Revenue Recognition  We generate revenue primarily from manufacturing and selling a comprehensive line of safety products to protect the health and safety of workers and facility infrastructures around the world in the oil, gas and petrochemical, fire service, construction, utilities and mining industries. Our core safety products include fixed gas and flame detection instruments, breathing apparatus where SCBA is the principal product, portable gas detection instruments, industrial head protection products, firefighter helmets &amp; protective apparel and fall protection devices. Our customers generally fall into two categories: distributors and industrial or military end-users. In our Americas segment, approximately 75% to 85% of our sales are made through distributors. In our International segment, approximately 55% to 65% of our sales are made through distributors. The underlying principles of revenue recognition are identical for both categories of customers and revenue is generally recognized at a point in time as described below. We account for revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers , which we adopted on January 1, 2018, using the modified retrospective method. Revenue from the sale of products is recognized when there is persuasive evidence of an arrangement and control passes to the customer, which generally occurs either when product is shipped to the customer or, in the case of most U.S. distributor customers, when product is delivered to the distributor's delivery site. We establish our shipping terms according to local practice and market characteristics. We do not ship product unless we have an order or other documentation authorizing shipment to our customers. Our payment terms vary by the type and location of our customer and the products offered. The term between invoicing and when payment is due is not significant. Refer to Note 9Segment Information for disaggregation of revenue by segment and product group, as we believe this best depicts how the nature, amount, timing and uncertainty of our revenue and cash flows are affected by economic factors. Revenue is measured as the amount of consideration we expect to receive in exchange for transferring goods or providing services. Amounts billed and due from our customers are classified as receivables on the consolidated balance sheet. We make appropriate provisions for uncollectible accounts receivable which have historically been insignificant in relation to our net sales. Certain contracts with customers, primarily distributor customers, have an element of variable consideration that is estimated when revenue is recognized under the contract to the extent that it is material to the individual contract. Variable consideration includes volume incentive rebates, performance guarantees, price concessions and returns. Rebates are based on achieving a certain level of purchases and other performance criteria that are documented in established distributor programs. These rebates are estimated based on projected sales to the customer and accrued as a reduction of net sales as they are earned by the customer. The rebate accrual is reviewed monthly and adjustments are made as the estimate of projected sales changes. Product returns, including an adjustment for restocking fees if it is material, are estimated based on historical return experience and revenue is adjusted. Sales, value add and other taxes collected with revenue-producing activities and remitted to governmental authorities are excluded from revenue. Depending on the terms of the arrangement, we may defer revenue for which we have a future obligation, including training and extended warranty and technical services, until such time that the obligation has been satisfied. We use an observable price, or a cost plus margin approach when one is not available, to determine the stand-alone selling price for separate performance obligations. We have elected to recognize the cost for freight and shipping as an expense when control of the product has passed to the customer. These costs are included within the Cost of Products Sold line on the Condensed Consolidated Statement of Income. We typically receive interim milestone payments under certain contracts, including our fixed gas and flame detection projects, as work progresses. For some of these contracts, we may be entitled to receive an advance payment. Revenue for these contracts is generally recognized as control passes to the customer, which is a point in time upon shipment of the product, and if applicable, acceptance by the customer. We recognize a liability for these advance payments in excess of revenue recognized and present it as contract liabilities on the condensed consolidated balance sheet. The advance payment is typically not considered a significant financing component because it is used to meet working capital demands that can be higher in the early stages of a contract and to protect us from the other party failing to adequately complete some or all of its obligations under the contract. In some cases, the customer retains a small portion of the contract price, typically 10% , until completion of the contract, which we present as contract assets on the condensed consolidated balance sheet. Accordingly, during the period of contract performance, billings and costs are accumulated on the condensed consolidated balance sheet as contract assets or contract liabilities, but no income is recognized until completion of the project and control has passed to the customer. As of September 30, 2018 , there were no material contract assets or contract liabilities recorded on the Condensed Consolidated Balance Sheet. Practical Expedients and Exemptions We do not disclose the value of unsatisfied performance obligations for (i) contracts with an original expected length of one year or less and (ii) contracts for which we recognize revenue at the amount to which we have the right to invoice for services performed. We do not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. We generally expense sales commissions when incurred because the amortization period would have been one year or less. These costs are recorded within selling, general and administrative expenses in our Condensed Consolidated Statement of Income.