum to stand for at least 10 minutes.
A.2.4 Open the drum and, using a fine camel hair brush, carefully collect any dust adhering to the surfaces of the bag and to the inside of the drum. Determine the mass of the dust to 0.001 g (m2).
A.2.5 Calculate the percentage of dust from the formula below:
Dust, % m/m = m2 x 100
m1
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© Crown Copyright 2002 Copying Only as Agreed with DStan
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Contract Requirements
When Defence Standards are incorporated into contracts users are responsible for their correct application and for complying with contractual and statutory requirements. Compliance with a Defence Standard does not in itself confer immunity from legal obligations.
Revision of Defence Standards
Defence Standards are revised as necessary by up issue or amendment. It is important that users of Defence Standards should ascertain that they are in possession of the latest issue or amendment. Information on all Defence Standards is contained in Def Stan 00-00 Standards for Defence Part 3 , Index of Standards for Defence Procurement Section 4 ‘Index of Defence Standards and Defence Specifications’ published annually and supplemented regularly by Standards in Defence News (SID News). Any person who, when making use of a Defence Standard encounters an inaccuracy or ambiguity is requested to notify UK Defence Standardization (DStan) without delay in order that the matter may be investigated and appropriate action taken.
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